mid and late holocene fluvial dynamics in the tropical guapi macacu catchment southeast brazil the role of climate change and human impact abstract deeply incised middle to late holocene fluvial sediments of several streams in the tropical guapi macacu river catchment in the state of rio de janeiro were investigated with stratigraphical sedimentological and geochronological methods these investigations revealed multiple changes of the fluvial dynamics during the holocene triggered by a millennial climate change and the post colonial increase of land use reduced fluvial dynamics and geomorphic stability prevailed in this region during the relatively dry mid holocene from 6 6 until 4 7 cal ka bp this phase of stability was followed by a period of geomorphic activity as indicated by increased fluvial dynamics from this date this overall environmental change corresponds well with the onset of quasi modern humid climate conditions in southeastern brazil during the mid to late holocene transition a new period of activity has taken place since 0 29 cal ka bp in relation with the start of european colonization and increased land use pressure large areas of atlantic forests were converted into agricultural and pasture land causing strong soil erosion and destabilized slopes the results of these investigations improve the existing holocene landscape evolution model and highlight that under the given specific climatic and environmental conditions even a closed forest cover does not necessarily result in geomorphic stability

the collapse of megafaunal populations in southeastern brazil whether humans or climate change caused the extinction of megafaunal populations is actively debated caves in the lagoa santa provide mixed assemblages of megafauna and human remains however it remains uncertain the extent to which humans and megafauna interacted or overlapped temporally here we present the first paleoecological record from lowland south america that tracks the decline of megafauna and its ecological implications we provide a data set for pollen charcoal and sporormiella from two lakes in southeastern brazil that span the last 23 000 yr the data showed reduced abundances of sporormiella and an inferred megafaunal population decline that began 18 000 yr ago with the functional extinction occurring between 12 000 and 11 500 yr ago population declines coincided with wet events the age of the final megafaunal decline is within the range of the first human occupation of the region our data are consistent with climate causing the population collapse with humans preventing population recovery and inducing extinction we did not observe some of the ecological repercussions documented at other sites and attributed to the megafaunal extinction habitat specific ecological consequences of the extinction add to the heterogeneity of late pleistocene and early holocene landscapes

holocene fire and vegetation changes in southeastern brazil as deduced from fossil charcoal and soil carbon isotopes abstract carbon isotopes of soil organic matter som and radiocarbon dating on charcoal from nine soil profiles collected under native forest vegetation in londrina state of parana anhembi botucatu and jaguariuna sao paulo and salitre minas gerais southeastern brazil were used to evaluate the vegetation changes and to establish the chronology 13 c and 14 c data in som and charcoal respectively indicate that c 4 plants were the dominant vegetation in londrina and jaguariuna during the late pleistocene until middle holocene probably associated with the presence of a drier climate in anhembi and botucatu c 3 plants dominate the landscape during the period a probable mixture of c 3 and c 4 plants occurred in salitre during the holocene this study is part of a main research program related to palaeoenvironmental reconstruction of vegetation and climate in distinct regions of brazil during the last 20 000 years

evaluation of last glacial maximum sea surface temperature reconstructions through their influence on south american climate 1 the consistency of land based and ocean based last glacial maximum lgm proxy evidence on and near south america is evaluated by utilizing a regional climate model rcm the relatively high resolution of the rcm brings model output closer to the spatial scales of the geological reconstructions this is important because proxy sites only a few tens of kilometers apart can yield markedly different interpretations of lgm climate along with differences in orbital parameters co2 concentrations and vegetation four versions of lgm sea surface temperatures ssts climate long range investigation mapping and prediction climap schafer neth and paul s 2003 core version paul and schafer neth s 2003 line version and coupled gcm output from shin et al 2003 are used to generate four realizations of the lgm climate in the model mean annual surface temperature mean temperature of the coldest month and aridity differences from a present day simulation are compared with the geological reconstructions over south america to evaluate the consistency of the land and ocean based reconstructions model results suggest that the tropical atlantic during the lgm was not significantly cooler than climap s original estimates simulations utilizing tropical atlantic lgm ssts cooler than climap estimates yield unrealistically warm lgm surface conditions over the equatorial amazon basin reductions in evaporation and the atmosphere s moisture content over too cold tropical oceans lead to a reduction in cloud cover over the amazon and increases in solar heating of the surface all of the lgm sst simulations produce drier conditions over tropical south america however the extent of the aridity is associated with the degree of cooling in the surrounding oceans especially the tropical atlantic the line version lgm ssts of paul and schafer neth 2003 are recommended

strain fabric analysis applied to hydrothermal ore deposits emplaced during changing geodynamical conditions infiernillo and las picazas san rafael massif argentina abstract infiernillo and las picazas are two small hydrothermal ore deposits in the northern san rafael massif argentina they are genetically linked to the permian choiyoi volcanic province which reflects the transition from a convergent plate margin to an extensional regime calc alkaline early permian lower choiyoi magmatism was syntectonic with transpressional deformation of the san rafael orogeny whereas transitional late permian upper choiyoi sequences were emplaced under a transtensional regime during the post san rafael extension infiernillo is a cu mo porphyry type deposit hosted by pyroclastic rocks of the lower choiyoi it consists of a central quartz plug surrounded by a potassic and a phyllic halo and a set of peripheral polymetallic cu pb zn veins cropping out close to the alteration zone the las picazas deposit consists of a group of low sulfidation epithermal galena bearing veins hosted by early palaeozoic meta sediments strain fabric and available 2 d and 3 d kinematic analyses were performed in order to define the relationships between both deposits and the geodynamic scenario these data reveal that a porphyry emplacement at infiernillo occurred during the declination of the san rafael orogeny shortly before the change in stress regime and b las picazas low sulfidation epithermal veins were emplaced during the subsequent transtensional post san rafael regime these results prove that each ore deposit is linked to a different stress regime reflecting the change in geodynamical conditions that prevailed during the emplacement of the choiyoi volcanism thus strain fabric analysis at both ore deposits allows us to confirm that the tectonic regime is a major factor in controlling the mineralization style of hydrothermal ore deposits

shear zones as a new type of palaeostress indicator this paper proposes that shear zones act as palaeostress indicators in much the same way as brittle faults several hundred shear zones from both the limbs of the variscan langland mumblcs anticline south wales are treated using the graphical and numerical methods of fault slip analysis estimated palaeostress directions derived from shear zones are characterized by greater scatter than where brittle faults are used as stress indicators an important reason for this is the fact that on some shear zones the direction of maximum shear stress slip lineation is not perpendicular to the line of s c intersection as a consequence the use of slip lineations produces better solutions than cases where the slip direction is inferred as a line perpendicular to the s c intersection the filtering of data to reduce the scatter in the results produces insignificant improvement and is considered unnecessary

holocene palaeoenvironmental reconstruction in norteastern brazi inferred from polen charcoal and carboon isotope records soils in the barreirinhas region maranhao state were sampled for 613 c analysis and buried charcoal fragments in the soils were radiocarbon dated three soil profiles collected in forested areas around the lagoa do caqo and one in a woody savanna mixture of non arboreal and arboreal species located approximately 10 km southeast of the lagoa were studied a high resolution pollen record was obtained from lake sediments showing that forest vegetation was predominant in the area in the early holocene from approximately 10 000 14c yr bp the pollen spectrum gradually changed suggesting the dominance of open savanna communities these were transformed to a more forested landscape woody savanna from approximately 7500 yr bp the lake sediments also record evidence of fire indicated by buried charcoal particles at several soil depths during the holocene the 613 c analysis of soil organic matter som indicates that from between approximately io0000 yr bp and 9000 yr bp to 4000 yr bp a woody savanna

holocene precipitation and atmospheric changes inferred from river paleowetlands in the bolivian andes abstract in the southern tropical andes previous studies performed on lacustrine basins display large water level fluctuations due to changes in the precipitation minus evaporation balance during the holocene significant changes in groundwater levels were also inferred from river paleowetland deposits in northern chile and the northern bolivian altiplano but the discrepancies which appeared in the data from paleolakes and paleowetlands are still not understood in this paper we present stratigraphy and diatom analyses in new paleowetland records from non glacial valleys these data compared with previous results show that non stormy precipitation recorded by fine and or organic sedimentation dominated continuously from 11 200 to 1500 cal yr bp and that convective rainfall recorded by strong erosion occurred only episodically in the northern altiplano convective rainfall was similar to the type of precipitation which nowadays occurs during the rainy season austral summer when the tropical easterlies from the atlantic reach the bolivian andes non stormy precipitation is interpreted as a result of an intensification of cold air incursions from southern polar regions in good agreement with data from brazil the maximum intensity in cold air incursions occurred during the early holocene and coincided with a climatic optimum in antarctica and a considerably reduced el nino southern oscillation enso during the middle and late holocene cold air incursions decreased and the enso frequency increased we suggest that the interactions between the southern high and low latitudes by means of cold air incursions and associated changes in the west wind flow have been the main mechanisms involved in climatic changes at the latitudes of bolivia

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

separation of multiple stress events by fault striation analysis an example from variscan and younger structures at ogmore south wales the study of minor structures in carboniferous and triassic sedimentary rocks at ogmore by sea bridgend reveals that the observed microstructures are the consequence of successive brittle deformation events age relationships can be deduced from sets of structures consisting of conjugate faults oblique slip faults tension gashes and stylolites from which deductions can be made about the orientations of principal stresses corresponding to pre and post triassic events the demonstrable polyphase tectonic history at ogmore and the occurrence of large numbers of striated faults at four sites allow the opportunity of testing a newly proposed strategy for palaeostress analysis from striated faults with complex stress histories the new technique based on the statistical procedure of cluster analysis involves the sorting of fault slip data into coherent dynamic setsasa preliminary stage of formal stress inversion the fault sets separated using this technique yield stresses which are similar to those deduced from field observations four stress configurations are distinguished of which two are pre triassic in age correlations with previously derived stresses are discussed

environmental and sea level variations on the southeastern brazilian coast during the late holocene with comments on prehistoric human occupation abstract analysis of organic sediments including their diatom and pollen contents was carried out in a swamp forest on the coastal plain of sao paulo state southeastern brazil a palaeoenvironmental reconstruction was made regarding this region where communities of fisher gatherers lived in prehistory producing numerous shell mounds from at least 4900 until 3470 cal yr bp the site was a lagoon surrounded by a relatively open forest the occurrence of shell mounds 50 km from the coast and the peak of human occupation between 5700 and 3300 cal yr bp can be linked to the presence of this great lagoon which formed an important food source the lagoon desiccated ca 3470 cal yr bp i e during the late holocene sea level fall and was replaced by a swamp forest that still exists today this forest was altered during a short period between 1300 and 675 cal yr bp when a freshwater lake or marsh was formed as a result of a rise in groundwater level the climate in the area throughout the middle late holocene ca 5000 cal yr bp to the present has not changed significantly except for three slightly more humid episodes at 3470 2750 ca 1940 and 1300 675 cal yr bp no indications of human impact on the vegetation during this period could be identified our results show that from 4900 to 3470 cal yr bp sea level was higher than at present contradicting a widely accepted relative sea level trend that suggests that at least two negative sea level oscillations occurred during the holocene i e at 4560 4150 and 3200 2800 cal yr bp our data confirm recent studies instead proposing a continuously declining relative sea level during the late holocene

kinematic and dynamic fault slip analyses implications from the surface rupture of the 1999 chi chi taiwan earthquake the 1999 chi chi earthquake created a 100 km long surface rupture on the chelungpu thrust fault in taiwan due to convergence between the phillipine sea and eurasian plates fault slip measurements were made by several researchers from the entire length of the rupture directly following the earthquake and can thus be attributed to a single tectonic event conventional fault slip analyses are applied to these data and the results are compared with independent seismological and kinematic observations unlike many fault slip analyses complications due to multiple deformations can be categorically excluded and the results can be evaluated from the seismological and plate movement data kinematic analyses of fault slip data that are weighted by displacement show sub horizontal nw se shortening that is parallel to the plate convergence vector a single fault plane solution satisfies almost all the data right dihedra and trihedra solutions also satisfy almost all the surface rupture measurements and give 1 in a nw se orientation that is similar to the results of stress inversion and to inversion from earthquakes in the chi chi earthquake sequence despite criticisms of fault slip analysis methods these results show that fault slip analyses from data collected along major faults which have not witnessed multiple deformation events can be valid homogeneous strain and stress states exist in the sense that kinematic and dynamic solutions can be found that fit essentially all the data and these solutions have tectonic significance

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

late quaternary vegetation and climate dynamics in the serra da bocaina southeastern brazil abstract late quaternary vegetation fire and climate dynamics were studied by pollen and charcoal analysis in the serra da bocaina in the coastal ranges of southeastern brazil rio de janeiro and sao paulo states samples were taken from two cores serra da bocaina 1 and 2 seven radiocarbon dates indicate deposits of late pleistocene to holocene age during the period between 18 570 and 14 570 cal bp wide spread grassland campos with frequent fires existed in the higher serra da bocaina taken together with other evidence this indicates relatively dry and cold climatic conditions for this period upper montane forest occurred in protected valleys or on slopes at lower elevations the conifer araucaria angustifolia has been present in the serra da bocaina since the late pleistocene but populations have fluctuated an erosion hiatus in the late glacial period evidenced by reworked deposits lacking pollen was probably caused by increased rainfall during the younger dryas period upper montane forest taxa expanded during the holocene especially after 7260 cal bp indications are that the early and mid holocene were dry and relatively warm with an annual dry season longer than present day modern patches of campos in the serra da bocaina are remnants of more expansive grasslands during glacial times

climatic events during the late pleistocene and holocene in the upper parana river correlation with ne argentina and south central brazil most quaternary studies in brazil are restricted to the atlantic coast and are mainly based on coastal morphology and sea level changes whereas research on inland areas is largely unexplored the study area lies along the parana river state of parana brazil at 22 43 s latitude and 53 10 w longitude where the river is as yet undammed paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes sedimentological and pollen analyses plus tl and 14c dating were used to establish the following evolutionary history of late pleistocene and holocene climates first drier episode 40 000 8000 bp first wetter episode 8000 3500 bp second drier episode 3500 1500 bp second present wet episode 1500 bp present full size table table options view in workspace download as csv climatic intervals are in agreement with prior studies made in southern brazil and in northeastern argentina

the svecofennian orogen a tectonic model abstract recent geological studies have provided new concepts concerning the timing of the final break up of the archaean craton age data on detrital zircons from sedimentary rocks in sweden and finland show marked similarities and indicate pervasive homogenization of accumulated material geochemical and isotopic studies in sweden and finland suggest the existence of two volcanic belts separated by an area dominated by sedimentary rocks however the ages of metamorphism and plutonism differ in particular the late post 1 85 ga granitoid magmatism was more voluminous in sweden than in finland the svecofennian crust in finland is anomalously thick up to 65 km and is characterized by a high velocity lower crust of variable thickness the evolution of the svecofennian orogen is modelled by opening of the pre svecofennian ocean at 1 95 ga and progressive accretion of two arc complexes to the archaean craton between 1 91 1 87 ga initial accretion at 1 91 ga led to thrusting of the slices of an island arc complex and proterozoic marine strata onto the thickening craton margin subduction reversal with simultaneous anti clockwise rotation of the converging plate or convergence of another plate resulted in subduction below the newly accreted arc complex the tectonic style at the craton margin changed from thrusting to lateral displacement in the east in finland in the west in sweden the subduction zone retreated along a transform fault a large sedimentary basin closed in the east 1 89 ga ago when another arc complex collided against the accreted one collision resulted in lithospheric thickening subsequent delamination of the thickened lithosphere and compensation by a hot mantle underplate and large scale granitoid magmatism as a result of mixing between mantle magma and remelted arc complex material the thick dense layer that formed in the lower crust as the result of underplating kept the thickened crust in isostatic balance thus the exhumation rate in this area was similar to the rate in areas of thinner crust subduction and sediment accumulation continued in the west until at least 1 87 ga when large areas in the east were already stabilized an intracratonic transpressional zone developed as the result of continued convergence subsequent extensional collapse along the transpressional zone caused melting of svecofennian sedimentary rocks migmatization and generation of the 1 84 1 82 ga anatectic granites of southern finland and central sweden the voluminous post 1 85 ga granitoid magmatism in sweden is tentatively associated with an east west extension that is not related to the extensional collapse

structural analysis of faults related to a heterogeneous stress history reconstruction of a dismembered gold deposit stawell western lachlan fold belt australia in the internationally significant victorian goldfields a complex system of faults dismembers the 5 million ounce magdala gold deposit these faults represent a combination of neoformed faults and inherited faults that reflect deformation associated with stress tensors of variable orientation and stress shape ratio the fault geometry is strongly controlled by the pre existing rheology faults have propagated around the flanks of an antiformal basalt dome along earlier ductile cleavages and the margins of porphyry dykes many of the faults do not have andersonian geometries and there is no correlation between the orientation of the faults and the palaeostress directions much of the faulting is associated with the emplacement of porphyry dykes additional gold mineralisation related to plutonism and late stage deformation post dating the intrusion of the stawell pluton systematic mapping of extension veins associated with faults striations and conjugate joint sets allowed the construction of a revised and more robust history of brittle deformation this successfully predicted the offset direction of the currently mined magdala ore body beneath the studied system of faults the use of extension veins was a critical aspect of the analysis if striations on the fault surfaces had solely been used the offset direction of the new golden gift orebody would not have been correctly ascertained the palaeostress history was delineated via use of compression and tension dihedra stress inversion of slip data and calculation of theoretical resolved shear stress for faults with orientations similar to those mapped the calculation of theoretical resolved shear stress directions highlights the importance that the intermediate stress has on the slip direction for faults whose pole does not lie in the plane containing 1 and 3

modification of a palaeoproterozoic porphyry like system integration of structural geochemical petrographic and fluid inclusion data from the aitik cu au ag deposit northern sweden the aitik cu au ag deposit in the gallivare area in northern sweden is sweden s largest sulphide mine with an annual production of 35 mt of ore and the biggest open pit operation in northern europ

southern oscillation signal in south american palaeoclimatic data of the last 7000 years abstract during strong el nino events rainfall anomalies and changes in wind patterns are observed in different regions of south america along the central brazilian coast during the 1983 el nino year the frontal systems were blocked to the south provoking a reversal of the longshore sand transport long duration reversals of longshore transport were also recorded in holocene beach ridge terraces from the rio doce coastal plain this led to the formulation of a model relating these reversals of longshore transport to el nino like conditions el nino like conditions are past average climate situations that generate the same perturbations as the strong el nino events observed during the last decade they are likely to correspond to the long duration low phase of the southern oscillation to confirm this hypothesis we compared the holocene beach ridge record with other palaeoenvironmental records from regions where strong el nino events would have a substancial signal as well 1 water level fluctuations of lake titicaca 2 a pollen and sediment record in an eastern amazonian lake 3 changes of the rio xingu discharge in eastern amazonia and 4 variations of sand supply at the rio piura and rio chira outlets in the sechura desert the occurrences of el nino like conditions were numerous before 3900 3600 yr b p absent between 39003600 and 2800 2500 yr b p and infrequent after 2800 2500 yr b p

a stress inversion procedure for polyphase fault slip data sets palaeostress estimation from striated fault data is frequently frustrated by the fact that natural fault data are heterogeneous in the sense that they cannot satisfactorily be explained by reactivation brought about by a single stress tensor in many instances there is clear evidence to show that striation data can record the effects of multiple stress events any attempt to find the tensor which best fits or explains such dynamically mixed data sets risks determining a spurious stress state which is some form of compromise between the real stress states corresponding to different tectonic phases to avoid this problem a strategy is proposed here which involves an initial separation of the raw data into coherent sub sets prior to formal stress inversion this separation is performed by assigning attributes to each fault which describe the fault s compatibility with trial stress tensors using these attributes faults can be grouped into dynamically homogeneous families using the statistical techniques of cluster analysis

evidence of dry and cold climatic conditions at glacial times in tropical southeastern brazil last glacial paleoenvironments have been reconstructed from a pollen and charcoal record analyzed in organic sediments and dated between ca 18 000 and 48 00014c yr b p the site is located near the village catas altas in the lower highland region of southeastern brazil the last glacial landscape was covered by extensive areas of subtropical grasslands and small areas of gallery forests along the rivers where tropical semideciduous forests and cerrado ecosystems exist today the subtropical gallery forests were composed ofaraucariaforest trees such asaraucaria angustifolia podocarpus drimys ilex andsymplocos paleofires were frequent the record indicates that subtropical grassland vegetation which today is found in patches on the highlands in southern brazil especially in the state of santa catarina expanded from southern brazil to southeastern brazil over a distance of more than 750 km from latitudes of about 28 s to at least 20 s the completely different last glacial environment in comparison to the present day environment reflects a dry and cold climate with strong frosts during the winter months temperatures of 5 7 c below those of the present are inferred for the last glaciation

absence of last glacial maximum records in lowland tropical forests abstract environmental conditions of the lowland tropical forests during the last glacial maximum lgm between ca 20 000 and 18 00014c yr b p are reevaluated in terms of dating control and lithology analyzed in seven pollen records from south america the reevaluation shows that probably in none of the published records are lgm sediments present or abundant this conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates these findings suggest that the lgm was represented probably by a hiatus of several thousand years indicative of drier climates than before or after

stable isotope evidence for the origin of the mesoproterozoic starra au cu deposit cloncurry district northwest queensland new stable isotope data are consistent with a metasomatic origin for the controversial mesoproterozoic ironstone hosted au cu deposit at starra in the cloncurry district of northwest queensland this supports textural and mineralogical evidence that the ore bearing ironstones formed after the peak of metamorphism and were strongly controlled by brittle ductile deformation three dominant paragenetic stages are recognized these are 1 early widespread na ca metasomatism quartz albite scapolite actinolite 2 localized k fe metasomatism biotite magnetite hematite quartz pyrite and 3 mineralization quartz anhydrite barite hematite calcite gold pyrite chalcopyrite bornite chalcocite chlorite muscovite crosscutting anhydrite veins associated with carbonate or hematite are rare in the upper parts of the system but more common at depths greater than 700 m stage 3 minerals demonstrate that the ore fluid was highly oxidized a restricted range of fe oxide delta 18 o implies isotopically similar fluids were responsible for the magnetite ironstones and later hematite alteration associated with gold and sulfides between 0 2 to 3 3ppm except for one magnetite at 5 4ppm sulfur isotope compositions suggest that pyrite 0 2 to 3 9ppm chalcopyrite 5 8 to 0 7 and 14 6ppm bornite 4 7ppm chalcocite 0 1ppm and anhydrite 1 1 2 4ppm all formed from the same sulfur source anhydrite delta 34 s falls within the sulfide range suggesting that the sulfate inherited its delta 34 s through hydrolytic processes similar to those of some porphyry environments delta 13 c of ore stage carbonates range from 7 3 to 2 2 per mil temperatures based on stage 2 quartz magnetite pairs imply 400 degrees to 500 degrees c for ironstone formation and stage 3 calcite hematite pairs indicate 180 degrees to 330 degrees c for mineralization stage 2 fluid inclusions have homogenization temperatures between 345 degrees and 615 degrees c and salinities of 34 to 52 wt percent nacl equiv stage 3 fluid inclusions homogenized between 225 degrees and 360 degrees c and have salinities of 30 to 42 wt percent nacl equiv calculated delta 18 o fluid compositions for magnetite quartz and hematite calcite average 7 8 per mil and 9 5 per mil respectively fluid compositions for stages 2 and 3 fall within the range for a magmatic or metamorphic fluid however combined stable isotope and fluid inclusion data and thermodynamic considerations suggest a magmatic metasomatic origin for both the magnetite ironstones and the highly oxidized mineral assemblage associated with high grade gold deposition

hybrid genesis of jurassic fayalite bearing felsic subvolcanic rocks in south china inspired by petrography geochronology and sr nd o hf isotopes abstract fayalite bearing felsic fbf magmatic rocks are a special type of granitic rocks with controversial origins a suite of fayalite and ferrosilite bearing subvolcanic rocks namely the xishan fbf rocks in south china is investigated in this study the xishan fbf rocks have high sio 2 contents of 69 70 wt high k 2 o na 2 o ratios of 1 71 1 95 and high feo t feo t mgo ratios of 0 88 0 89 fayalite fo 7 3 9 6 and ferrosilite fs 74 1 76 5 minerals are found in the xishan fbf rocks according to the unmix function of isoplot the zircon u pb ages and initial hf isotope compositions are categorized into two groups with ages of 156 6 ma and 151 5 ma and e hf t values of 7 1 and 5 2 respectively the minerals show 18 o values of 8 8 9 8 for zircon 6 0 8 1 for fayalite and 7 0 8 2 for ferrosilite the oxygen isotope fractionations between ferrosilite and fayalite opx ol vary from 0 8 to 1 5 which indicates disequilibrium crystallization whole rock analyses show high initial 87 sr 86 sr ratios of 0 7169 to 0 7180 and negative e nd t values of 7 3 to 6 8 zircon analyses show e hf t values of 9 1 to 3 8 and 18 o values of 8 8 9 8 so whole rock and zircon isotopes indicate a crustal signature based on these mineralogical and geochemical data the xishan fbf rocks were attributed to a type granites and derived from the mixing of two batches of crustal magmas which were all derived from the partial melting of ancient igneous protolith under the conditions of high temperature 683 893 c moderate water 3 5 wt and low oxygen fugacity lg f o 2 1 21 such rigorous physical conditions may be common for the fbf igneous rocks all over the world which may be the primary factors controlling occurrence of the fbf rocks in limited volume and quantity

late quaternary paleoclimate in semiarid northeastern brazil from u series dating of travertine and water table speleothems abstract fossil travertine and subaqueous speleothems in presently dry caves suggest periods of enhanced ground water recharge during the quaternary period in semiarid northeastern brazil travertine deposits and water table speleothems were dated by the 230 th 234 u technique yielding new evidence for the timing of past periods of increased rainfall the travertine was deposited in two distinct phases extensive in situ deposits during marine isotope stage 2 and fragmentary indurated deposits dating to ca 400 000 yr b p possibly marine isotope stage 10 or 12 dating of water table speleothems showed that the regional water table was 13 1 m above the present level at the last glacial maximum a second site yielded ages suggesting a still higher water table during marine isotope stage 6 these new data demonstrate that northeastern brazil did not follow the general pattern of a dry last glacial maximum as suggested by other continental records in amazonia and southeastern brazil and as depicted in recent general circulation model gcm simulations our results thus indicate that significant variability in regional rainfall patterns occurred in the area during glaciations and caution against overgeneralization of paleoclimate patterns

late quaternary vegetational and climate dynamics in southeastern brazil inferences from marine cores geob 3229 2 and geob 3202 1 abstract late quaternary palaeoenvironments from southeastern se brazil have been reconstructed by pollen analysis of two marine sediment cores the core geob 3229 2 19 38 5 s 38 43 0 w 780 mbsl from the central depression south of the abrolhos bank is 505 cm long and 80 kyr bp old the core geob 3202 1 21 37 0 s 39 58 7 w 1090 mbsl from the upper continental slope off rio paraiba do sul is 495 cm long and 52 kyr bp old chronological control for core geob 3202 1 is based on seven ams radiocarbon dates from individuals of the foraminiferal species globigerinoides sacculifer the age scale for core geob 3229 2 was obtained by the detailed correlation of the oxygen isotope and x ray fluorescence records of both cores the two marine pollen records document vegetational changes in the drainage areas of two major se brazilian rivers the rio doce and the rio paraiba do sul which probably transported most of the pollen and spores deposited in the marine sediments during glacial times grassland vegetation dominated the landscape and atlantic rainforest and semideciduous forest were markedly reduced small areas of subtropical araucaria forest occurred in southeastern se brazil while cerrado vegetation was rare maximal grassland expansion and atlantic rainforest reduction were found during the last glacial maximum reflecting cold and relatively dry climatic conditions during the late glacial period grassland decreased and lowland forest taxa increased indicating wetter and warmer conditions comparison between the two marine pollen records with terrestrial records from the two river drainage areas confirms that grassland dominated the glacial age landscape reconstructed from terrestrial records

south and southeast brazilian grasslands during late quaternary times a synthesis fourteen pollen records from the south s and the southeast se brazilian regions have been synthesised late glacial records from s brazilian highlands document the predominance of grassland campos where today araucaria forests occur records from se brazil show that during pre and full glacial times modern tropical semideciduous forest and cerrado savanna to dry forest were mostly replaced by grassland and some subtropical gallery forest modern montane araucaria forests and cloud forests in se brazil were mostly replaced by grassland during pre and full glacial times there is evidence that the modern tropical atlantic rainforest in s brazil was significantly reduced and replaced by cold adapted forest taxa or grassland during glacial especially during full glacial times the synthesis indicates that grasslands dominated the s and se brazilian landscape during the late pleistocene where today different forest ecosystems exist grassland extended over 750 km from s to se brazil from latitudes of about 28 27 s to at least 20 s these results indicate that climates in the region were markedly drier and 5 7 c cooler during glacial times antarctic cold fronts must have been much stronger and more frequent than today studies from s brazil show that huge areas of late pleistocene campos vegetation were still found on the s brazilian highlands during early and mid holocene times reflecting dry climatic conditions with an annual dry period of probably 3 months modern wet climatic conditions with no or only short dry periods were not established until the late holocene period when araucaria forests replaced large areas of grassland vegetation after about 3000 14c yr b p and especially after 1500 1000 14c yr b p

late quaternary vegetational and climate dynamics in northeastern brazil inferences from marine core geob 3104 1 abstract late quaternary paleoenvironments from northeastern ne brazil have been studied by pollen analysis of marine sediment the studied core geob 3104 1 3 40 s 37 43 w 767 m b s l from the upper continental slope off ne brazil is 517 cm long and 42 000 14 c yr bp old chronological control was obtained by 12 radiocarbon ams dates from individuals of the foraminiferal species globigerinoides sacculifer modern pollen analogs were received from 15 river lake and forest soil surface samples from ne brazil marine pollen dates indicate the predominance of semi arid caatinga vegetation in ne brazil during the recorded period between 42 000 and 8500 14 c yr bp the increased fluvial input of terrigenous material with high concentrations of pollen and specially fern spores into the marine deposits about 40 000 33 000 and 24 000 14 c yr bp and between 15 500 and 11 800 14 c yr bp indicate short term periods of strong rainfall on the ne brazilian continent the expansion of mountain floodplain and gallery forests characterize the interval between 15 500 and 11 800 14 c yr bp as the wettest recorded period in ne brazil which allowed floristic exchanges between atlantic rain forest and amazonian rain forest and vice versa the paleodata from core geob 3104 1 confirm the in general dry pre last glacial maximum lgm and lgm conditions and the change to wet lateglacial environments in tropical south america the annual movement of the intertropical convergence zone over ne brazil the strong influence of the antarctic cold fronts and changes of the high pressure cell over the southern atlantic may explain the very wet lateglacial period in ne brazil the documented ne brazilian short term signals correlate with the documented dansgaard oeschger cycles and heinrich events from the northern hemisphere and suggest strong teleconnections

late holocene intensification of colds fronts in southern brazil as indicated by dune development and provenance changes in the sao francisco do sul coastal barrier abstract holocene coastal barriers from southern brazil present great geomorphological changes during their late stages of development in this study we investigate the holocene evolution of the sao francisco do sul sfs barrier through geomorphological heavy minerals and grain size analyses constrained by optically stimulated luminescence osl dating the sfs barrier stands out among the southern brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion the progradation of the sfs barrier started at least 4914 478 years ago and had a pronounced morphodynamic shift around 1891 155 years ago this shift is characterized by episodic development of parabolic dunes migrating to nnw associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the sfs barrier this morphodynamic provenance shift resulted from the strengthening of sse winds and associated wave systems responsible for the northward alongshore drift implying intensification of cold fronts coupled with higher precipitation since 1891 155 years ago osl dating combined with grain size heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the late holocene reconstruction of the late holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes

post lgm sedimentation on the outer shelf upper slope of the northernmost part of the sao paulo bight southeastern brazil abstract sedimentary and isotope data as well as 14 c ams dating on 15 box cores were used to identify the main post last glacial maximum lgm processes in the outer shelf and upper slope of the northernmost part of the sao paulo bight southeastern brazil results show slight but significant variations in calcium carbonate total sulphur and nitrogen contents as well as carbon and oxygen isotope ratios sedimentation rates varying from 5 to 184 mm kyr 1 are controlled by the shelf and upper slope morphology the brazil current meander dynamics and the coastal water offshore motion

mid to late holocene evolution of transgressive dunefields from rio grande do sul coast southern brazil abstract the aim of this paper is to examine the dunefield evolution of the rio grande do sul rs coastal stretch from torres to mostardas which presents progradational aggradational and retrogradational barriers the stratigraphy and sedimentary facies of 26 cores along 9 profiles were analyzed the stratigraphy of the cores along the profiles agreed with the suggested barrier types the northern area comprises prograded barriers in jardim do eden and magisterio retrograded barriers in dunas altas an aggradational barrier and the southernmost profiles solidao sao simao and mostardas retrograded barriers three major periods of soil formation and dunefield stabilization were found from 4820 to 3970 cal yr bp in 2760 2460 cal yr bp and from 1570 to 710 cal yr bp these periods coincide with periods where the literature cites an increase in moisture during the mid to late holocene this coincidence of soil formation and wet climate indicates that the climate might be controlling dunefield evolution on the rs coast since 5000 yr bp the stratigraphic data of the three most representative cores were correlated and along with the available ages from palaeosols and the facies descriptions 10 phases of aeolian activity and stabilization were recognized for the mid littoral of rs

stress space striated faults deformation twins and their constraints on paleostress abstract stress space is used to illustrate a discussion of the range of stress tensors theoretically compatible with striated faults and with deformation twinning other than friction laws each of the main constraints placed on stress by such data specifies the magnitude of a component of traction being linear in elements of the stress tensor such a constraint by each datum is represented in stress space by a hyperplane comparison at each level of constraint orientation sense of shear assumption of critical ratio or value of shear stress for faulting twinning is made for a single datum followed by consideration of sets of data and stress tensor reduction at no level of constraint are striated faults and deformation twins equivalent fault data cannot constrain absolute values of stress components data for untwinned crystals within twinned untwinned sets provide the fullest limit to values of deviatoric stresses paleostress estimates from twinned untwinned data are generally preferable to those from striated faults

palaeo stress fields in the variscan foreland during the carboniferous from microstructural analysis in the british isles abstract north of the variscan front the carboniferous series of the british isles is affected by mainly n s trending folds which are almost perpendicular to this e w oriented front flat and unconformable overlying permian strata demonstrate a variscan age for the deformation a microtectonic survey made in dinantian and to a lesser extent namurian calcareous layers has revealed two successive events according to chronological criteria the first event maximum stress e w trending led to the formation of n s folds with local reorientation in the vicinity of major pre existing faults this compression may have been active since the namurian it pre dates a second compressional event orientated n s which is related to the final emplacement of the variscan nappes

stratigraphy of near valley head quaternary deposits and evidence of climate driven slope channel processes in southern brazilian highlands abstract during the past 40 years colluvial and alluvial deposits have been used in brazil as good indicators of regional landscape sensitivity to quaternary environmental changes in spite of the low resolution of most of the continental sedimentary record geomorphology and sedimentology may favor palaeoenvironmental interpretation when supported by independent proxy data this paper presents results obtained from pedostratigraphic sequences in near valley head sites of southern brazilian highlands based on geomorphologic sedimentologic micromorphologic isotopic and palynologic data results point to environmental changes with ages that coincide with marine isotopic stages mis 5b 3 2 and 1 during the late pleistocene although under temperatures and precipitation lower than today the local record points to relatively wet local environments where shallow soil water saturated zones contributed to erosion and sedimentation during periods of climatic change as during the transition between mis 2 and mis 1 late pleistocene events with ages that coincide with the northern hemisphere younger dryas are also depicted during the mid holocene slope wash deposits suggest a climate drier than today probably under the influence of seasonally contrasted precipitation regimes the predominance of overland flow related sedimentary deposits suggests an excess of precipitation over evaporation that influenced local palaeohydrology this environmental condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area due to relative sensitiveness resilience and short source to sink sedimentary pathways near valley head sites deserve further attention in quaternary studies in the humid tropics

late quaternary vegetation climate and fire history from the tropical mountain region of morro de itapeva se brazil late quaternary paleoenvironments have been interpreted from a 35 000 yr b p pollen and charcoal record from morro de itapeva 22 47 s 45 32 w 1850 m a s l in the se brazilian highlands changes in taxa composition and elevational shifts in high elevation grassland campos de altitude araucaria forest cloud forest and atlantic rain forest all of which can be found in the study area today indicate climatic changes in the past expanded high elevation grasslands absence of araucaria forest cloud forest and atlantic rain forest during the recorded last glacial period ca 35 000 17 000 yr b p suggest a climate markedly cooler and drier than today development of a sphagnum peat bog rare presence of araucaria forest taxa and existence of a narrow cloud forest and rain forest belt at lower elevations during the late glacial period 17 000 ca 10 000 yr b p indicate a change to a cool and somewhat moister climates during the early holocene cloud forest developed close to the study site reflecting a warm and moist climate on the east facing slopes but a drier climate on the highland plateau evidenced by the rare presence of araucaria and podocarpus only during the late holocene moisture increases in the highlands suggested by the higher frequency of araucaria and podocarpus fires were more frequent during the last glacial than during the holocene

the jabal akhdar dome in the oman mountains evolution of a dynamic fracture system the mesozoic succession of the jabal akhdar dome in the oman mountains hosts complex networks of fractures and veins in carbonates which are a clear example of dynamic fracture opening and sealing in a highly overpressured system the area underwent several tectonic events during the late cretaceous and cenozoic including the obduction of the samail ophiolite and hawasina nappes followed by uplift and compression due to the arabia eurasia convergence this study presents the results of an extensive tectonic survey and correlates subseismic scale structures in jabal akhdar faults fractures veins and stylolites with the main tectonic events in the northeastern arabian plate as some of the studied formations host large oil reserves in neighboring areas determining the relative timing of these events in the exhumed rocks is important to understand hydrocarbon distribution and fracture patterns in these reservoirs the formation of early veins and stylolites in the oman mountains is followed by top to the south layer parallel shearing that may be associated with the obduction of the samail and hawasina nappes this compressional tectonic event is followed by normal dip slip to oblique slip faults and veins top to the northeast layer parallel shearing which corresponds to the first stage of exhumation of the autochthonous rocks offsets these structures our new data indicate that this first phase of events is overprinted by complex strike slip networks of veins and fractures as well as by the reactivation and onset of seismic scale faults strike slip structures belong to three distinct events the first one nw se oriented compression is probably associated with the oblique collision of the indian plate against the arabian platform during the late campanian to the mid eocene the second event e w oriented compression is likely to have been formed during the late oligocene middle miocene during uplift the last event ne sw oriented compression probably took place during the miocene pliocene structures of the first two strike slip events have the same orientation as seismic scale faults observed in the subsurface of oman and abu dhabi in addition increasing vein intensity towards the top of the autochthonous formations in the oman mountains as well as the small angle between conjugate vein sets indicate that high fluid pressures that are thought to be present during strike slip deformation

late quaternary fires and grassland palaeoecology of mount kenya east africa evidence from charred grass cuticles in lake sediments abstract multi proxy evidence from sacred lake on mount kenya including pollen and compound specific carbon isotope data indicates grassland expansion at the last glacial maximum lgm circa 18 000 14c years bp but lacks the taxonomic resolution with which to derive ecological inferences about past grasslands analysis of grass cuticles preserved in east african lake sediments is presented here as a palaeoecological tool for addressing this problem sub fossil grass cuticles retain micro morphological features that often permit identification to subfamily supertribe tribe and in some instances genus or species level a method for isolating and identifying this novel resource is presented along with an analysis of late quaternary to recent age sediments from sacred lake mount kenya data derived from 43 sediment samples and over 5000 graminoid cuticles support isotopic evidence for the presence of grasslands at sacred lake during the lgm size class analysis of charred graminoid fragments indicates that relatively local low intensity fires occurred throughout the sequence current autoecological understanding of the taxa identified indicates that the grassland present at the lgm possessed specific adaptations to burning we conclude that fire was an important landscape feature on mount kenya reinforcing the impact of past variations in climate and atmospheric co2

on the mechanism of resorption zoning in metamorphic garnet an analytical electron microscope study of almandine garnet from a metamorphosed al fe rich rock revealed detailed composition profiles and defect microstructures of resorption zoning along fluid infiltrated veins and even into the garnet ilmenite inclusion interface this indicates a limited volume diffusion for the cations in substitution mainly ca and fe and an interface controlled partition for the extension of a composition invariant margin a corrugated interface between the ca rich margin zone and the almandine garnet core is characterized by dislocation arrays and recovery texture further suggesting a resorption process facilitated by diffusion induced recrystallization diffusion induced dislocation migration and diffusion induced grain boundary migration integrated microstructural and chemical studies are essential for understanding the underlying mechanisms of processes such as garnet zoning and its modification without this understanding it will not be possible to reliably use garnet compositions for thermobarometry and other applications that rely on garnet chemical information

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

geology mineral chemistry and formation conditions of calc silicate minerals of astamal fe lree distal skarn deposit eastern azarbaijan province nw iran the astamal fe lree skarn deposit is the largest iron skarn in nw iran it is a unique case as a distal skarn deposit which crops out approximately 600 m from the associated oligo miocene granodioritic pluton this deposit formed in the south southwest of the pluton where fractures and faults within the upper cretaceous volcano sedimentary host rocks acted as conduits for the mineralizing fluids the deposit contains three iron ore bodies southern northern and eastern the main mineral assemblage within the ore zones is characterized by magnetite pyrrhotite and pyrite with lesser quantities of chalcopyrite hematite goethite and limonite the skarn minerals predominantly comprise garnet epidote actinolite calcite quartz clinopyroxene and chlorite in order of abundance retrograde alteration is strongly developed in the skarn zone where most of the garnet has been pervasively altered to secondary minerals e g epidote calcite and quartz both in the rims and the cores whereas the majority of the clinopyroxene has been replaced by a hydrous retrograde mineral assemblage e g tremolite actinolite and chlorite garnets with andradite grossular compositions are the dominant mineral in the skarn zone which are generally isotropic with a narrow compositional range along the growth lines adr94 3 64 5grs21 9 2 7alm11 1 0 2 these garnets are fe rich and have high fe fe al ratios between 0 96 and 0 78 cu and ni are enriched in the garnets this suggests that these elements were enriched in the hydrothermal fluids from which the garnet precipitated this is supported by the presence of chalcopyrite and ni bearing massive magnetite in the study area which also suggests that cu and ni were enriched in the late stage ore bearing hydrothermal fluids clinopyroxene with a hedenbergitic composition is generally homogenous and has particularly high fe fe mg ratios between 0 99 and 0 86 and is poor in tio2 mno and cr2o3 high zn concentrations were also detected in the clinopyroxenes up to 1044 ppm despite an absence of significant zn mineralization such as sphalerite in the district therefore it is believed that the proportion of zn in the hydrothermal fluids decreased significantly from the time of clinopyroxene formation to the period of the sulfide deposition phase allanite and lree bearing epidotes are the main lree bearing minerals in this deposit the epidote is also fe rich with high fe fe al ratios between 0 32 and 0 44 due to a lack of replacement texture between both garnet and clinopyroxene and garnet and actinolite which is formed by alteration of clinopyroxene it is believed that these two minerals have grown simultaneously and are coexisting minerals in the astamal skarn these minerals can be stable and coexisting at temperatures between 490 and 560 c and log o2 16 to 31

last glacial maximum lgm vegetation changes in the atlantic forest southeastern brazil abstract this study was carried out in a continental atlantic forest located in the southern region of sao paulo state southeastern brazil the aim of the study was to evaluate the vegetation dynamics in 70 km forest ecosystem transect that occurred during the late pleistocene and holocene in this region using the stable carbon isotopes 13 c analysis on soil organic matter som and the 14 c dating of buried charcoal fragments and the humin fraction of som the isotope data 13 c of som in the deeper horizons indicating the presence of more open vegetation than the present with a probable mixture of c 3 and c 4 plants suggesting the presence of a drier climate in the period of 20 ka to 16 14 ka bp from 16 to 14 ka bp to the present a significant predominance of c 3 plants was observed indicating an expansion of the forest probably associated with the presence of a more humid climate than the previous period the results indicated the presence of open vegetation during the late glacial probably associated with a drier period also observed in other regions of brazil the atlantic forest ecosystem seems to have developed at least since the early holocene in southeastern brazil

upper pleistocene to holocene peatland evolution in southern brazilian highlands as depicted by radar stratigraphy sedimentology and palynology paleoenvironmental interpretation of proxy data derived from peatlands is largely based upon an evolutionary model for ombrotrophic bogs in which peat accumulates in still environments reports on proxies obtained from minerotrophic fens where hydrologic inputs are variable are less common in this study a highland peatland in southern brazil is presented through ground penetrating radar gpr and sedimentological palynological and geochronologic data the radar stratigraphic interpretation suggests a relatively complex history of erosion and deposition at the site since the beginning of marine isotope stage 3 mis 3 interstadial period in spite of this radar stratigraphic and palynologic interpretations converge electromagnetic reflections tend to group in clusters that show lateral coherence and correlate with different sediment types while pollen grains abound and are well preserved as a result the study of minerotrophic fens provides a source of proxies suggesting that ombrotrophic bogs are not the only reliable source of data in wetlands for palynological analysis

land sea correlation in southeastern brazil during the last 7 4 cal ka bp vegetational climatic and oceanographic inferences abstract the vegetation history and climate in southeastern brazil as well as the oceanic dynamics of the tropical atlantic ocean offshore were reconstructed for the last 7 4 cal ka bp this reconstruction was based on pollen fern spores and dinoflagellate cysts identified in a marine core cf10 04b it was possible to verify the presence of an ombrophilous forest from 7 4 cal ka bp near the base of the pi zone low concentrations of pollen and fern spores are recorded along with low frequencies of forest taxa and fern spores and an increase in pollen types of open vegetation suggesting less humid climatic conditions than currently observed in the coastal regions of southeastern brazil the assemblages of dinoflagellate cysts suggest a neritic zone with warm upper column temperature high salinity and oligotrophic environment evidenced by the presence of o centrocarpum spiniferites spp and l machaerophorum an increase in tropical waters tw and the approximation of the brazilian current bc in the middle shelf of southeastern brazil in the mid holocene probably influenced the low accumulation of cysts pollen grains fern spores and their associations it is still possible to verify that at approximately 4 6 cal ka bp an increase in the rainfall in the southeastern brazilian region was probably the fundamental factor for the expansion of vegetation mainly based on the considerable increases in hygrophytic and aquatic plants the marked increase in the accumulation of dinoflagellate cysts with the dominance of autotroph taxa mainly o centrocarpum followed by spiniferites spp evidences the warmer waters of the bc and more intense surface upwelling of the south atlantic central water sacw

a new variscan deformation map of england and wales collections of bedding orientations from subareas of 550 km 2 are used to define bedding fabrics from the variscan fold belt and foreland in england and wales the bedding fabrics constructed from data taken from published geological maps 1 50 000 scale are analysed in terms of the scheidegger watson orientation tensor the calculated eigenvalues of the orientation tensor define the average structural trends including the best fit fold axis for each subarea the eigenvectors of the tensor allow the original sedimentary fabrics to be distinguished from those modified by deformation the progressive tectonic modification of these fabrics leads to the concept of fabric evolution paths and the extent of the modification is expressed by a deformation parameter although it is emphasised that this parameter is not solely a function of finite strain magnitude its variation is represented on a map which brings out different degrees of variscan tectonic modification of bedding fabrics this map delineates a variscan bedding fabric front corresponding to the northern boundary of a zone of pervasive and strong deformation in the foreland this new analysis allows the variation of variscan trends to be mapped and the significance of these trends to be quantified in terms of deformation magnitude 1999 elsevier science b v all rights reserved

tio2nanoparticle trails in garnet implications of inclusion pressure induced microcracks and spontaneous metamorphic reaction healing during exhumation a new mechanism of cleaving healing of garnet in metamorphic rocks during exhumation is reported almandine garnet with submicron multiple phase inclusions characteristic of the grail reaction garnet rutile kyanite ilmenite low quartz was found by analytical electron microscopy to have non epitaxial rutile nanoparticles distributed along internal 110 microcrack trails at the acute corner of submicron multiple phase inclusions defined by the intersecting 110 and 011 mould surfaces such garnet microcracks were formed during lithostatic decompression due to a relatively high compressibility of quartz in the inclusion pockets and stress concentration at the acute corner spontaneous healing with accompanied formation of non epitaxial rutile nanoparticles was activated predominantly via the grail reaction due to high surface tension at the tip of microcracks and to a lesser extent decreasing lithostatic pressure or increasing inclusion pressure upon exhumation this new mechanism of microcracking and healing involves stress build up fracture propagation mineral reaction transport of elements to the reaction site and lowering of reaction boundaries by capillarity effect all under the influence of thermodynamic and kinetic factors at the submicron scale thus tio2 nanoparticle trails in garnet provide additional information on the p t path and may shed light on exhumation rates mechanisms and metamorphic reactions processes careful scrutiny of host minerals on the submicron scale is required to tell whether there are other metamorphic reaction facilitated healing processes being overlooked by inappropriate techniques or being obliterated by the predominant healing processes of fluid infiltration and resorption zoning

amazon diversity in light of the paleoecological record abstract disjunct distributions of amazonian species have been explained previously by a refugial theory which postulates that amazonian rain forest was preserved in large highland regions throughout the pleistocene no direct radiocarbon dated evidence exists for the last glacial maximum with which to test this theory the only radiocarbon dates of pleistocene age from the amazon basin are of fossiliferous deposits in the proposed napo refugium of the west where both pollen assemblages and wood samples indicate that forest with cool andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation implying a temperature depression of at least 4 c in the amazon lowlands under modern climatic conditions lateral erosion by river meander together with surface erosion serves as a rejuvenating mechanism for the rain forests of peru and ecuador the instability of late holocene amazonian climates is demonstrated by documenting a precipitation event in the eastern andean cordillera that caused widespread flooding of western amazonian forests 800 1300 bp late holocene pollen histories from widely dispersed parts of central amazonia distinguish between vegetation histories in the drainage of northern south western and western watersheds but all show histories of fluctuating intensities of dry seasons radiocarbon dating of charcoal layers in soils of venezuelan amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka the high species richness of amazonia is a result of numerous opportunities for vicariance because of a very large total area wide variety of habitats and intermediate levels of disturbance particularly by hydrological processes that has varied on timescales from years to millennia amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

late quaternary environmental and climatic changes in central brazil paleoenvironmental changes dating back to 30 000 yr b p documented in a pollen record from central brazil lat 19 s permit the reconstruction of climatic changes related to shifts of the antarctic polar fronts the paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution taking into account present day climatic parameters at 30 000 yr b p the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest from 17 000 to 14 000 yr b p the climate was drier although tree pollen percentages were relatively high after 12 000 yr b p araucaria forest elements increased suggesting a moister and cooler climate the araucaria forest disappeared during a short interval between 11 000 and 10 000 yr b p this could be related to the younger dryas event at the beginning of the holocene the climate became cool and moist again as indicated by the reexpansion of the araucaria forest the latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr b p at 5000 yr b p an arid interval was followed by the expansion of mesophytic semideciduous forest elements

impact of mid to late holocene precipitation changes on vegetation across lowland tropical south america a paleo data synthesis a multi proxy paleo data synthesis of 110 sites is presented exploring the impact of mid to late holocene precipitation changes upon vegetation across southern hemisphere tropical south america we show that the most significant vegetation changes occurred in southwest amazonia and southeast brazil regions reliant on precipitation derived from the south american summer monsoon sasm a drier mid holocene in these regions linked to a weaker sasm favored more open vegetation savannah grasslands than present while increased late holocene precipitation drove expansion of humid forests e g evergreen tropical forest in southwest amazonia araucaria forests in southeast brazil the tropical forests of central western and eastern amazonia remained largely intact throughout this 6000 year period northeastern brazil s climate is antiphased with the rest of tropical south america but a lack of paleo data limits our understanding of how vegetation responded to a wetter drier mid late holocene from this paleo data perspective we conclude that ecotonal forests already close to their climatic thresholds are most vulnerable to predicted future drought but the forest biome in the core of amazonia is likely to be more resilient of greater concern are widespread deforestation and uncontrolled anthropogenic burning which will decrease ecosystem resilience making them more vulnerable than they might be without current anthropogenic pressures

high resolution geochemical record of fluid rock interaction in a mid crustal shear zone a comparative study of major element and oxygen isotope transport in garnet garnet grains from an intensely metasomatized mid crustal shear zone in the reynolds range central australia exhibit a diverse assortment of textural and compositional characteristics that provide important insights into the geochemical effects of fluid rock interaction electron microprobe x ray maps and major element profiles in situ secondary ion mass spectrometry oxygen isotope analyses and u pb and sm nd geochronology are used to reconstruct their thermal temporal and fluid evolution these techniques reveal a detailed sequence of garnet growth re equilibration and dissolution during intracontinental reworking associated with the ordovician carboniferous 450 300 ma alice springs orogeny a euhedral garnet porphyroblast displays bell shaped major element profiles diagnostic of prograde growth zoning during shear zone burial coexisting granulitic garnet porphyroclasts inherited from precursor wall rocks show extensive cation re equilibration assisted by fracturing and fragmentation oxygen isotope variations in the former are inversely correlated with the molar proportion of grossular suggesting that isotopic fractionation is linked to ca substitution the latter generally show close correspondence to the isotopic composition of their precursor indicating slow intergranular diffusion of o relative to fe2 mg and mn peak metamorphism associated with shearing 550 c 5 0 6 5 kbar occurred at c 360 ma followed by rapid exhumation and cooling progressive mn enrichment in rim domains indicates that the retrograde evolution caused partial garnet dissolution accompanying intra mineral porosity production then stimulated limited oxygen isotope exchange between relict granulitic garnet grains and adjacent metasomatic biotite resulting in increased garnet 18o values over length scales 200 m spatially restricted oxygen interdiffusion was thus facilitated by increased fluid access to reaction interfaces the concentration of ca in channelled fracture networks suggests that its mobility was enhanced by a similar mechanism in contrast the intergranular diffusion of fe2 mg and mn was rock wide under the same p t regime as demonstrated by a lack of local spatial variations in the re equilibration of these components the extraction of detailed reaction histories from garnet must therefore take into account the variable length and time scales of elemental and isotopic exchange particularly where the involvement of a fluid phase enhances the possibility of measureable resetting profiles being generated for slowly diffusing components such as ca and o even at low ambient temperatures and relatively fast cooling rates

radiocarbon reservoir effect and the timing of the late glacial early holocene humid phase in the atacama desert northern chile we revise substantially the regional chronology of lake level fluctuations from the late glacial early holocene humid phase along a high altitude transect 3500 to 4500 m between 18 s and 28 s in the southwestern altiplano of northern chile radiocarbon dates and 210pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14c dates our chronology suggests that the latest pleistocene early holocene humid phase started between 13 000 and 12 000 14c yr b p and that maximum lake levels were reached between 10 800 and 9200 14c yr b p this is significantly younger than what has been established so far for the titicaca uyuni basin in bolivia the paleolakes disappeared sometime between 8400 and 8000 14c yr b p our revised chronology agrees with the regional history of human occupation and is broadly synchronous with vegetation changes in subtropical continental south america and with the onset of wetland expansion in the northern hemisphere tropics

holocene dynamics of vegetation change in southern and southeastern brazil is consistent with climate forcing abstract at mid to high northern latitudes postglacial vegetation change has often occurred synchronously over large regions triggered mainly by abrupt climate change based on 19 pollen diagrams from southern and southeastern brazil we explore if similar synchronicities in vegetation change were also characteristic for the vegetation dynamics in low latitudes we used sequence splitting to detect past vegetation change in the pollen diagrams and computed principal curves and rates of change to visually evaluate the changes in composition and dynamics the results show that vegetation change occurred mostly during the second half of the holocene with distinct episodes of change the character of vegetation change is generally consistent with shifts to wetter conditions and agrees with inferred shifts of the south american monsoon speleothems as well as the titanium record from the cariaco basin indicate several episodes of rapid shifts in the precipitation regime which are within the dating uncertainty of the here detected periods of vegetation change 8900 5900 2800 1200 and 550 cal yrs bp our results indicate that low latitude vegetation composition follows precession forcing of the hydrology while change is often triggered and synchronized by rapid climate change much like in high and mid latitudes pollen diagrams document changes in the abundance of individual taxa and changes in the amount of woodland cover while small compositional changes indicate a regional stability of vegetation types during the holocene

fault systems and paleo stress tensors in the indus suture zone nw pakistan abstract analysis of fault striations measured in the kohistan part of the indus suture zone nw himalaya pakistan has been carried out to document dynamic evolution during the brittle stage of the collision of india and asia processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as sse nnw compression e w compression radial extension and ssw nne compression the last corresponds to the present day stress field defined from seismic activity the earlier stress fields are related to times during the miocene when convergence related stresses were disturbed by the formation of the nearby nanga parbat and indus syntaxes

paleoproductivity changes during the holocene in the inner shelf of cabo frio southeastern brazilian continental margin benthic foraminifera and sedimentological proxies abstract sedimentological and benthic foraminifera analyses carried out on a core length 4 15 m collected at 22 56 31 s and 41 58 48 w at a water depth of 43 m sampled from the inner shelf of cabo frio southeastern brazilian continental margin allowed identification of different hydrodynamic and productivity regimes related to sea level fluctuations and or climatic changes during the last 9 4 ka cal bp prior to 7 0 ka cal bp a less intense hydrodynamic and lower productivity regime occurred at lower sea levels and under drier climatic conditions between 7 0 and 5 0 ka cal bp relatively stronger local oceanic circulation and relatively high productivity were observed in a scenario of rising sea levels and more humid conditions from 5 0 to 3 0 ka cal bp bottom currents weakened and input of nutrients increased with productivity levels similar to the previous phase at lower sea level and in a drier climate from 3 0 ka cal bp up to the present stronger hydrodynamic conditions and a higher productivity regime are linked to the establishment of the upwelling process in cabo frio from 2 5 ka cal bp to the present upwelling enhancement has been recognized resulting from the combined action of ne winds and the intensification of the meandering pattern of the brazil current bc

an aem study of garnet clinopyroxenite from the sulu ultrahigh pressure terrane formation mechanisms of oriented ilmenite spinel magnetite amphibole and garnet inclusions in clinopyroxene optical microscopy secondary electron microscopy and analytical electron microscopy were used to characterize crystallographic orientation relationships between oriented mineral inclusions and clinopyroxene cpx host from the hujialing garnet clinopyroxenite within the sulu ultrahigh pressure uhp terrane eastern china one garnet clinopyroxenite sample 2hj 2c and one megacrystic garnet bearing garnet clinopyroxenite rz 11d were studied porphyroblastic clinopyroxene from sample 2hj 2c contains oriented inclusions of ilmenite ilm spinel spl magnetite and garnet whereas clinopyroxene inclusions within megacrystic garnet from sample rz 11d contain oriented inclusions of ilmenite and amphibole specific crystallographic relationships were observed between ilmenite spinel plates and host clinopyroxene in sample 2hj 2c and between ilmenite plates and host clinopyroxene in sample rz 11d i e 1 bar 1 00 ilm 0 bar 1 0 cpx 0001 ilm 100 cpx and 110 spl 0 bar 1 0 cpx bar 1 11 spl 100 cpx these inclusions are suggested to be primary precipitates via solid state exsolutions most of the needle like magnetite spinel inclusions generally occur at the rims or along fractures of clinopyroxene within sample 2hj 2c despite the epitaxial relation with host clinopyroxene these magnetite spinel needles would have resulted from fluid melt infiltrations non epitaxial garnet lamellae in clinopyroxene of sample 2hj 2c were formed via fluid infiltration deposition primarily along 010 and subordinately along 100 partings epitaxial amphibole plates with a thickness 1 m and lamellae with a thickness 1 10 m in host clinopyroxene of sample rz 11d were probably results of hydration processes although amphibole plates could otherwise be interpreted as exsolution products temporal relations between mineral inclusions in each sample can be established and a semi quantitative p t path for this garnet clinopyroxenite body was derived accordingly the present results show that the hujialing garnet clinopyroxenite may not have subducted to mantle depths as deep as 250 km during uhp metamorphism as suggested by previous studies this study demonstrates that the crystallographic and temporal spatial relationships between aligned inclusions and host minerals are essential to a correct genetic interpretation of metamorphic rocks

weathering and morphogenesis in a tropical plateau summary weathering phenomena on the campos do jordao plateau have been analysed in order to show their relationship to geomorphic compartition and morphogenetic dynamics correlations between weathering characteristics of surficial materials and geomorphic compartments are more conspicuous in saprolite than in soils on the plateau highest areas gibbsite is the most important secondary mineral at lower altitudes kaolinite prevails thus the spatial distribution of secondary minerals seems to outline two weathering processes alitization and monosialitization defined and interpreted as two different stages within a general alitic weathering trend on hillslopes bedrock weathering degree reflects the intensity of morphogenetic actions hillslope deposit profiles frequently show degrees and sequences of weathering related to downslope mouvement processes rather than to incipient post depositional pedogenetic activity red ferralitic materials overlaid by superficial podzolized ones point to the superposition of two pedogenetic trends linked to variations in environmental conditions ferralitic materials would be remnants of weathering processes active during the tertiary at lower altitudes prior to the plateau uplift

controls on the erosion of the continental margin of southeast brazil from cosmogenic 10be in river sediments abstract the atlantic ocean coast region of southeast brazil contains two coast parallel mountain ranges the serra do mar and serra da mantiqueira generated by tectonic activity pulses tens of millions years after the main continental rift event occurred around 120 ma although the short term erosion rates for the region are established the relative importance of the factors controlling erosion is poorly constrained we combine new and published catchment averaged erosion rates n 48 using in situ produced 10be concentrations in quartz from river sediments to establish the regional erosion pattern the river catchments are i escarpment topography ii high altitude low relief and iii mixed topography which record how escarpment fronts are migrating inland ocean facing coastal escarpment catchments of the serra do mar e 18 53 m ma can be eroded approximately twice as fast as continent facing escarpment catchments in the serra do mar and serra da mantiqueira e 7 24 m ma the correlation between the normalized channel steepness index ksn and slope angle indicates that river incision and hillslope erosion processes combine to maintain the high relief the serra do mar catchments define a mean slope angle threshold indicating that landslides are the dominant erosional process when slope angles in excess of 30 tectonic activity is low and plays no significant role in driving erosion a first order relationship between erosion rate and precipitation temperature across the region implies that climate plays a key role in soil production river incision and in triggering erosional processes although the high topographic relief is a pre condition for the occurrence of significant erosion the climatic condition is the outlining factor of the regional variation in erosion rates

related changes in biodiversity insolation and climate in the atlantic rainforest since the last interglacial abstract the long term colonia record is located in the atlantic rainforest domain in brazil 23 52 s 46 42 20 w 900 m a s l the 780 cm long core co3 provides a coverage of a complete interglacial glacial cycle for the first time in a neotropical rainforest information on the behavior of tropical climates compared to global changes in temperatures indicates specific climate responses in terms of precipitation at these latitudes winter extratropical circulation was very active during the last interglacial and most of the glacial floristic composition of the rainforest changed several times in each phase of expansion twice during the interglacial and three times during glacial episodes araucaria was well developed in the area of sao paulo until the beginning of the first dry phase of the glacial at ca 50 000 yr b p changes in insolation controlled the expansion of the rainforest and the tropical hydrological cycle as evidenced by a strong precession signal however precession had no impact on regional climatic features the two interglacials mis 5e and holocene showed completely different patterns attesting to the continuous evolution of the forest the biodiversity index shannon wiener index remained high during both the interglacial and glacial attesting to the permanence of small patches of rainforest refugia during drier phases the lowest shannon wiener indexes were recorded between 23 000 and 12 000 yr b p and 40 000 and 30 000 yr b p and characterize two marked phases of stress for the rainforest

what the past can say about the present and future of fire wildfires are an integral part of most terrestrial ecosystems paleofire records composed of charcoal soot and other combustion products deposited in lake and marine sediments soils and ice provide a record of the varying importance of fire over time on every continent this study reviews paleofire research to identify lessons about the nature of fire on earth and how its past variability is relevant to modern environmental challenges four lessons are identified first fire is highly sensitive to climate change and specifically to temperature changes as long as there is abundant dry fuel we can expect that in a warming climate fires will continue to grow unusually large severe and uncontrollable in fire prone environments second a better understanding of slow interannual to multidecadal socioecological processes is essential for predicting future wildfire and carbon emissions third current patterns of burning which are very low in some areas and very high in others are often unprecedented in the context of the holocene taken together these insights point to a fourth lesson that current changes in wildfire dynamics provide an opportunity for paleoecologists to engage the public and help them understand the potential consequences of anthropogenic climate change

a plea for more caution in fault slip analysis abstract the analysis of fault slip data is a widely used tool in structural geology this method consists of three major steps a data acquisition by measurements in outcrops b data separation into homogeneous subsets and calculation of the principal stress or strain axes with one of several available methods and c data interpretation in a regional tectonic context which includes the assignment of ages and the derivation of regional patterns each one of these three steps may introduce artefacts and misinterpretations the major problem during step a is sampling bias due to unfavourable outcrop geometry or due to neglecting faults with subtle slip sense indicators step b contains numerous possibilities to influence the calculation results e g by arbitrary separation of data into subsets choice of the analysis method and uncritical use of software age assignment in step c can in most cases be made only indirectly e g by the assumption that measured outcrop scale faults have the same age as parallel map scale faults or by the inference that subsets from different sites with parallel oriented principal axes are syngenetic neither assumption is necessarily valid with this paper we want to sharpen researchers awareness of the problems related to fault slip analysis

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them