a facies analysis of the pucara group norian to toarcian carbonates organic rich shale and phosphate of central and northern peru reply abstract the pucara group contains an excellent record of marine uppermost triassic and basal jurassic sedimentation new biostratigraphic and lithostratigraphic studies have led to a reassessment of the regional internal correlation of the group and thus to a new understanding of the facies relationships there is a relatively complete record of sedimentation from late norian to late early jurassic the only notable omissions apparently occurring in the latest norian and at the hettangian sinemurian boundary the oldest constituent formation the chambara which is locally of great thickness consists largely of dark cherty limestones representing basinal conditions of sedimentation the succeeding aramachay formation marks widespread recommencement of sedimentation in the semicostatum zone of the sinemurian with organic rich shales passing up into phosphatic deposits it is proposed that this event is the consequence of a significant eustatic rise of sea level the record of sedimentation of the youngest condorsinga formation is restricted to central peru and no other middle upper lias units are identified alternating marginal marine and shallow neritic conditions are inferred with high carbonate production rates and dolomitizing environments the character of the sediments particularly the phosphatic deposits suggests a tectonically quiescent continental margin with unrestricted access to the palaeo pacific ocean in contrast to earlier palaeogeographic interpretations as such the pucara group represents unusual conditions in the development of the andean regime

strain patterns decollement and incipient sagducted greenstone terrains in the archaean dharwar craton south india the archaean dharwar craton is characterized by two greenstone successions the 3 ga sargur group and the 3 0 2 5 ga dharwar supergroup examples of both successions are described from the region of jayachamarajapura where they are also distinguished by different tectonic patterns the younger greenstones have undergone only minor deformation and are only slightly metamorphosed and so provide a good case study of the relative behavior of greenstones in relation to their granite gneiss country rocks a detailed structural analysis indicates two strain fields associated with two deformational episodes d1 and d2 the d1 episode produced dome and basin structures and affected merely the older greenstones and the gneisses the mapped strain field is compatible with the hypothesis that it is associated with the development of diapiric type gravitational instabilities the d2 episode affects only the younger greenstone belt which has the overall geometry of a complex syncline it is discordant over a complex of gneisses and older greenstones that was deformed during the d1 episode the base of the discordant cover sequence is tectonized and constitutes a decollement surface kinematic criteria at this surface have opposite sense and converge towards the belt axis these structural features are interpreted in terms of progressive deformation compatible with the incipient development of a sagducting trough these results are consistent with those obtained from other parts of the craton where the tectonic evolution appears to reflect mainly relative vertical displacements facilitated by the reheating of continental crust during two major archaean tectonometamorphic episodes copyright 1996 elsevier science ltd

structural tests of diapir hypotheses in archean crust of ontario detailed structural maps of two granitoid complexes in the wabigoon subprovince are used to test three diapir hypotheses advanced in earlier papers the gneiss masses of and individual domes within the complexes fail the test for solid state diapirism the gneiss domes also fail the test for tensile bending caused by hypothetical magmatic diapirs in the subsurface an oval pluton located near the best exposed gneiss dome proves to be a synformal sheet rather than a funnel shaped magmatic diapir this pluton could be a syenite diorite phacolith emplaced into a concordant zone of dilation during the late upright folding of the gneiss mass about horizontal axes earlier tight folds were probably recumbent and south verging and like the gneissosity generated in a ductile shear regime with subhorizontal glide planes these observations have important implications for archean tectonics especially the relative horizontal displacement of large greenstone masses potentially allochthonous greenstone belts

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

sedimentary dynamics of the kimmeridge clay tempests and earthquakes storms are suggested to be an important influence upon the formation of epicontinental black shales controlling both their distribution and facies types a variety of storm produced event beds are described from the kimmeridge clay of dorset these include horizons of graded rip up clasts silt laminae thin graded mud horizons and shell pavements biostratinomy and population dynamics indicate that the pavements represent brief benthic colonization events in a predominantly anaerobic dysaerobic environment differential near surface lithification has also affected the sediments leading to the formation of flow phenomena these include loop structures microfolding and brecciation earthquake induced fissuring also occurs at a number of horizons the kimmeridge clay shows well developed cyclically alternating organic rich shales and mudstones on a decimetre scale a feedback mechanism of storm induced benthic oxygenation and temperature stratified inhibition of storm mixing may account for the abrupt nature of the cyclicity subsidence and sedimentation rate were probably important factors controlling the thickness and organic richness of the sediments whilst the influence of storms was important in controlling the distribution and facies types of these important source rocks the model proposed for the kimmeridge clay may be of general application to many epicontinental black shales in the geological record

evolution of upwelling in the atlantic ocean basin understanding the evolution of the surface circulation and the patterns of upwelling in the atlantic is important not only because of the ocean s crucial role in the present day thermohaline circulation in supplying heat to high latitudes but also because of the significant petroleum reservoirs found around the basin in this paper we examine the upper ocean circulation during four time slices the kimmeridgian c 155 ma the cenomanian c 100 ma the maastrichtian c 70 ma and the early eocene c 50 ma using a 1 5 layer reduced gravity ocean model for each time slice the upwelling fields predicted from simulations of wind driven upper layer circulation are compared with the deep sea and continental margin sedimentary records the boundary configurations at each time slice are the subject of sensitivity tests where matching of both deep sea and coastal sedimentary records with the model predicted upwelling fields is used to suggest best fits between model and geological data our model runs are consistent with there being a deep water connection to the pacific at each time period after the kimmeridgian with such a link being most important to the geological ocean model match in the maastrichtian no period after the kimmeridgian produced a stable ocean simulation with a deep water connection to tethys our simulations c 100 ma suggest that a deep water connection between the north and south atlanctic was not established until after the cenomanian all time slices show a clear western boundary current in the north atlantic although generally only a third to half the strength of today s a similar difference is found between tropical palaeo productivity at each run and today s more productive atlantic ocean we conclude that upwelling and anoxia are not necessarily independent means of producing organic rich marine sediments most such sedimentary deposits laid down during the four time slices can be linked to the presence of upwelling zones thus where anoxia is well established we suggest that upwelling may help supply organic material to the de oxygenated bottom waters

strain patterns in models of spreading gliding nappes three experiments have been carried out in order to study the progressive and finite strain in nappes where gravitational spreading and gliding occur together these experimental models were made from analogue materials able to collapse under their own weight on an inclined plane throughout most of the models the stretch trajectories in a vertical plane parallel to the flow show a low amplitude sigmoidal pattern consistent with a previous theoretical model other stretch trajectories exist at the front and back ends of each model the kinematic significance of all these trajectories is discussed in detail highest strain intensities are always found next to the base of the model strain paths calculated at different stages of flow indicate clearly that nowhere in the model is the motion simple there is a complex combination in time and space of simple and pure shear except at the base of the model where the motion approximates a simple shearing near the two parallel lateral sides of the model a lateral boundary effect can be observed from the strong curvature of the transverse markers surface grid and vertical layers strain paths have also been estimated in this complex zone where wrench shearing is superimposed upon vertical shortening and thrust shearing the geological implications of these experimental models are discussed in relation to recent theoretical studies and field work

identifying regional dust transport pathways application of kinematic trajectory modelling to a trans tasman case pi kinematic trajectory model is used to investigate potential pathways of dust transport from australia to new zealand historically these have been assumed to follow rather direct west east trajectories spanning 2 to 3 days often resulting in red snow events in the southern alps of new zealand however results from the present study which examined the route taken by air parcels originating in southern australia during dust storms on 24 and 25 may 1994 indicate that trans tasman dust transport trajectories are more diverse than previously thought and display considerable variation during single events these mon divergent pathways tie in more closely with aeolian dust sedimentation patterns identified by ocean coring in the tasman sea and may account for the deposition of australian dust on sub antarctic islands located well south of the australian continent copyright 2000 john wiley sons ltd

application of backscattered electron imaging to the study of source rocks microtextures abstract scanning electron microscope sem used in backscattered electron bse mode is a powerful tool for the sedimentological study of source rocks owing to its spatial and chemical resolutions ease and speed of operating the obtained imaging is dependent on atomic number contrasts between the different constituents of the sample using the bse mode combined with energy dispersive x ray spectrometry minerals and organic matter can be distinguished more clearly than with the light microscope classically used by organic petrologists in order to describe microtextures of organic rich sediments particularly the disposition of the organic matter this technique has been tested on source rocks having various sedimentological and geochemical characteristics accordingly two patterns of organic matter disposition have been recognized laminated and particulate these dispositions can be put back into their sedimentary context by considering the depositional environment and diagenesis the organic matter disposition suggests the existence of organic networks which are suspected to be a major control for hydrocarbon expulsion

forest disturbance in the central north island new zealand following the 1850 bp taupo eruption the 1850 bp taupo eruption covered c 30 000 km2 of the central north island with airfall deposits and c 20 000 km2 with ignimbrite this paper reviews pollen and charcoal analyses of lake and peat sediment cores from sites at various distances and directions from the taupo vent to establish the effects of this eruption on the surrounding forests forests within range of the ignimbrite were destroyed and forests located up to 170 km east of the vent suffered variable degrees of damage from ashfall stands of pteridium esculentum and other seral taxa flourished immediately after the eruption fires occurred during the eruption and continued for several decades after the degree and nature of vegetation disturbance above the taupo tephra varied according to the thickness of ashfall local topographical features and probably the vigour of the forest revegetation was complete within 200 years of the eruption even at sites overwhelmed by the taupo ignimbrite post eruption forests were similar to those exi

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

local and regional scale impacts of the 74 ka toba supervolcanic eruption on hominin populations and habitats in india abstract the toba supervolcanic eruption of 74 000 years ago is argued to have devastated homo sapiens populations causing a human population bottleneck through a combination of rapid global climatic deterioration and ecological disruption following the widespread ash fall this dramatic eruption the largest in at least the last 2 million years is hypothesized to have shaped the genetic structure and diversity of human populations today past assessments of toba s human impacts however have been predominantly theoretical using archaeological and geological evidence from sites in india this study addresses toba s local scale impacts on hominin technology behavior demography and habitats in two valleys in india the jurreru and middle son valleys using paleoclimatological and volcanological data regional scale impacts throughout india are inferred a refugia hypothesis is presented that argues for variation in the scale of toba s impact throughout india driven by regional differences in monsoonal dynamics geography and topography areas of north west india the indo gangetic plain and parts of the deccan to the east of the western ghats are argued to have been the most affected whereas areas of southern and eastern india may have preserved the largest refugia for hominin populations

signals of watershed change preserved in organic carbon buried on the continental margin seaward of the waipaoa river new zealand abstract holocene sediments buried on the continental shelf seaward of the waipaoa river northeastern new zealand preserve a stratigraphic record of terrestrial environmental change the well characterized long term record of storms volcanism and human disturbance in this region provides an opportunity to examine how such changes are reflected in the character of organic carbon oc buried on the continental margin complimentary evidence obtained from analyses of the 14 c content and the elemental and stable carbon isotopic composition of different sedimentary fractions including charcoal wood and clay sized isolates indicates that these perturbations led to mobilization of oc components with variable storage histories in the watershed charcoal transported in the modern waipaoa river and buried in offshore depocenters includes a highly aged component that has apparently been slowly released from storage in soil or alluvial terraces the charcoal fraction ages become dramatically younger in sediments deposited after the taupo volcanic eruption 1717 cal yr bp and then polynesian settlement ca 700 cal yr bp both signaling biomass burning the mean age of woody plant fragments and clay bound oc deposited on the shelf also varies over time with older material having accumulated in the middle holocene and since human occupation deposition of older than average wood fragments and clay bound oc between about 5 and 3 6 kyr bp correlates with evidence for a period of increased storm frequency in the region and may reflect the enhanced delivery of aged soil and sedimentary rock mobilized from hill slopes via earthflows and or deep seated landslides similarly the deposition of older wood and clay bound oc commensurate with the first anthropogenic disturbance ca 700 years ago is consistent with accelerated mass wasting due to deforestation at the same time a change in the elemental and stable isotopic composition of bulk and clay bound oc buried on the shelf may reflect increased marine primary productivity and or mobilization of oc from deep levels in soil profiles deforestation of the waipaoa headwaters by european settlers beginning in the middle 19th century is evinced by a sharper rise in the age of clay associated oc buried offshore today deep gully incision into fractured sedimentary bedrock is a major source of sediment and kerogen to the river and this process has left its mark on the age of sedimentary oc delivered to the adjacent margin

diapirism bulk homogeneous shortening and transcurrent shearing in the archaean dharwar craton the holenarsipur area southern india abstract qualitative strain data are spatially integrated in order to define archaean foliation trajectories and variations in strain intensity and ellipsoid type in the holenarsipur area dharwar craton southern india the study provides constraints on the bulk geometry the progressive deformation and the kinematic history of this region of archaean continental crust two major structural events have shaped the study area i a regional diapiric event contemporaneous with a magmatic event and ii a later sinistral transcurrent ductile shear event which has locally reoriented both foliations and stretching lineations the entire holenarsipur supracrustal belt underwent a common tectono metamorphic history that included two metamorphic events each event corresponds temporally to a distinct strain field the first a regional amphibolite facies event was contemporaneous with the main tectonic event and probably with the intrusion of halekote trondhjemites the second occurred under greenschist facies conditions and was restricted to a late transcurrent shear zone at the eastern boundary of the greenstone belt the strain pattern prior to transcurrent shearing cannot be explained by a thrusting event unless all trace of this event had been erased by the diapirism we interpret all structures older than the transcurrent shearing to be the direct result of vertical movements linked to body forces augmented by minor horizontal crustal shortening

evidence for continued disturbance of upland rain forest in sumatra for the last 7000 years of an 11 000 year record abstract a pollen diagram is presented from a swamp at 1100 m altitude in the sumatran rift valley indonesia the diagram covers the last 11 000 years and shows evidence of continuous cover by tropical rain forest there are indications of continuous disturbance probably by people during the last 7000 years this has caused little change in diversity which does not support the intermediate disturbance hypothesis of connell science 199 1978 1302

mapping and geochemical characterization of the toarcian organic matter in the mediterranean tethys and middle east organic matter from toarcian outcrops and boreholes in several basins around the mediterranean sea and middle east has been studied rock eval pyrolysis elemental analyses of kerogens and gas chromatography of chloroform extracts within these different basins have been used to determine the amount petroleum potential and type of the organic matter the results have been used to compile a mapping of the organic matter for the toarcian stage which shows heterogeneities in the distribution and type of organic matter 1 1 marine organic matter type ii occurs in different environments of deposition whereas high contents 5 total organic carbon correspond to thick deposits within the west european realm great britain north sea paris basin and germany the organic matter is less abundant in the mediterranean area where lower concentrations 1 2 toc preserved in lower toarcian thin levels are limited only to restricted basins northern italy greece 2 2 the predominance of continental organic matter type iii along the northern margin of the tethys corresponds to a deltaic environment 3 3 there is a predominance of altered organic matter within the carbonated platforms around the mediterranean tethys these results supplemented with the data issuing from the literature add a geochemical dimension to the paleogeography of the tethys

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

strain patterns in archaean dome and basin structures the dharwar craton karnataka south india abstract models simulating the role of gravity in the earth s crust are the main source of criteria used for the field identification of diapirs after a short review of the distribution of finite strain in experimental diapir models we describe an example where differential erosion of a tilted craton has provided 3d geometrical information on patterns in a diapiric system at various depths from greenschist to granulitic facies conditions within the archaean continental crust of the dharwar craton south india diapirs and anti diapirs sagducted greenstones are observed at different levels structures and strain are consistent with all the field identification criteria inferred from experimental simulation but some peculiar structural features are also observed which are not predicted by the models these features such as strain trajectory triple junctions result from i the progressive deformation of diapiric domes or sagducted basins ii interferences between diapiric structures body forces and iii the superimposition of diapiric strain fields on regional horizontal shortening boundary forces

last glacial maximum to early holocene wind strength in the mid latitudes of the southern hemisphere from aeolian dust in the tasman sea dust transported by southern hemisphere mid latitude westerly winds from australia and deposited in the tasman sea shows no evidence for stronger winds during the last glacial maximum lgm compared to the holocene features of the particle size distributions of the dust do however indicate enhanced dry deposition of dust in the lgm changing to rainfall scavenging during deglaciation and the early holocene as climate ameliorated from these results it appears that activation of desert dunefields over 40 of australia during the lgm was the result of a reduction in stabilizing vegetation and more frequent episodes of sand movement rather than of increased wind strength the lgm climate of inland australia must have been considerably more stressful for plants as a result of lower precipitation and or carbon dioxide stress to achieve the implied levels of surface destabilization enhanced atmospheric dust loads in the southern hemisphere and deposition over antarctica were most likely the result of greatly expanded source areas in the mid latitude southern continents and a weaker hydrological cycle rather than greater entrainment or more efficient transport by stronger winds during the lgm wind strength appears to have varied regionally and predominantly in high latitudes rather than uniformly for all zonal winds

sedimentological evidence concerning the paleoceanography of the cretaceous western north atlantic ocean abstract black clays developed as a result of progressively intensifying intermittent anoxic conditions from the early through mid cretaceous the preservation of primary sedimentary structures of authigenic minerals such as pyrite and siderite and of significant amounts of organic carbon testify to the stagnant conditions intermittent anoxic conditions prevailed in the deepest portion of the basin resulting from vertical migration of an intrasediment anoxic interface middle aptian variegated clays within the black clay sequence at several low latitude sites suggest a widespread oxygenation event of short duration occurred there greater thicknesses of black clays accumulated in low latitudes implying that surface or intermediate depth currents redistributed the sediments south ward millimeter scale laminae characterizing the early and mid cretaceous sediments represent seasonal sediment input where seasons during the cretaceous had durations measured in years cenomanian variegated clays succeeded the black clay interval and represent deposition under totally oxygenated conditions thus the sluggish and stagnant conditions present in the early and mid cretaceous were followed by increased current activity these currents were derived from more northern latitudes as iberia was rifted from north america cooler temperatures presumably increased the oxygen capacity of the water and its ability to sink into the deep basin to relieve the stagnant conditions present the late cenomanian through late campanian was a time of widespread marine transgression resulting in the deep ocean becoming a sediment starved basin clastics and carbonates accumulated on the shelves as the calcite compensation depth ccd shallowed appreciably the late campanian through maastrichtian interval is characterized by calcium carbonate accumulation throughout much of the deep basin a significant lowering of sea level paralleled by a deepening ccd caused this sedimentation pattern

environmental change in northland new zealand during the last glacial and holocene abstract the quaternary vegetation and climatic history of the northernmost region of new zealand northland has long been the subject of speculation although the coverage is incomplete and individual records are punctuated by gaps or marked changes in sedimentation rates poor resolution and dating uncertainties recent work points to environmental changes that differ significantly from those at higher latitudes in new zealand conifer angiosperm forest has been important in northland during most of the last glacial cycle with agathis australis and nothofagus truncata dominated communities prominent during interstadials and stadials respectively fire and effective precipitation appear to have exerted greater influence on vegetation developments than temperature although the latter may control the competitive balance between agathis and nothofagus and will influence the environmental response to precipitation changes with the exception of human impacts during the last millenium the most striking vegetation changes are associated with widespread fires towards the end of the last glacial and the moist preceding interstadial in contrast pre human era holocene environments have been comparably stable although there is some evidence for increasing natural disturbance and a drier slightly cooler climate during the late holocene in several key aspects a glacial maximum to lateglacial dry phase very moist interstadial preceding the last glacial maximum no widespread loss of forest and the importance of fire and precipitation change in vegetation development during the last glacial cycle generally northland shows stronger affinities with south eastern australia than with other regions in new zealand

interference between pluton expansion and non coaxial tectonic deformation three dimensional computer model and field implications abstract structures in orogenic belts are greatly controlled by interactions between pluton related and tectonic related strain fields however many aspects of the geometry and evolution of these structures are poorly known for example 1 what is the geometry of these structures if regional deformation is coaxial 2 how does this geometry change with progressive deformation this paper describes a three dimensional simulation of strain shape and magnitude as well as foliation and lineation patterns formed by interactions between pluton expansion and homogeneous coaxial deformation this simulation suggests that interactions between pluton expansion and regional uniaxial shortening generate patterns that are distinct from the patterns produced by regional uniaxial extension or regional non coaxial deformation for example shortening produces doughnut shaped constrictional rings about the pluton whereas extension produces apple shaped flattening regions around the pluton in addition shortening produces one continuous doughnut shaped low strain region around the pluton on the other hand extension creates two separate ellipsoidal low strain regions at the ends of the pluton furthermore shortening forms foliation rings that have triangular two dimensional sections and lineation is concentric around the axis of maximum shortening in contrast extension produces two separate foliation and lineation cones at the ends of the pluton all these structural and strain elements migrate away from the pluton with increasing expansion rates and towards the pluton with increasing tectonic deformation rates although structural studies around plutons should always integrate microstructural radiometric and field measurements simulation generated patterns can be used to evaluate 1 origin geometry and evolution of structures around plutons 2 mechanisms that explain inclusion trails within porphyroblasts 3 contribution of pluton related strains to strains measured in the country rock and 4 type and three dimensional orientation of regional kinematic schemes

annual layering in the upper jurassic kimmeridge clay formation uk quantified using an ultra high resolution sem edx investigation abstract this paper reports the results of an ultra high resolution investigation of the geochemistry of the late jurassic kimmeridge clay formation kcf using scanning electron microscope energy dispersive x ray analysis sem edx sub millimetre banding is revealed in which each band approximately 112 m thick comprises a couplet of coccolith rich and coccolith poor sediment major element analysis reveals that regularly spaced peaks in the relative amount of calcium are associated with coccolith rich bands it is argued that each couplet represents an annual layer the calcium peaks corresponding to an annual bloom of coccolithophorids there is also a broad correlation between the calcium aluminium ratio and the ratios of sodium aluminium phosphorus aluminium and potassium aluminium to calcium aluminium ratios we tentatively suggest that there may be a link here sodium phosphorous and potassium today being key nutrients for coccolith productivity aluminium is taken as representing the background terrigenous clay fraction if each banded couplet is indeed annual and if the thickness of such bands were to be representative of the kcf as a whole then the post compactional thickness is broadly in agreement with sedimentation rates of 100 m per year calculated by oschmann 1990 this study confirms the view that the kcf in southern england accumulated in a predominantly anoxic environment that favoured the preservation of organic material within the bottom sediment bundles of bands clustering in groups of about 8 10 are tentatively related to short term changes in insolation possibly sun spot cycles

using rat gnawed seeds to independently date the arrival of pacific rats and humans in new zealand the pacific rat rattus exulans was transported throughout the south pacific with voyaging humans thus the earliest dated evidence of pacific rat can be used to infer first human contact until recently it was considered that rats arrived in new zealand with humans in the thirteenth century ad however controversial radiocarbon dates on pacific rat bones now suggest that rats reached the remote islands of new zealand with people c ad 50 150 these dates are anomalous because they imply human contact with new zealand more than 1000 years before any archaeological evidence for human presence and precede settlement of tropical eastern polynesia the ancestral homeland of maori the first new zealanders the early rat bone dates are controversial for other technical reasons which have been debated in the literature here distinctive rat gnawed seed cases preserved in sediments are used as a proxy to independently date the arrival of the pacific rat and humans in new zealand this method effectively b

an integrated environment analysis lithofacies chemofacies biofacies of the oligocene calcareous siliciclastic shelf deposits in northern germany during the oligocene monotonous fine grained siliciclastic and calcareous shelf sediments of the septaria clay fm were deposited in the north german basin the uniform grain size spectrum and the homogeneous outward appearance of these sediments forces environmental analysis to be based on a joint investigation of the inorganic and organic facies the transgression of the rupelian sea caused tidal sand sheets to form off the mouth of estuaries upon deepening of the basin the benthonic oxygen content of the bottom water diminished and inner shelf muds were deposited following this early transgression a conspicuous change may be recognized when a siliciclastic shelf was replaced by a calcareous siliciclastic shelf upon shoaling of the basin and warming of the seawater these outer shelf conditions persisted until fine grained clastic sediments became more and more dominant during the early late oligocene their depositional environment may be described as shallow lagoon in the succeeding formation of the oligocene tidal bars and estuarine sands are characteristic the uppermost formation penetrated by the drill hole in the gartow area contains estuarine channel sands in conclusion the oligocene sedimentary record reflects a symmetrical facies pattern showing calcareous siliciclastic cyclothems in the central section and siliciclastic shelf deposits below and above reflecting the cyclical nature of the oligocene sea in a dominantly tidally influenced depositional environment the use of clay minerals heavy minerals carbonates phosphates and sulphides together with dinocysts nannofossils and foraminifera has proved to be a successful tool in palaeoecological and palaeoenvironmental analyses

origin of mid cretaceous black shales in the benue through nigeria abstract black and dark gray laminated shales with large amounts of both terrestrial and marine organic material are common in upper cenomanian to lower santonian rocks of the benue trough these shales were deposited during global mid cretaceous marine transgressions when widespread high organic carbon sedimentation took place the benue trough in those times was the site of a shallow density stratified anoxic epeiric sea with estuarine type circulation from this reservoir nutrient rich oxygen depleted waters were fed into the northern parts of the south atlantic ocean

stream functions and complex potentials implications for development of rock fabric and the continuum assumption abstract stream functions may be applied to study the development of ductile deformation patterns in rocks it is demonstrated how to derive the stream function and the associated complex potential from the velocity field of any particular flow finite deformation patterns are subsequently modelled analytically from this mathematical description of flow basic examples discussed are rigid body translation pure shear and composite flows due to simultaneous pure and simple shear a general stream function is obtained to describe the flow regime within a ductile deformation zone deforming by homogeneous plane strain by superposed pure and simple shear components the deformation patterns are visualized using analytical methods only the results are discussed in terms of fabric formation progressive deformation in a simple continuum modelled here mathematically using principles of fluid mechanics is compared with crystalline creep in rocks the validity of the continuum assumption is briefly outlined in view of recent experiments on particular synthetic monocrystalline aggregates octochloropropane ocp deformable at room conditions this provides a method for testing how crystalline deformation compares with an isotropic continuum

three dimensional field perspective on deformation flow and growth of the lower continental crust dharwar craton india 1 the study of fabric development and juvenile batholith emplacement across the tilted crustal section of the eastern dharwar craton shows that horizontal constrictional deformation affected large volumes of the midcrust and lower crust at the time of regional partial melting and magmatic accretion constriction is achieved by a combination of coeval shallow and steep planar fabrics sharing a common horizontal elongation direction two sets of conjugate strike slip shears and extensional shear zones the eastern dharwar craton illustrates an end member deformation mode by which a particularly weakened lithosphere responds to shortening by developing distributed horizontal plane strain on a crustal scale resulting from the combination of crustal shortening and lateral gravity driven flow thinning accompanying constrictional deformation is interpreted as compensating for juvenile magmatic accretion and thickening of greenstone belts and as acting to maintain a stable crustal thickness such a midcrustal to lower crustal deformation process may provide a resolution of the batholithic room problem in a softened crust submitted to lateral shortening and may explain nearly isobaric retrograde pressure temperature time paths of high temperature low pressure high grade terrains

pliensbachian toarcian ostracod biogeography in nw europe evidence for water mass structure evolution abstract this paper examines the role played by palaeoceanographic and climatic conditions on the palaeobiogeography of the pliensbachian toarcian ostracods early jurassic in the european epicontinental sea ees the influence of the palaeogeography ocean currents and sea level temperature and salinity variations on ostracod abundance diversity and migration patterns is reconstructed ostracod migration follows an anticlockwise circulation in the eastern side of the ees with a leading northeast southwest movement and the frequent arrival of tethyan faunas into the central and western parts of the ees during the pliensbachian a three fold classification of water masses based on salinity temperature lithological and fossil data is proposed the repeated inflow of tethyan ostracods into the ees ended by the earliest toarcian this ostracod event is related to the opening of the hispanic corridor and to the reorganization of the surface and deep circulations that may have generated a cold episode at the beginning of the toarcian

the end triassic bivalve extinction event one of the most important episodes of mass extinction of animal groups in the whole of the phanerozoic took place in the latter part of the triassic but the time of major faunal turnover of the vertebrates preceded that of marine invertebrates by several million years as shown by ammonites brachiopods and conodonts decline from a carnian early norian diversity peak was followed by a significant extinction episode at the end of the period this pattern is confirmed at generic and subgeneric level by the bivalve molluscs probably the most abundant and diverse macroinvertebrate group this paper analyses the bivalves in detail and attempts to seek a relationship of the extinction event to environmental changes as recorded by late triassic facies stratigraphy of the youngest triassic is briefly discussed following a recent recommendation the rhaetian stage is dropped and the upper norian sevatian subdivided into three new ammonite zones it is suggested that the classic northwest european rhaetic correlates with the kossen and zlambach beds of the alps and corresponds at least approximately with the upper two of these zones it is estimated that nearly half the existing bivalve genera and nearly all the species failed to survive the end triassic extinction event the trigonioid unionoid and hippuritoid orders were especially strongly affected but most of the pholadomyoid genera survived three major ecological categories are distinguished a shallow neritic group to which most taxa belong a euryhaline group that could tolerate marginal marine and lagoonal conditions and a deep neritic group notably halobia and monotis all groups were strongly affected by the extinction but species of the deep neritic group were apparently the most susceptible seven biogeographic regions are distinguished for the purpose of analysis and it is shown that provinciality is slight but some important taxa are endemic to the tethyan and pacific regions endemic genera prove to have been much more subject to extinction than cosmopolitans there are very few places in the world with a more or less continuous marine sequence of deposits across the triassic jurassic boundary details are given of sections in the alps northwest europe and nevada and briefer mention made of others with regard to late triassic palaeogeographic changes those involving climate were neglibible but there was a more or less progressive regression of epicontinental seas following a ladinian early carnian transgressive maximum with a corresponding shallowing in the more continuously marine tethyan region that this first order effect was due to a eustatic lowering of sea level is fairly certain but the situation is less clear for second order transgressive regressive cycles the late late norian rhaetian cycle is probably however the results of a minor eustatic event by the end of the triassic the sea had regressed substantially and the mass extinction event is though to be bound up partly with this phenomenon and partly with the phase of widespread anoxicity that occurred during the succeeding hettangian transgression

evolution of the sedimentary system beneath the deep pacific inflow off eastern new zealand results from ocean drilling program sites 1121 1124 show the eastern new zealand oceanic sedimentary system enzoss evolved in response to 1 the inception of the circum antarctic circulation 2 orbital and non orbital regulation of the global thermohaline flow and 3 development of the new zealand plate boundary enzoss began in the early oligocene following opening of the tasmanian gateway and inception of the ancestral antarctic circumpolar current acc and sw pacific deep western boundary current dwbc widespread erosion marked by the marshall paraconformity was followed by extensive drift formation in the late oligocene early miocene alternating nannofossil chalk and nannofossil rich mud deposited in response to 41 kyr orbital regulation of the abyssal circulation with the mudstones representing times of increased inflow of corrosive southern source waters drift deposition at the deepest sites was interrupted by bouts of erosion coincident with mi1 5 isotopic events signifying expansions of the east antarctic ice sheet and enhanced bottom water formation by late miocene times the basic enzoss was established south of bounty trough the energetic acc instigated an erosional low depositional regime to the north where the dwbc prevailed orbitally regulated drift deposition continued increased convergence at the new zealand plate boundary enhanced the terrigenous supply but little of this sediment reached the deep enzoss as the three main sediment conduits solander bounty and hikurangi channels had not fully developed the plio pleistocene heralded a change from a carbonate to terrigenous dominant supply caused by interception of the dwbc by the three channels 1 6 ma for bounty and hikurangi time of solander interception unknown the solander and bounty fans and hikurangi fan drift systems formed and drifts downstream of those systems received terrigenous detritus supply increased with accelerating uplift along the plate boundary but delivery to the dwbc was regulated by eustatic fluctuations of sea level times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased bounty solander or reduced hikurangi in highstands in glacial times sediment was entrained by a dwbc invigorated by an increased input of antarctic bottom water the acc also accelerated under strengthened glacial winds thus glacials were times of optimum sediment supply to enzoss depocentres where depositional rates were 2 3 times more than interglacial rates

a zoned low p high t complex at the level of anatexis structural and plutonic patterns in metasediments of the archean yellowknife supergroup near bathurst inlet n w t canada abstract within metagreywackes and schists of the archean yellowknife supergroup the development of an anatectic stratigraphy during the late stages of regional deformation has resulted in the formation of a complex with a metamorphicplutonic structural zoning similar to that occurring in phanerozoic low p high t terrains from bottom to top the stratigraphy consists of 1 small folded migmatite grading with decreasing partial melting to 2 sillimanite schist strongly strained by the emplacement of two mica granites 3 andalusite cordierite schist the site of large folds related to the emplacement of the complex each zone is characterized by a different structural style resulting from the interplay between metamorphic grade and deformation for instance in the sillimanite zone the structure was influenced by the extraction of syntectonic melt and its emplacement into fractures at low effective pressure this zone was also the ductile envelope into which sills and plutons of two mica granites derived from the lower migmatites migrated the time taken for evolution of the complex has been constrained by u pb zircon and monazite dating of a member of the early tonalite diorite suite and members of the two mica granite suite this shows the evolution of the complex was rapid ca 10 ma but possibly polyphase the formation of a distinctively styled complex accompanied by syn tectonic anatexis and plutonism may be typical of lower crustal levels of the yellowknife supergroup and other low p high t terrains

new pollen sedimentary and radiocarbon records from the marquesas islands east polynesia implications for archaeological and palaeoclimate studies three sediment cores from one upland and two lowland sites on nuku hiva marquesas islands provide a c 750 year record of palaeo environmental change on the island accelerator mass spectrometry ams dating of pollen concentrates from the base of each core indicates that the three widely separated marshes developed c ad 1200 and 1350 after the known period of human colonisation and establishment detailed analyses pollen sediments and charcoal and additional dating of the upland core from t vi i plateau 810 m allow for identification of four chronozones the core sediment data and age depth curve suggest an alternation of wet dry wet conditions over the c 750 year period the pollen spectra in contrast are fairly stable with ferns dominating but arborescent species also present the micro charcoal evidence points to regional burning and long distance transport until c ad 1640 after which localised burning may be indicated among the more notable changes is a major increase in pollen and spore deposition after c ad 1640 a trend most evident in the pollen concentration diagram overall the data suggest rapid sedimentation in the fourteenth century ad followed by drier and or more settled conditions until the mid seventeenth century and finally wetter conditions after c ad 1640 the latter in particular is consistent with emerging regional evidence for warm wet conditions in the central eastern pacific during the seventeenth century the height of the northern hemisphere little ice age the charcoal record also provides insights into human activities on the island suggesting burning in the lowlands from the fourteenth century ad probably in conjunction with forest clearance preparatory to tree and root crop cultivation

continental rift to back arc basin jurassic cretaceous stratigraphical and structural evolution of the larsen basin antarctic peninsula the larsen basin developed in jurassic times as a result of continental rifting during the early stages of gondwana break up lower upper jurassic non marine sedimentary and volcanic rocks constitute a syn rift megasequence recording initial largely amagmatic extension and subsequent widespread extension related silicic volcanism a succeeding kimmeridgian early berriasian transgressive megasequence consisting largely of anoxic dysoxic hemipelagic mudstones is thought to have been deposited during a thermal subsidence phase when relative magmatic quiescence and peak jurassic eustatic sea levels served to maximize sediment starvation the fragmentary record for late berriasian barremian times suggests that a regressive megasequence may have developed in the earlier part of this period recording increased sediment yield to the larsen basin from the increasingly emergent antarctic peninsula arc subsequently strata in the southern but not the northern part of the basin underwent relatively intense eastward verging deformation possibly during the formation of a retro arc fold thrust belt where exposed the lower part of the succeeding aptian eocene megasequence consists of a deep marine clastic wedge deposited along the fault bounded western basin margin during a phase of arc uplift and related differential subsidence following partial basin inversion in late cretaceous times regression took place as reduced basinal subsidence rates allowed shallow marine facies to prograde basinward

northern and southern hemispheres ostracod palaeobiogeography during the early jurassic possible migration routes abstract the purpose of this paper is to review the palaeobiogeographical distribution of early jurassic ostracod species worldwide to establishing possible migration pathways between the north and south hemispheres in direction and timing and in particular to examine the existence of a seaway through central america the hispanic corridor from at least the pliensbachian toarcian a detailed taxonomic revision of over 270 early jurassic ostracod species from europe north africa south america asia and australia a revision of every figured specimen and or taxon included in each list of synonymous taxa has been undertaken each assemblage was subjected to a quantitative analysis this metric was calculated using the dice similarity index in order to ascertain the degree of similarity between ostracod assemblages from both hemispheres the obtained results indicate that there is a clear differentiation between australian and argentinean ostracod assemblages in relation to european ostracod assemblages the australian faunas are similar to western tethyan and central european assemblages probably indicating a communication route along the western tethys aided by the action of western currents moreover the argentinian ostracod assemblages exhibit a high degree of similarity with north western european portugal grand banks the fasnet basin and wales and north african assemblages through the detailed analysis of ostracod spatial and temporal distribution the coeval occurrence of taxa in argentina and western europe and the differences between australian and argentinian faunas and the pattern of ocean currents derived from climate models simulations it would infer the existence of the hispanic corridor

the provenance of low calcic black shales the elemental concentration of sedimentary rocks depends on the varying reactivity of each element as it goes from the source through weathering deposition diagenesis lithification and even low rank metamorphism however non reactive components of detrital particles ideally are characteristic of the original igneous source and thus are useful in provenance studies to determine the source of detrital granitic and volcanic components of low calcic 1 caco3 marine black shales the concentrations of apparently non reactive i e unaffected by diagenetic redox and or low rank metamorphic processes trace elements were examined using standard trace element discrimination diagrams developed for igneous rocks the chemical data was obtained by neutron activation analyses of about 200 stratigraphically well documented black shale samples from the cambrian through the jurassic a la th sc ternary diagram distinguishes among contributions from the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 all the low calcic black shales cluster within the region of the upper crust th hf co ternary diagrams also are commonly used to distinguish among the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 as co is redox sensitive in black shale environments it was necessary to substitute an immobile element i e example rb in the diagram with this substitution of black shales all cluster in the region of the upper continental crust to determine the provenance of the granitic component pearce et al 1984 plots of ta vs yb and rb vs yb ta shows a cluster at the junction of the boundaries separating the volcanic arc granite vag syn collision granite syn colg and within plate granite wpg fields the majority fall within the vag field there are no occurrences of ocean ridge granite org the minimal contribution of basalts to marine black shales is confirmed by the ternary wood diagram th hf 3 ta wood et al 1979 the black shales plot in a cluster in a high th region outside the various basalt fields which suggests contribution from the continental crust

redating the onset of burning at lynch s crater north queensland implications for human settlement in australia lynch s crater preserves a continuous high resolution record of environmental changes in north queensland this record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries this increase is accompanied or closely followed by the virtually complete replacement of rainforest by sclerophyll vegetation the absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area the age for this increase in burning on the basis of conventional radiocarbon dating was previously thought to be approximately 38000 c 14 yr bp supporting the traditional model for human arrival in australia at 40 000 c 14 yr bp here we have applied a more rigorous pre treatment and graphitisation procedure for radiocarbon dating samples from the lynch s crater sequence these new dates suggest that the increase in fire frequency occurred at 45 000 c 14 yr bp supporting the alternative view that human occupation of australia occurred by at least 45 000 55 000 cal yr bp copyright c 2001 john wiley sons ltd

late jurassic to early cretaceous black shale formation and paleoenvironment in high northern latitudes examples from the norwegian greenland seaway 1 the late jurassic to early cretaceous volgian ryazanian was a period of a second order sea level low stand and it provided excellent conditions for the formation of shallow marine black shales in the norwegiangreenland seaway ngs iku petroleum research drilling cores taken offshore along the norwegian shelf were investigated with geochemical and microscopic approaches to 1 determine the composition of the organic matter 2 characterize the depositional environments and 3 discuss the mechanisms which may have controlled production accumulation and preservation of the organic matter the black shale sequences show a wide range of organic carbon contents 0 5 7 0 wt and consist of thermally immature organic matter of type ii to ii iii kerogen rock eval pyrolysis revealed fair to very good petroleum source rock potential suggesting a deposition in restricted shallow marine basins well developed lamination and the formation of autochthonous pyrite framboids further indicate suboxic to anoxic bottom water conditions in combination with very low sedimentation rates it seems likely that preservation was the principal control on organic matter accumulation however a decrease of organic carbon preservation and an increase of refractory organic matter from the volgian to the hauterivian are superimposed on short term variations probably reflecting milankovitch cycles various parameters indicate that black shale formation in the ngs was gradually terminated by increased oxidative conditions in the course of a sea level rise index terms 1055 geochemistry organic geochemistry 4802 oceanography biological and chemical anoxic environments 9609 information related to geologic time mesozoic 8105 tectonophysics continental margins and sedimentary basins 1212 keywords black shale formation depositional environment norwegian greenland seaway mesozoic organic petrography citation langrock u r stein m lipinski and h j brumsack late jurassic to early cretaceous black shale formation and paleoenvironment in high northern latitudes examples from the norwegian greenland seaway paleoceanography 18 3 1074 doi 10 1029 2002pa000867 2003

lightning induced mineral chemical changes in red pine pinus resinosa abstract red pine pinus resinosa growing in sandy soil of glacial lake whittlesey age 13 12 ka in the town of waterford ontario canada north of lake erie was struck by lightning in a fierce thunderstorm may 2010 the lightning strike was strong enough to destroy television sets and telephones in nearby houses and two red pines were struck one split down the middle from above the bole to near the crown samples of bark and inner tissue were examined to determine the composition of black silt size specs seen on the severed material in addition to minerals found in abundance in the local soil c clots spherules disrupted cellulose structures blackened tissue fused disfigured si and metallic sheets of na the latter sourced from melted albite na rich plagioclase were analyzed many silt and sand size particles sourced from the local soil were presumably electrically levitated along and within the bark by the lightning discharge iron rich micas other fe minerals and a great range of light minerals moistened by torrential rain were among the silts and sands transported to great height and embedded in the bark

genetic diversity of manganese deposition in the terrestrial geological record terrestrial manganese deposits formed by hydrothermal sedimentary and supergene processes ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction related settings and those deposited from terrestrial hot springs are discussed sedimentary mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea level changes mn carbonate deposits probably formed by diagenesis through mn oxyhydroxide reduction coupled with organic matter oxidation climatic variation and basin water stratification responsible for mn concentration were manifestations of atmospheric coz content prompted by tectonism supergene manganese enrichment in continental weathering profiles was mainly dictated by climate topography and drainage systems manganese deposits of diverse genetic types occur in the terrestrial geological record roy 1981 these were produced by direct hydro thermal activity sedimentary processes and continental weathering although the processes may be interrelated each involves distinct mechanisms that place the deposits into specific genetic types some of these processes are best understood in preset day depositional sites the ancient environments were determined by the intensity and style of tectonism volcanism and hydrothermal activity the composition of the atmosphere and the hydrosphere and the development of the biosphere which all varied with time it is my intention to unfold the total panorama of the environmental evolution during different time envelopes that produced a variety of manganese deposits in the past only major deposits and those providing distinctive evidence of their environment of deposition will be considered here

phosphate authigenesis in the aramachay formation lower jurassic of peru abstract the aramachay formation lower jurassic of the peruvian central cordillera is made up of 300 m of organic rich mudstones ichpachi member which grade up into 100 m of phosphatic siltstones chart and arenites alata member the organic rich mudstones are slightly enriched in p2o5 0 5 p2o5 but do not contain visible authigenic phosphate the organic maturity of the rocks as evidenced from kerogen elemental analysis may serve to explain this radiolaria in this facies are generally calcitized in contrast radiolaria in the phosphatic siltstones are phosphatized occurring within apparently authigenic blabs and stringers of collophane 2 p2o5 whole rock in addition this facies although with a lower organic ca bon content contains the remains of sponges benthic blue green algae and a few epibenthic bivalves monospecific it also contains more silt and some glauconite it is inferred that the site of phosphate authigenesis lay wholly within this phosphatic siltstone facies which records low or fluctuating oxygenation rather than fully anoxic conditions this hypothesis is supported by studies of other similar sequences and by published carbon and sulfur isotope data it is proposed that the facies sequence represents the fossilized upper margin of an oceanic o2 minimum zone comparable with that observed on the modern peruvian shelf such an environment has been suggested for phosphate authigenesis before but has not previously been identified in the stratigraphic record the f ne grained sequence is sharply overlain by phosphatic lithoclastic arenites 8 p2o5 whole rock in which the rounded phosphate grains contain radiolaria and are therefore inferred to have been eroded from the underlying siltstone these are in turn overlain by shallow marine carbonates completing a sequence interpreted to represent a substantial marine regression

a revised sea level curve for the early jurassic a comparison is undertaken of three different methods of eustatic sea level analysis 1 shallowing and deepening transgressive events inferred from the facies sequence 2 changes through time in the areal spread of epicontinental seas 3 seismic stratigraphy the results of these methods are compared mainly with reference to the lower jurassic new data are brought forward from several continents in a stage by stage study and it is concluded that thelias was characterized by interrupted sea level rise with no major regressions both the transgressions and regressions were relatively rapid with the major transgressions associated with widespread anoxic bottom waters estimates of the net amount of sea level rise through early jurassic time range from 75 m to 110 m

late mesozoic sedimentation in the northern antarctic peninsula and its relationship to the southern andes two distinct phases of island are evolution are recognized in late mesozoic sedimentary rocks of the northern antarctic peninsula during late jurassic kimmeridgian tithonian times alternating radiolaria rich mudstones and ash fall tuffs were deposited under shallow marine euxinic conditions in association with restricted volcanic centres the name nordenskjold formation is proposed for this lithostratigraphic unit subsequently during the early cretaceous a major episode of volcanism and uplift led to the construction of an emergent are terrane simultaneous development of a retro arc basin resulted in the accumulation of coarse volcaniclastic detritus along the eastern side of the arc retro are sedimentation and intermittent volcanism continued into the late cretaceous and early tertiary although the pattern of sedimentation in the northern antarctic peninsula is broadly comparable to that of the southern andes an active marginal basin has not been recognized in the former area interbedded mudstones and tuffs identical to those of the nordenskjold formation were deposited in the southern andes and south georgia during the late jurassic early cretaceous

rapid deforestation of south island new zealand by early polynesian fires in most parts of the world where people have colonized and modified their landscapes for several millennia or more it is often difficult to discriminate anthropogenic burning from natural fire regimes that are linked to climate regimes new zealand provides a unique setting for identifying human influence on fire occurrence because it was settled recently c ad 1280 at a time when climates are considered to be similar to today late holocene pollen and charcoal records from new zealand provide striking evidence for initial polynesian m ori arrival being strongly associated with widespread burning and loss of native forest the duration of initial forest clearance and the spatial pattern of burning that led to this transformation are still poorly understood we present high resolution charcoal and pollen analyses of sediment cores from five lakes located on the deforested eastern side of the southern alps these records document the local fire history of the last 1000 years and the response of vegeta

phytoplankton evidence for the timing and correlation of palaeoceanographical changes during the early toarcian oceanic anoxic event early jurassic the causes and duration of the early toarcian anoxic event are controversial integration of data from calcareous and organic phytoplankton provides a biochronological framework that allows precise correlations across the western tethys in particular the carinolithus superbus nannofossil zone can be used to correlate the levels enriched in organic matter and the related 13 c negative excursion although a variable duration is given in the literature for this negative excursion it is likely that it lasted between 520 and 650 ka increased atmospheric p co 2 related to excess volcanic emissions magmatic activity in the karoo and ferrar provinces had an impact on climate and ocean chemistry and marked the inception of a biotic crisis affecting many organisms the beginning of the crisis within shallow carbonate platforms documented at southern latitudes predates the levels enriched in organic matter dinoflagellate cysts experienced a decrease in abundance in the c superbus zone until they temporarily disappeared the nannoplankton crisis was twofold a decrease in size and low calcified specimens are observed in addition to a drastic decrease in absolute abundance the increased atmospheric p co 2 as a result of the magmatic activity and temporarily amplified by transient methane release could have been the trigger for the biocalcification crisis which first affected the probably more reactive neritic system and eventually the nannoplankton community

depositional conditions and organic matter preservation pathways in an epicontinental environment the upper jurassic kashpir oil shales volga basin russia abstract the middle volgian kashpir oil shales formation located on the russian platform is a lateral equivalent of the north sea and west siberian petroleum source rocks in the volga basin this formation is 6 m thick and shows alternations of marls and black shales the organic carbon content is often higher than 1 although bioturbation and benthos are abundant even in the black shales in the marls highly degraded organic matter om dominates while aliphatic sulphur rich om is dominant in the black shales the combination of sedimentological and geochemical studies allowed to determine that the redox conditions of the sediment regularly fluctuated from oxic to anoxic under relatively productive waters while climatic conditions were increasingly arid it is proposed that om deposition occurred in relation to the increasing aridity through the combination of recurrent disruption of salinity stratification and aeolian supply of iron which both promoted phytoplankton productivity

experiments on internal strain in lava dome cross sections simple experiments have been conducted to study the strain evolution in lava dome cross sections a viscous fluid is injected vertically from a reservoir into a feeding conduit silicone putty is used as analogue magma two dimensional experiments allow the assessment of the internal strain within the dome particle paths are symmetrical on either side of a central line passing through the feeding conduit and display parabolic trajectories the highest strain zone is located above the extrusion zone in cross sections stretch trajectories show a remarkable concentric pattern wrapping around the extrusion zone of the analogue magma to the lateral margins a triple junction of stretch trajectories defines an isotropic point in the strain field in the main central part of the dome an intermediate zone of reversed sense of shearing is caused by a change in the sign of the velocity gradient with respect to that in the upper and lower zones knowledge of this evolving strain pattern can provide a better understanding of the evolution of natural domes also it can help to unravel the kinematic history of ancient domes partly removed by erosion

the mantled gneiss domes of kuopio finland interfering diapirs abstract finite strain data from the kuopio mantled gneiss domes are described synclines located between two domes have flattening type strains while those situated between more than two domes exhibit constrictional strains cleavage trajectory patterns show that cleavage tends to parallel the dome boundaries and encloses characteristic points termed cleavage triple points at junctions of synclines the stretching lineation is generally steeply plunging in a mean southwest direction folds range from inclined to reclined their asymmetry is apparently related to irregularities in the cover basement boundary two shear components of the deformation have been deduced from available data the major one is steeply plunging and is well exhibited by cleavage fans steeply plunging lineations and finite strain gradients the second shear component is horizontal as deduced from asymmetric folds and other small scale structures and is controlled by bosses and dimples in the cover basement boundaries the described structural features are explained in terms of interference between progressively inflating neighbouring diapirs furthermore some of these features such as cleavage triple points flattening between two domes and constriction between three or more domes and horizontal shear components controlled by cover basement boundary irregularities could be used as criteria of diapirism a model of progressive dome interference is presented in which each dome inflates and interacts with neighbours such a model could possibly be applied to other orogenic situations with closely spaced diapirs e g archean greenstone belts or granite rich orogenic belts

vertical variations of organic matter content in guayuta group upper cretaceous interior mountain belt eastern venezuela abstract a geochemical study of the vertical variations of organic matter in the guayuta group querecual and san antonio formations has been conducted on a series of samples taken from a sedimentary sequence outcropping in the interior mountain belt the results indicate that despite very high thermal maturity the organic matter content in the samples is still very high and shows geochemical characteristics related to anoxic paleoenvironmental conditions of sedimentation based on micropaleontological data mineralogical data and trace metal v ni ratio of kerogen the analysis of the sequence shows stronger anoxic depositional conditions toward the base of the section and an increase of clastic sediments toward the top the total organic carbon of the sediments increases toward the base of the sequence in addition there are pseudocyclic patterns and heterogeneities of the organic carbon content distribution at the meter scale the results indicate that the lower part of this sedimentary sequence represents a major anoxic event that can be correlated with other sequences of middle and upper cretaceous age

holocene palaeofire records in a high level proximal valley fill wilson bog mount lofty ranges south australia an elevated valley fill peat bog wilson bog near mount lofty south australia failed in november 2005 following a flooding event and exposed representative sections of the sediment infill two

seawater redox variations during the deposition of the kimmeridge clay formation united kingdom upper jurassic evidence from molybdenum isotopes and trace metal ratios 1 the kimmeridge clay formation kcf and its equivalents worldwide represent one of the most prolonged periods of organic carbon accumulation of the mesozoic in this study we use the molybdenum mo stable isotope system in conjunction with a range of trace metal paleoredox proxies to assess how seawater redox varied both locally and globally during the deposition of the kcf facies with lower organic carbon contents toc 1 7 wt were deposited under mildly reducing suboxic conditions while organic rich facies toc 7 wt accumulated under more strongly reducing anoxic or euxinic local conditions trace metal abundances are closely linked to toc content suggesting that the intensity of reducing conditions varied repeatedly during the deposition of the kcf and may have been related to orbitally controlled climate changes long term variations in 98 95mo are associated with the formation of organic rich intervals and are related to third order fluctuations in relative sea level differences in the mean 98 95mo composition of the organic rich intervals suggest that the global distribution of reducing conditions was more extensive during the deposition of the pectinatites wheatleyensis and lower pectinatites hudlestoni zones than during the deposition of the upper pectinatites hudlestoni and pectinatites pectinatus zones the global extent of reducing conditions during the kimmerigidan was greater than today but was less widespread than during the toarcian early jurassic oceanic anoxic event this study also demonstrates that the mo isotope system in jurassic seawater responded to changes in redox conditions in a manner consistent with its behavior in present day sedimentary environments

depositional conditions of the bathonian to hauterivian janusfjellet subgroup spitsbergen abstract the janusfjellet subgroup was formed under shallow marine shelf conditions dominated by sedimentation of clay but silt and sand also accumulated in significant amounts the sand bodies recognized in the agardhfjellet formation bathonian b are redeposition of sediments originating from earlier deltaic coastal progradation the rurikfjellet formation berriasian hauterivian reveals an upwards increasing sand content reflecting built out of a delta system the prodeltaic material was partly reworked by storm currents the shales of the agardhfjellet formation were in part deposited under oxygen depleted conditions

glacial interglacial control of terrigenous and biogenic fluxes in the deep ocean off a high input collisional margin a 139 kyr record from new zealand abstract sediment input to the deep ocean off the new zealand collisional plate boundary is large and variable as revealed by a 139 kyr old record from the 34 92 m long core md97 2121 mass accumulation rates mars were derived for terrigenous and biogenic carbonate and silica sedimentary components with temporal control from a stable isotope age model verified by tephra and radiocarbon ages terrigenous mars changed in phase with glacio eustatic fluctuations of sea level highest rates 30 g cm 2 kyr coincided with the late regressive lowstand early transgressive phase of marine isotope stage mis 2 when rivers discharged at or near the shelf edge lesser but still high terrigenous rates 20 30 g cm 2 kyr characterized peak warm phases of early mis 5 and 1 when a strengthened subtropical inflow probably introduced sediment from fluvial and seabed sources to the north of md97 2121 however during prolonged highstands the flux declined as more sediment was retained on a tectonically subsiding shelf with a shore parallel current paradoxically the lowest mars 10 5 g cm 2 kyr occurred in mis 4 either sea level was too high to allow much sediment to escape off shelf or the fluvial input was modest or both these factors despite the terrigenous dominance biogenic mars are high and are 2 4 times larger than sw pacific ocean rates mars were lowest during mis 4 and 3 possibly due to reduced marine production under a lowered input of fluvial micronutrients in contrast mars increased irregularly though glacial maxima to peak at 5 6 g cm 2 kyr carbonate and 2 2 5 g cm 2 kyr silica in early mid mis 5 and 1 such rates reflected the interaction of macronutrient rich subantarctic waters sourced from the south with local micronutrient rich subtropical waters production also responded to warmer temperatures elevated nutrient runoff and a more stratified surface ocean later in mis 5 and 1 fluxes reduced as less productive subtropical waters prevailed that biogenic and aeolian mar profiles are out of phase suggests fe fertilization by aerosolic dust was not a major influence

strain patterns in an ice cap and implications for strain variations in shear zones glacier flow is a form of gravity tectonics in thin sheets characterized by the development of large strains foliation and folds strain is difficult to measure in ice but numerical methods provide a good means of estimating cumulative strains in simple terms flow in an ice cap involves vertical flattening at the center with bottom parallel shear increasing in intensity downwards and outwards in steady state cumulative strains will be plane if flow is two dimensional as in parts of many valley glaciers and some ice caps and of flattening type if lateral extension occurs normal to the flow direction as in many ice sheets in both radial and plane flow strain gradients will be large vertically and low horizontally outwards cumulative strain magnitude can be extremely large near the base and at the margin z is everywhere sub vertical if flow is unsteady more complex strain patterns develop even if changes in the flow field are slight over bedrock ridges flow perturbations can lead locally to rotations greater than those of the quasi simple shear acting near the base in steady state flow this may cause the x direction of the cumulative strain to rotate through the shear plane in the neighborhood of the perturbation in which case strain magnitudes subsequently diminish leading to low or zero strains in plane flow and to constrictional strains in radial flow in the latter case x lies horizontal and perpendicular to the flow direction and we have local constrictional strain in an overall flattening field the zones of perturbed strain tend to be associated with the inverted limbs of recumbent folds shear zones in rocks are expected to show similar patterns of strain perturbation

sedimentary manganese metallogenesis in response to the evolution of the earth system abstract the concentration of manganese in solution and its precipitation in inorganic systems are primarily redox controlled guided by several earth processes most of which were tectonically induced the early archean atmosphere hydrosphere system was extremely o2 deficient thus the very high mantle heat flux producing superplumes severe outgassing and high temperature hydrothermal activity introduced substantial mn2 in anoxic oceans but prevented its precipitation during the late archean centered at ca 2 75 ga the introduction of photosystem ii and decrease of the oxygen sinks led to a limited buildup of surface o2 content locally initiating modest deposition of manganese in shallow basin margin oxygenated niches e g deposits in india and brazil rapid burial of organic matter decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the archean proterozoic transition concurrently a massive drawdown of atmospheric co2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused paleoproterozoic glaciations 2 45 2 22 ga the spectacular sedimentary manganese deposits at ca 2 4 ga of transvaal supergroup south africa were formed by oxidation of hydrothermally derived mn2 transferred from a stratified ocean to the continental shelf by transgression episodes of increased burial rate of organic matter during ca 2 4 and 2 06 ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere black shale hosted mn carbonate deposits in the birimian sequence ca 2 3 2 0 ga west africa its equivalents in south america and those in the francevillian sequence ca 2 2 2 1 ga gabon are correlatable to this period tectonically forced doming up attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric co2 drawdown causing glaciation on the neoproterozoic rodinia supercontinent tectonic rifting and mantle outgassing led to deglaciation dissolved mn2 and fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation during the sturtian glacial interglacial event ca 750 700 ma interstratified mn oxide and bif deposits of damara sequence namibia was formed the varangian marinoan ca 600 ma cryogenic event produced mn oxide and bif deposits at urucum jacadigo group brazil the datangpo interglacial sequence south china liantuo nantuo varangian event contains black shale hosted mn carbonate deposits the early paleozoic witnessed several glacioeustatic sea level changes producing small mn carbonate deposits of tiantaishan early cambrian and taojiang mid ordovician in black shale sequences china and the major mn oxide carbonate deposits of karadzhal type central kazakhstan late devonian the mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans during the early jurassic oae organic rich sediments host many mn carbonate deposits in europe e g urkut hungary in black shale sequences the late jurassic giant mn carbonate deposit at molango mexico was also genetically related to sea level change mn carbonates were always derived from mn oxyhydroxides during early diagenesis large mn oxide deposits of cretaceous age at groote eylandt australia and imini tasdremt morocco were also formed during transgression regression in greenhouse climate the early oligocene giant mn oxide carbonate deposit of chiatura georgia and nikopol ukraine were developed in a similar situation thereafter manganese sedimentation was entirely shifted to the deep seafloor and since ca 15 ma b p was climatically controlled glaciation deglaciation assisted by oxygenated polar bottom currents aabw nadw the changes in climate and the sea level were mainly tectonically forced

particle size evidence for source areas of charcoal accumulation in late holocene sediments of eastern north american lakes abstract two methods of analyzing charcoal in sediment reveal changes in charcoal accumulation across temperate eastern north america during the last several hundred years in one method the analyst counts mostly small particles that reflect regional emissions in the other the analyst counts only larger particles derived mostly from such local sources as catchment fires we used these methods to compare charcoal accumulation at 14 lakes from the prairie forest border in minnesota to eastern maine the two methods gave concordant accumulation rates for sediments of pre 1850 age at each of 4 lakes analyzed by both methods this concordance is consistent with the interpretation that pre 1850 emissions were controlled by broad scale factors such as climatically controlled regional differences in fuels and moisture since 1900 large particles decreased greatly and small particles decreased slightly in minnesota and wisconsin by contrast in the northeast the large particle accumulation has remained at the low values measured in pre 1900 sediments at most sites while small particles increased everywhere east of central new york and pennsylvania the observed patterns suggest that 1 large particles primarily reflect local fires that were common in the midwest before fire suppression became effective 2 large particles were rare in the northeast especially before extensive land clearance 3 small particles reflect regional combustion that increased in the northeast after extensive use of fire for land clearance and wood burning for industrial purposes of the 19th century and 4 small particles remain abundant in the midwest long after effective fire suppression probably because these well dispersed small particles have a large source area that extends beyond the local wildfires that account for large particles before european settlement

the jurassic succession in west central argentina stratal patterns sequences and paleogeographic evolution abstract jurassic rocks in west central argentina are predominantly marine and marginal marine siliciclastics associated with prominent but volumetrically subordinate carbonates and evaporites facies developments were ruled by paleogeographic persistence within the southern infratropical latitude belt within 40 50 s and by siliciclastic derivation from the patagonian hinterland to the southwest minor volcanic and volcaniclastic supply arrived from the west out of a magmatic belt related to circum pacific convergence timing of the main marine flooding events and general correspondence with the high rank stratal packaging recorded in western north america suggest that global eustasy was also a factor in controlling the local stratigraphic record early jurassic sedimentation occurred within a series of semi isolated depocentres linked to fault bounded triassic troughs the sinemurian toarcian deposits record depocentre expansion and coalescence these trends were coeval with progressively more widespread marine invasions from the northwest and west leading to an elongate marine seaway which connected central patagonia with the pacific domain during the aalenian bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment bathonian and early callovian were times when coarse clastics prograded into the basin while the marine embayment shrank as a result of stepwise forced regressions during late callovian to oxfordian globally rising sea level the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance that promoted cratonward onlap and inception of widespread carbonate deposition ooidal coralline carbonate development was terminated after a relatively sudden messinian style event that desiccated a large tract of the andean basin and favored massive precipitation of anhydrite in the course of the kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat salina complex linked to a widespread erg and to an ephemeral drainage system by the tithonian at a period of peak oceanic stand marine connection was reinstated and recorded as the most widespread jurassic transgression across the neuquen aconcagua embayment shelfal deposition consisted of molluscs and ooid dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations like in other prolific petroleum provinces around the world the tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content

interpreting charcoal in new zealand s palaeoenvironment what do those charcoal fragments really tell us the role of charcoal as a palaeoenvironmental indicator has never been fully or adequately explained charcoal fragments are often interpreted as evidence for natural fires caused by lightning strike during drought or dry climatic conditions generally no evidence is presented to show this to be the case the frequency of lightning strike in new zealand is not high and the extent to which it is a causal factor in generating forest fire is questioned the assumption is often made that charcoal fragments found in sedimentary deposits are local or at least reasonably local in origin this assumption is being challenged fine charcoal fragments appear to be transported regionally within new zealand it is highly likely that fine charcoal fragments are being transported from australia both by thermal convection during fires and during dust storm events to be deposited into new zealand sediments the consequences of this in interpreting new zealand s palaeo history requires researchers to at the very least provide charcoal counts within size parameters this is particularly so for archaeologists who would definitely need to show the presence of large charcoal fragments before interpreting the possibility of people in the landscape

magmatic strains and foliation triple points of the merrimac plutons northern sierra nevada california implications for pluton emplacement and timing of subduction abstract cross cutting relationships between regional structures and post tectonic plutons of known age are commonly used to date regional deformation in orogenic belts in order to show that a pluton is post tectonic one must demonstrate that the strains within the pluton are not due to regional tectonic processes this paper reports strain measurements associated with pluton emplacement in northern sierra nevada these strain data and a microstructural analysis indicate that strains within the merrimac plutons are due to igneous not tectonic processes which strengthens the hypothesis that the plutons were emplaced after the formation of regional structures and melanges radiometric ages of the merrimac pluton in concert with structural data place a more reliable upper jurassic limit on the age of the subduction in the western belt of northern sierra nevada this paper also reports constrictional strains around plutons and suggests that the merrimac plutons contributed significantly to the ductile strains observed in the wall rocks

cretaceous marine nutrients greenhouse carbonates and the abundance of turritelline gastropods abstract modern marine carbonate sediments accumulate where carbonate producing organisms are abundant and siliciclastic input is low such accumulations occur today in two main environments and may be characterized as warm low nutrient wln also known as tropical or chlorozoan carbonates or cool high nutrient chn also known as cool water temperate nontropical foramol or heterozoan carbonates few carbonates form today in warm high nutrient whn conditions because such environments are very rare modern wln environments occur mainly in low latitudes where nutrients from upwelling or terrestrial runoff are low modern chn environments occur mainly in middle to high latitudes where nutrients mostly from upwelling are abundant however whn depositional environments may have been widespread during the cretaceous and paleogene during these times upwelled nutrient rich waters would in general have been warmer than they are today nutrients in these waters supported diverse carbonate produc

terrestrial palynology from marine cores as an indicator of environmental change for the waipaoa sedimentary system and north eastern new zealand diverse terrestrial palynomorph assemblages of pleistocene to recent age have been recovered from mainly marine sediment cores along the eastern new zealand margin these assemblages record a range of environmental changes including climate deforestation reforestation rates of erosion sediment provenance and age volcanic activity polynesian and european settlement strength and direction of ocean currents astronomical cyclicity and other major events many of which can be correlated with shorter onshore terrestrial sequences as such pollen yields valuable information on the dynamic new zealand landscape which is of particular relevance to a source to sink approach this paper provides an integrated summary of published and unpublished late pleistocene palynological studies off eastern north island new zealand that gives context for an analysis of cores within and marginal to the waipaoa sedimentary system pollen assemblages faithfully reflect the last glacial vegetation dominated by grass and shrub land species together with elevated tertiary pollen from enhanced erosion of the regolith the glacial termination and holocene were marked by establishment of podocarp forest a mid holocene disappearance of sediment trapping mangroves and introduction of distal pollen with establishment of coastal current systems under rising sea level these natural signals are overprinted by abrupt changes in pollen species caused by volcanic eruptions finally endemic forest and shrub pollen were markedly reduced with human colonisation associated land use changes and introduction of exotic species

stratigraphy chronology styles and dynamics of late quaternary eruptions from taupo volcano new zealand taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite dominated central portion of the taupo volcanic zone in the north island of new zealand taupo has an average magma output rate of 0 2 m 3 s 1 over the past 65 000 years and is one of the most frequently active and productive rhyolite volcanoes known the structure of the modern inverse volcano was formed largely by caldera collapse associated with the voluminous 22 600 14 c years bp oruanui eruption and has been little modified since except for collapse following the 1850 14 c years bp eruption the products of 28 eruptions labelled psi omega a ldots z all of which post date the oruanui eruption are defined and described here twenty seven of these eruptions are represented by pyroclastic deposits of which three were accompanied by a mappable lava extrusion and one eruption z solely by evidence for a lava extrusion the deposits of seven eruptions b c e s v x and y largely correspond to previously defined tephra formations karapiti poronui opepe waimihia whakaipo mapara and taupo respectively the previously defined motutere and hinemaiaia tephras are reinterpreted to represent the products of 12 eruptions g to r while the remaining eight deposits and one eruption are newly recognized eruption psi occurred at ca 17 200 14 c or 20 500 calibrated years bp and eruption z about 1740 calibrated years bp eruption volumes vary by more than three orders of magnitude between 0 01 and more than 44 km 3 and repose periods by more than two orders of magnitude from ca 20 to 6000 years the eruption deposits reflect great variations in parameters such as volume the dispersal characteristics of the fall deposits the presence or absence of intraeruptive time breaks the formation of pyroclastic flows the degree of magma water interaction the vesiculation state of the magma on fragmentation and the relative proportions of juvenile obsidian versus foreign lithologies in the lithic fractions all but seven fall deposits are plinian in dispersal two y1 and probably w are sub plinian one y5 has been termed ultraplinian while psi and a are too poorly preserved for their dispersal to be assessed the lengths of repose periods in the post oruanui sequence range are not randomly distributed but show self similar properties fractal dimensionality repose intervals r in years of not more than 350 years follow n 53 5r 0 21 and those of not less than 350 years follow n 2096r 0 83 where n is the number of eruptions the shorter repose periods may reflect triggering processes such as regional extension affecting magma bodies during their viable lifetimes while longer repose intervals i e not less than 350 years may reflect an episodicity of major rifting events or the production of magma bodies below the volcano bulk volumes v in km 3 of the eruption products also show self similar properties fractal dimensionality with n 6 17v 0 46 however there are then apparently random relationships between eruption volumes and the preceding or succeeding repose period such that prediction of the time and size of the next eruption is impossible the post oruanui activity at taupo represents noise superimposed on the more uniform longer term activity in the central taupo volcanic zone where large greater than 100 km 3 eruptions such as the oruanui occur at more evenly spaced intervals of one per 40 60 000 years

isotropic points and lines in strain fields abstract in heterogeneous strain fields the strain may be isotropic at some points or along some lines called isotropic points and isotropic lines these isotropic features are known in various strain environments such as folds diapirs nappes or shear zones mechanical instabilities involving flow cells diapirism and folding are able to produce simultaneously isotropic points and lines whose dimensions location and migration are controlled by the flow pattern and history many other isotropic points can be understood in terms of superposition of elementary flows some examples such as neighbouring diapirs synkinematic diapirs shear zone terminations and spreading sliding nappes are presented finally some three dimensional aspects and general properties of isotropic points and lines are discussed

anisotropy of magnetic susceptibility as a strain gauge in the flamanville granite nw france the relationship between strain and anisotropy of magnetic susceptibility ams has been investigated in the carboniferous flamanville granite in the armorican massif nw france we measured the axial ratios of elliptical inclusions and the orientation of cleavage planes at eight sites around the granite margin measurements of ams were made on 73 specimens using a schonstedt spinner magnetometer ams measurements are shown to provide accurate predictions of cleavage and lineation direction even where these structures are difficult to measure in the field the strain and ams ellipsoids show similar regional variations in shape and intensity and a good correlation between the lengths of the principal axes finally our data are consistent with the hypothesis that the flamanville granite was syntectonically emplaced during the late stages of the hercynian orogeny

strain localisation in an orthogneiss laccolith the pinet massif aveyron southern france abstract sheared granitoids of the pinet laccolith southern france display strain gradients from undeformed protolith to s c mylonites and ultramylonites that formed at amphibolite facies of metamorphism we study shear strain distribution at a regional scale and use image processing techniques to measure strain across continuous shear gradients local perturbations of strain intensity seem to represent early stages of shear strain localisation parallel to the main mylonitic foliation our study suggests that localisation of shear strain shows a periodicity at regional and outcrop scales

the influence of sea level and tectonics on late pleistocene through holocene sediment storage along the high sediment supply waipaoa continental shelf abstract we present geophysical and core evidence showing how subsidence caused by forearc shortening has accommodated late pleistocene and holocene sediments supplied to the tectonically active waipaoa shelf nz limiting off shelf export during the early sea level highstand the last glacioeustatic fall and subsequent rise exposed and then flooded a shelf segmented into subbasins separated by zones of uplift leaving key stratigraphic markers of shoreline regression and transgression that vary strongly in character across the shelf highstand sediment isopachs tied to piston cores dated using tephra correlation and a radiocarbon age model provide a sediment budget at 2000 yr intervals from the mid holocene 5500 cal yr bp to present sediment load estimates from our shelf budget are in agreement with published model estimates for suspended sediment discharge from the waipaoa river for the past 3000 yr but importantly do not show the 6 fold increase in the waipaoa s sediment output that began with human settlement 700 yr ago and accelerated with deforestation over the last century bypassing of waipaoa sediment to the slope may therefore be a recent phenomenon caused by unnaturally high sediment loads a conclusion supported by data reported elsewhere in this volume our study also reveals evidence for 1 a relatively thick mid shelf transgressive section deposited during the last eustatic rise that may correlate to estuarine sequences reported from numerous sites on the modern coastline of the north island 2 a slight decrease in total basin filling rates during the highstand and 3 variability in the partitioning of highstand sediments between individual subbasins that may reflect differing degrees of tectonic accommodation

low temperature deformation mechanisms at a lithotectonic interface near the sudbury basin eastern penokean orogen canada abstract southwest of the sudbury basin variations in macroscopic strain microstructure and deformation mechanisms within archaean granitoid basement and overlying proterozoic rocks suggest that rock strength was strongly influenced by large amounts of fluids ductilely deformed granitoids with strong shape fabrics are concentrated in a 150 200 m wide zone parallel to the subvertical basement cover interface high fluid activity in this zone is indicated by 1 thickness and close spacing of foliation parallel quartz veins 2 abundant fluid inclusion trails in quartz 3 quartz c axis fabrics and 4 transformation of feldspar into phyllosilicates under middle greenschist facies metamorphic conditions away from this zone brittle ductile deformation in archaean granitoids caused grain size reduction of feldspar by fracturing and crystal plastic deformation of quartz indicating largely dry conditions strain was concentrated at the interface in a region of bulk horizontal shortening and linked kinematically to large scale shortening of the sudbury igneous complex and thrusting in the south range shear zone after early open buckling of the sudbury igneous complex reverse shearing in this zone may have been controlled by ductile deformation at the basement cover interface physical continuity of and age constraints on strain fabrics suggest that the south range shear zone represents a segment of a large ductile deformation zone which is most likely linked to the murray fault and on which higher grade rocks ascended between 1 85 and 1 23 ga ago

significance of lamination in toarcian lower jurassic shales from yorkshire great britain abstract lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes variations in types of lamination in toarcian lower jurassic shales of yorkshire great britain are related to changes in sedimentary processes x radiography petrography and scanning electron microscopy techniques reveal three lamination types in the dark grey grey shales and black jet rock and bituminous shales jurassic shales fine lamination is produced in deeper more offshore anaerobic conditions in which suspension settling dominates thick lamination indicates the influence of bottom flowing currents in shallow water wavy lamination is produced by benthic microbial mats the toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment the examples of various unique macro and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation

the late quaternary vegetational and climatic history of easter island easter island occupies an exceptionally isolated position in the south pacific ocean it is entirely volcanic and is famous for its giant statues late quaternary sediments have been investigated in three craters rano raraku rano aroi and rano kao giving a continuous record over the past 30 ka pollen records indicate that the island was formerly forested palynological and sedimentological evidence suggests a late pleistocene climate slightly cooler and drier than the present deforestation by people occurred mainly between 1200 and 800 yr bp this may have led to an ecological disaster and to the decline of the megalithic civilization the depauperation of the present native flora owes more to human activity than to isolation

charcoal fragments in surface samples following a fire and the implications for interpretation of subfossil charcoal data abstract following an uncontrolled fire in an area of heathland in sw england surface samples were taken from selected positions charcoal concentrations charcoal pollen ratio and size class frequencies were measured and the data from burned unburned and forest areas are compared charcoal concentrations show distinct variability between closely spaced samples but despite this differences are shown between the burned and unburned areas selected size classes are suggested as being appropriate for distinguishing between burned and unburned areas in palaeoecological studies while in need of replication these data should provide a basis for further studies of this type

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal