zn pb mineralisation in the silvermines district ireland a product of burial diagenesis carbonate sulphide cement stratigraphic relationships in the host rock and ore have been used to constrain the age of mineralisation at the silvermines zinc lead barium deposit the base metal sulphides post date planar dolomite and replace stylolites furthermore the pre mineralisation planar dolomites also replace stylolites these and other diagenetic observations indicate that the base metal sulphides formed at burial depths greater than 800 m but probably predate the variscan deformation since pressure shadows overgrow base metal sulphides this indicates that the sulphides are of epigenetic origin constraining the age of mineralisation to between the late chadian 347 ma and the late westphalian 307 ma however the most likely age for mineralisation based on widespread macro stylolite development is asbian 339 ma or younger no evidence of synsedimentary sulphides in the form of hydrothermal chimneys vent faunas or sulphides intergrown with marine cements was observed at silvermines mineralised breccias black matrix breccias late stage internal sediments and dissolution zones within the carbonate cements all appear to be produced by hydrothermal karsting that occurred during the mineralisation process fluid inclusion homogenisation temperatures for ore stage calcites up to 300 c approach the peak temperature estimates derived from regional maturation parameters 270 to 310 c from conodont alteration indices and vitrinite reflectance this suggests that homogenisation temperatures represent maximum heating temperatures probably during variscan time rather than mineralisation temperatures

late holocene vegetation dynamics and deforestation in rano aroi implications for easter island s ecological and cultural history abstract easter island rapa nui has been considered an example of how societies can cause their own destruction through the overexploitation of natural resources the flagship of this ecocidal paradigm is the supposed abrupt island wide deforestation that occurred about one millennium ago a few centuries after the arrival of polynesian settlers to the island other hypotheses attribute the forest demise to different causes such as fruit consumption by rats or aridity but the occurrence of an abrupt island wide deforestation during the last millennium has become paradigmatic in rapa nui we argue that such a view can be questioned as it is based on the palynological study of incomplete records owing to the existence of major sedimentary gaps here we present a multiproxy pollen charcoal and geochemistry study of the aroi core the first gap free sedimentary sequence of the last millennia obtained to date in the island our results show changing vegetation patterns under the action of either climatic or anthropogenic drivers or both depending on the time interval considered palm forests were present in aroi until the 16th century when deforestation started coinciding with fire exacerbation likely of human origin and a dry climate this is the latest deforestation event recorded so far in the island and took place roughly a century before european contact in comparison to other easter island records this record shows that deforestation was neither simultaneous nor proceeded at the same pace over the whole island these findings suggest that easter island s deforestation was a heterogeneous process in space and time and highlights the relevance of local catchment traits in the island s environmental and land management history

meteoric diagenesis below a submerged platform implications for δ13c compositions prior to pre vascular plant evolution middle ordovician alabama u s a abstract the middle ordovician chickamauga formation at red mountain expressway rme and tidwell hollow twh sections in alabama u s a has a complex early diagenetic history early diagenetic history of the buildup facies consisted of two phases of marine cementation separated by two generations of meteoric equant calcite with moldic dissolution separating equant calcite generations a third generation of meteoric equant drusy calcite is present after secondary marine diagenesis equant drusy calcite is interpreted as meteoric because its stable isotopic composition 13 c 0 1 to 1 6 18 o 4 8 to 7 3 is too variable to be accounted for by marine or mixing zone precipitation equant drusy calcite from buildup facies is mostly non luminescent and non ferroan this is unlike early ferroan equant calcite dull to bright luminescent from below the unconformity that overlies the chickamauga formation at rme meteoric diagenesis below the unconformity is unrelated to early diagenesis in the underlying buildup facies equant drusy calcite from the buildup facies at rme has a covariation of 13c and 18o values that forms a truncated inverted j and has elevated mg values these geochemical signatures indicate precipitation at a site that was distal from the recharge zone meteoric diagenesis at rme occurred during rising relative sea level and flow of meteoric fluids under a submerged platform is the only mechanism able to reconcile available stratigraphic petrologic and geochemical data ordovician meteoric 13c values from twh and other formations are slightly depleted 2 4 relative to coeval marine carbonate especially when compared with post silurian meteoric carbonate minor depletion of ordovician carbonate is the result of limited generation of light soil gas co2 before the development of vascular plants

the 1 75 1 68ga anorthosite mangerite alkali granitoid rapakivi granite suite from the northern north china craton magmatism related to a paleoproterozoic orogen abstract the amgrs is a suite of anorthosite mangerite alkali granitoid rapakivi granite in the northern north china craton ncc new zircon shrimp and laser ablation inductively coupled plasma mass spectrometry la icpms u pb dating of the damiao anorthosite changsaoying k feldspar granite lanying anorthosite and quartz syenite and the gubeikou k feldspar granite yielded emplacement ages of 1726 9 ma 1753 23 ma 1739 43 ma 1712 15 ma and 1692 19 ma respectively combined with previous geochronological data from the damiao norite and mangerite and shachang rapakivi granite it indicates that the whole amgrs was intruded between 1750 ma and 1680 ma the damiao anorthosites and norites exhibit a high mg and this decreases from mafic up to 63 to felsic t dm c ages ranging from 2 32 ga to 2 43 ga and 2 70 ga to 2 88 ga respectively this suggests that these rocks are the fractional crystallization products of one parental magma zircon hf and whole rock sr nd pb isotopic systematics combined with high la yb 10 and intermediate th ta ratios suggest that the parental magma of the amgrs could have been derived from em i lithosphere mantle enriched by recycled archean continent crustal materials accompanied by some assimilation of lower crustal components the mafic to felsic compositions of the amgrs are different from typical bimodal rocks formed in an anorogenic intra continent rift setting but resemble those emplaced during post collisional post orogenic extensional tectonic setting this is compatible with their age of

burial cementation in the devonian kaybob reef complex alberta canada abstract detailed analysis of the petrography and distribution of compositionally zoned ferroan calcite and dolomite cements in the devonian kaybob reef complex of alberta canada has demonstrated that porosity occlusion is predominantly a result of burial diagenesis to depths in excess of 4 km different but temporally related mechanisms of formation are indicated for the two cement types coarsely crystalline dolomite and coarsely crystalline calcite calcite cement precipitational history determined by correlation of compositional zones demonstrates that pressure solution along stylolites was the essential mechanism of calcite cementation in the reef interior and to a lesser extent in the reef slope facies zoned dolomite cements are in contrast the major cement type in the reef margi and reef slope facies a basinal source for dolomite precipitating fluids is indicated it is suggested that the composition of basin derived pore waters was controlled by temperature dependent clay mineral reactions as a function of progressive burial

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

vegetation dynamics at raraku lake catchment easter island during the past 34 000 years abstract easter island is a paradigmatic example of human impact on ecosystems the role of climate changes in recent vegetation shifts has commonly been rejected without proper assessment a palynological study of a long sediment core from raraku lake documents the vegetation dynamics for the last 34 ka and investigates their driving forces particularly the effects of climate variability on vegetation changes significant relationships between pollen assemblage changes and sedimentary and geochemical proxies demonstrate the rapid response of vegetation to lake crater basin hydrology and climatic changes the lake surroundings were occupied by an open mixed palm grove during the last glacial period poaceae and sophora increased at the expense of palms and triumfetta and coprosma practically disappeared in response to slightly wetter and or colder climate during the last glacial maximum palms and triumfetta thrived in a warmer and or drier climate during the deglaciation minor vegetation changes a slight increase in sophora and a drop in asteraceae and poaceae occurred between 13 2 and 11 8 cal ka bp and can be related to rapid changes in the younger dryas chronozone the increase in herbaceous taxa indicates a gradual shallowing of the lake and development of a mire during the holocene caused by sediment infilling and warmer and drier climate relatively rapid vegetation changes in the holocene were caused by climate and by plant succession on the expanding mire the rates of vegetation change observed in the mire were similar to those at the initial stages of human impact identified in a previous study these results reveal significant vegetation changes prior to human presence due to the interplay of climate variations temperature and moisture changes in lake basin form by infilling and intrinsic dynamics of plant succession hence the potential contribution of these factors in vegetation shifts during the period of human presence should not be neglected

palaeoclimates in central and south america since 18 000 bp based on pollen and lake level records abstract the last 18 ka of palaeoclimates are discussed at 3 ka intervals based on palaeoenvironmental changes shown in pollen and lake level records from central and south america a total of 61 pollen records fulfill the requirements of continuity and chronology to be used in this synthesis 8 records from tropical and subtropical lowlands in central and south america 7 records from the central american highlands 26 records from the high andes north and south of the equator 2 records from the southern subtropics and 18 from the southern andes and subantarctic islands palaeoclimatic interpretation of the pollen records is semiquantitative based on bioclimatic parameters such as e g elevational temperature gradients or latitudinal precipitation gradients that can be related to vegetation zonation additional palaeoclimatic information is obtained from lake level records derived either from dated shorelines or from the limnological history of lake sediment sections large scale palaeoclimatic comparison of the proxy data records indicates that full and late glacial climates throughout central and south america were cooler than today by about 4 to 5 c but that moisture patterns showed regional differentiation thus in both the southern subtropics and high latitudes in southern chile conditions were substantially moister than today during full and late glacial times whereas everywhere else conditions were far drier than today in terms of palaeocirculation this scenario can be interpreted as a poleward shift of the subtropical as well as the westerly circulation a scenario that has been suggested by palaeoclimatic simulations from general circulation models gcm another major palaeoclimatic aspect predicted by the gcm simulations is the suppressed early holocene summer monsoon in the southern subtropics although proxy records are few from this zone their palaeoenvironmental history during that time shows a period of aridity that would support the model one of the most controversial aspects of south american palaeoclimates concerns the existence of a younger dryas equivalent a cold period between 11 and 10 ka bp based on the existing data from south america that show a great diversity of palaeoclimatic trends the concept of an interval that is characterized by the same climatic signal as documented for the north atlantic seems too simplistic moreover at this point only very few records have been analysed in sufficient detail to yield unambiguous climatic information for the interval in question the principal outcome of this palaeoenvironmental and palaeoclimatic synthesis is the better understanding of the type and quality of data available at present and the realization of regions and periods where much more and concerted effort is needed to address problems of intra and interhemispheric palaeoclimatic correlations only then can questions concerning the mechanism of climatic change be tackled successfully

a late quaternary record of environmental change and human impact from new caledonia a late quaternary vegetation record is presented from a lowland site on the leeward southwest coast of new caledonia plum swamp is a backswamp on the plum river at around 10 m a s l just within the ultramafic terrain that dominates the southern third of new caledonia pollen analysis charcoal analysis radiocarbon dating and stratigraphic analysis are employed to reconstruct the vegetation and sedimentary history of the valley the vegetation record commences at around 20 000 yr bp and shows that from this time up until the late holocene the valley was forested the greater representation of taxa more prevalent at higher altitudes during the late glacial suggests a response to cooling and an enrichment of the lowland forest with more montane elements the late glacial transition between 14 000 and 9000 yr bp is a period of instability within the valley when vegetation is disturbed by fire forest recovers after this and there is increasing stability until the arrival of people in the late holocene at around 3000 yr bp the initial colonisers of new caledonia had a profound effect upon the vegetation of the valley converting the lowland forest to a stunted and species poor maquis on the ultramafic sediments and melaleuca woodland on the non ultramafic substrates however sedimentary processes are relatively unchanged during this time dramatic geomorphic change does occur in the catchment though during the latter part of the 20th century as a consequence of mining q 2001 elsevier science b v all rights reserved

the last glacial maximum climatic conditions on easter island abstract the aim of this paper is to refine previous estimates of last glacial maximum lgm climatic conditions for easter island samples were analysed for fossil pollen from the lower half of a 13 40 m sediment core rra5 this part of the core includes a time span from ca 28 000 10 000 14 c bp the results show that during this period there were three different climatic conditions first a time span from ca 28 000 23 200 14 c bp with slightly cooler and probably drier conditions relative to present day second a more cool and dry climatic condition from ca 23 200 14 700 14 c bp the second time span had two peak points at ca 22 100 and 17 150 14 c bp it seems that the coolest and driest conditions occurred at 17 150 14 c bp third a warm and wet climate started at ca 15 000 14 c bp and continued until the end of the period studied 10 000 14 c bp in all the time covered in this study there was an inverse relationship between values of palmae and poaceae while poaceae and tubuliflorae shrubs show similar variations the temperature estimations that are presented by different authors based on oxygen isotopes are for approximately 4 c cooling at the lgm however the empirical values derived from the pollen evidence suggest only ca 1 9 c cooling this is in agreement with recently obtained values from tropical lowlands

macrofossils in raraku lake easter island integrated with sedimentary and geochemical records towards a palaeoecological synthesis for the last 34 000 years abstract macrofossil analysis of a composite 19 m long sediment core from rano raraku lake easter island was related to litho sedimentary and geochemical features of the sediment strong stratigraphical patterns are shown by indirect gradient analyses of the data the good correspondence between the stratigraphical patterns derived from macrofossil correspondence analysis and sedimentary and geochemical data principal component analysis shows that macrofossil associations provide sound palaeolimnological information in conjunction with sedimentary data the main taphonomic factors influencing the macrofossil assemblages are run off from the catchment the littoral plant belt and the depositional environment within the basin five main stages during the last 34 000 calibrated years bp cal yr bp are characterised from the lithological geochemical and macrofossil data from 34 to 14 6 cal kyr bp last glacial period the sediments were largely derived from the catchment indicating a high energy lake environment with much erosion and run off bringing abundant plant trichomes lichens and mosses into the centre of raraku lake during the early holocene the infilling of the lake basin and warmer conditions favoured the growth of a littoral plant belt that obstructed terrigenous input cladoceran remains and solanaceae seeds are indicative of reduced run off and higher values of n and organic c indicate increased aquatic and catchment productivity from 8 7 to 4 5 cal kyr bp a swamp occupied the entire basin the increase of cyperaceae seeds reflects this swamp development and with oribatid mites and coleopteran remains indicates a peaty environment and more anoxic conditions in raraku at around 4 5 cal kyr bp dry conditions prevented peat growth and there is a sedimentary hiatus about 800 cal yr bp peat deposition resumed finally in the last few centuries a small lake formed within the surrounding swamp evidence of human activity is recorded in these uppermost sediments

the late quaternary decline and extinction of palms on oceanic pacific islands late quaternary palaeoecological records of palm decline extirpation and extinction are explored from the oceanic islands of the pacific ocean despite the severe reduction of faunal diversity coincidental with human colonisation of these previously uninhabited oceanic islands relatively few plant extinctions have been recorded at low taxonomic levels recent faunal extinctions on oceanic islands are concentrated in larger bodied representatives of certain genera and families fossil and historic records of plant extinction show a similar trend with high representation of the palm family arecaceae late holocene decline of palm pollen types is demonstrated from most islands where there are palaeoecological records including the cook islands fiji french polynesia the hawaiian islands the juan fernandez islands and rapanui a strong correspondence between human impact and palm decline is measured from palynological proxies including increased concentrations of charcoal particles and pollen from cultivated plants and invasive weeds late holocene extinctions or extirpations are recorded across all five of the arecaceae subfamilies of the oceanic pacific islands these are most common for the genus pritchardia but also many sedis fossil palm types were recorded representing groups lacking diagnostic morphological characters

multi proxy evidence of late holocene human induced environmental changes at lake pupuke auckland new zealand abstract new zealand was the last major landmass in the world to be colonised by people despite the short time depth of human presence in the country there is ongoing debate about the date of earliest arrival of people that resulted in the emergence of two contrasting colonisation hypotheses the early hypothesis and the short prehistory to decide between both hypotheses we employed a range of multi proxy investigations geochemistry stable isotopes and mineral magnetism on a lacustrine sequence from lake pupuke a maar lake in the city of auckland and an area potentially among the first places in new zealand to have been colonised by early people the environmental history reconstructed from the multi proxy evidence identified a clear lack of catchment disturbance from c 2000 b p until several decades before the eruption of the rangitoto volcano the nature and abruptness of disturbance unambiguously point to anthropogenic forcings and are likely to mark the onset of prehistoric human colonisation at the site linear interpolation between independently dated tephrochronostratigraphic marker beds present in the sediments allowed to date this event to c 610 cal yr b p this date is in compliance with the short prehistory for this region

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

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

deep burial dolomitization in the ordovician ellenburger group carbonates west texas and southeastern new mexico abstract from western texas and southeastern new mexico core samples of shallow subtidal and peritidal carbonates in the ellenburger group lower ordovician were examined to investigate the effects of deep burial on diagenesis at present the burial depth of samples ranges from 6 000 ft 1 5 km to 23 000 ft 7 0 km below 10 000 ft 3 0 km carbonates are exclusively dolostones showing evidence of deep burial dolomitization such as the presence of coarse crystalline dolomite xenotopic texture homogeneous cathodoluminescence high fluid inclusion homogenization temperatures and light oxygen isotope compositions locally neomorphism of older fine crystalline dolomite occurs however the preservation of depositional textures in coarse crystalline xenotopic dolomite indicates a nonobliterative replacement origin in deep burial environments millimeter size crystals of euhedral saddle dolomite commonly fill vugs and fractures the mg 2 ions in the nonferrous dolomites are probably derived from basinal brines via high porosities and fractures higher temperatures and longer reaction times coupled with the addition of mg 2 ions from circulating waters are apparently responsible for deep burial dolomitization

tectonics of the southern and central appalachian internides the appalachian orogen was constructed along the ancient precambrian continental margin of eastern north america by a series of compressional events that began in the ordovician and episodically spanned much of the paleozoic era the processes of accretion of suspect and exotic terranes together with terrane collision and ultimately completion of the wilson cycle by continent continent collision resulted in construction of the appalachian orogen figure 1 these paleogeographic elements are rep resented by the various lithotectonic units visible today in the southern and central appalachians figure 2 these subdivisions represent the late precambrian rifted margin and early paleozoic platform that were formed directly upon north american grenvillian basement cumberland allegheny plateau valley and ridge and western blue ridge the offshore north american slope rise assemblage hamburg klippe southern appalachian eastern blue ridge and inner piedmont and higher thrust sheets of the maryland northern virginia piedmont and the exotic carolina or avalon and wilmington terranes the carolina ter rane contains the alleghanian high grade metamorphic core these elements form the basis for this analysis and review of the present state of knowledge of the tectonic history of the southern and central appalachian internides the appalachian orogen has been the subject of study by geologists at least since the early nineteenth century early fundamental concepts such as the geosynclinal theory of mountain building dana 1873 hall 1883

holocene environmental history of a small mediterranean island in response to sea level changes climate and human impact the aim of this study is to investigate human climate environment interactions in a small mediterranean island comparison between palynological and palaeoentomological data from the greco pond cavallo island southern corsica reveals that the island was first covered by a more or less open erica arborea pasture woodland from ca 7000 to 6100 cal yr b p grazing animals from 7000 to 6200 cal yr b p followed by a spreading of ficus carica marked by the bark beetle hypoborus ficus from ca 6100 to 5750 cal yr b p suggest that human activities could be implicated in the e arborea forest opening from ca 5500 cal yr b p a regional expansion of q ilex was recorded but an open landscape with thermophilous and drought tolerant plants locally took place from ca 4700 cal yr b p onward pastoral and agricultural biomarkers pollen npp and insect together with archaeological evidence indicate that human activities were involved in the installation of a lasting open vegetation simultaneously the effects of the holocene relative sea level rise on the coastal wetland are recorded 1 freshwater conditions prevailed in the greco pond since 7000 cal yr b p at least 2 the first evidence of salt marsh development dates back to ca 4500 cal yr b p 3 a strong increase of salinity with marine intrusions were recorded at ca 3700 cal yr b p while a decline in aquatic insect diversity occurred and 4 a phase of sand dune formation was recorded from ca 2000 cal yr b p onward our results suggest that if large scale climatic trend such as the holocene relative sea level rise could affect coastal ecosystem effects of human activities could play the leading role in vegetation and terrestrial beetle assemblage changes in a small island context

formation of coarsely crystalline hydrothermal dolomite reservoirs in the presqu ile barrier western canada sedimentary basin late stage coarsely crystalline replacement dolomite and associated saddle dolomite cement form a widespread diagenetic facies in the middle devonian presqu ile barrier that extends southwestward from pine point to the subsurface of the foothills in northeastern british columbia these dolomites create hydrocarbon reservoirs in otherwise tight limestones in the subsurface of the northwest territories and northeastern british columbia and host mississippi valley type deposits at pine point the coarsely crystalline replacement dolomite and saddle dolomite cement are interpreted to have formed during burial because they replace blocky sparry calcite cements occur continuously across the sub watt mountain unconformity postdate stylolites and earlier replacement dolomites and overlap sulfide mineralization the dgr18o values of both replacement and saddle dolomites increase eastward updip along the presqu ile barrier from 16 pmil pdb in the deeper subsurface of northeastern british columbia to 7 pmil pdb at pine point whereas the corresponding homogenization temperatures of saddle dolomite fluid inclusions decrease from 178 to 92 c the 87sr 86sr ratios of coarsely crystalline and saddle dolomites decrease eastward along the pres u ile barrier from about 0 7106 in the subsurface of northeastern british columbia to 0 7081 at pine point these geochemical trends suggest a possible basin scale migration of hot radiogenic dolomitizing fluids updip eastward along the presqu ile barrier such large scale fluid movements probably were related to western canada sedimentary basin tectonic compression and sedimentary loading which occurred at least twice during early burial between the late devonian and early carboniferous and during deep burial between the late jurassic and early tertiary

drought vegetation change and human history on rapa nui isla de pascua easter island abstract stratigraphic records from lake sediment cores and slope deposits on rapa nui document prehistoric human impacts and natural environmental changes a hiatus in sedimentation in rano raraku suggests that this lake basin dried out sometime after 4090 4410 cal yr bp and refilled only decades to centuries before ad 1180 1290 widespread ecosystem changes caused by forest clearance by polynesian farmers began shortly after the end of this drought terrestrial sections show a chronology of burning and soil erosion similar to the lake cores although changing sediment types and shifts in the pollen rain suggest that droughts occurred earlier in the holocene as yet there is no evidence for droughts occurring after ad 1180 1290 the timing of the agricultural colonization of rapa nui now seems well established at ca ad 1200 and it was accompanied by rapid deforestation that was probably exacerbated by the island s small size its droughty climate and the rarity of primeval fires detailed records of a large interval of rapa nui s ecological history remain elusive due to the drought hiatus in the rano raraku sediment record we find no evidence for a rat outbreak impact on rapa nui s vegetation preceding anthropogenic forest clearance

effects of syn pandemic fire reduction and reforestation in the tropical americas on atmospheric co2 during european conquest abstract a new reconstruction of late holocene biomass burning in the tropical americas is consistent with the expansion of fire use by mesoamerican and amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years bp the marked reduction of biomass burning after 500 years bp a unique feature of the fire history of the tropical americas relative to other regions of the globe is synchronous with the collapse of the american indigenous population during pandemics accompanying european conquest we predict that fire reduction contemporaneous with pandemics in the tropical americas was associated with massive forest regeneration on 5 105 km2 of land and sequestration of 5 10 gt c into the terrestrial biosphere which contributed to the 2 global reduction in atmospheric co2 levels and the 0 1 increase in 13c of atmospheric co2 from 1500 to 1750 a d this study 1 builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14c dates to resolve features of the late holocene biomass burning record in the tropical americas and 2 corroborates the hypothesis advanced by ruddiman ruddiman w f 2003 the anthropogenic era began thousands of years ago climatic change 61 261 293 ruddiman w f 2005 plows plagues and petroleum princeton university press princeton new jersey that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric co2 concentration during the past millennium

on balanced and unbalanced accommodation peat accumulation ratios in the cretaceous coals from gates formation western canada and their sequence stratigraphic significance coal composition was investigated by means of photometric and maceral analyses on closely spaced lithotype based strip samples over the full thickness of several paralic coal seams from the cretaceous gates formation of the western canadian sedimentary basin the aim of this investigation was to test various methods of identifying accommodation trends in coal and use them to refine sequence stratigraphic interpretation of continental sediments conventional sequence stratigraphy derives its subdivisions and significant surfaces from the records left by relative sea level oscillations these records either do not project into the continental realm or are difficult to recognise in clastic non marine sediments paralic coal seams have been selected to study this problem because they are not entirely removed from marine influence and compared with most inorganic deposits coal has stored a greater wealth of information that can be analysed at a higher level of resolution the study has led to the identification of five new surfaces with chronostratigraphic potential in the sequence stratigraphic analysis of non marine sediments two of these surfaces called paludification surface pas and terrestrialisation surface tes occur at the bases of the investigated coal seams while two other surfaces referred to as non marine flooding surface nfs and give up transgressive surface guts form the tops of the coal the fifth and probably most important new surface called the accommodation reversal surface ars is independent of any particular facies and may either coincide with some of the other surfaces or occur separately the proportion of detrital minerals has been used as the chief discriminator between different mire types and accommodation trends other useful indicators of mire type and peat dispersal have been the proportions of sporinite and inertodetrinite as well as some derived maceral and or mineral ratios e g the groundwater influence index and the tissue preservation index isometamorphic variations of telovitrinite reflectance and fluorescence as well as their coefficients of variation were also found to contribute to the identification of cyclic shifts between balanced and unbalanced accommodation peat accumulation ratios some of these cycles which are backed up by clastic stratigraphy appear to correspond to the development of shallowing upward and deepening upward parasequences superimposed high frequency low amplitude perturbations in the coal cycles relate to smaller scale accommodation cycles of sub parasequence level not always recognised in non marine strata these sub parasequence coal cycles do not always continue the shallowing upward trend typical of conventional parasequences several coals were found to contain stacks of small scale cycles with upward increasing accommodation signatures either in their lower or upper halves or over the whole seam section

saddle dolomite as a by product of chemical compaction and thermochemical sulfate reduction petrographic stable and radiogenic isotope trace element and fluid inclusion data from the devonian nisku reef trend in the subsurface of alberta canada suggest that saddle dolomite was a by product of chemical compaction and thermochemical sulfate reduction in subsiding dolomitized rocks furthermore thermochemical sulfate reduction may be representative of other processes that increase the amount of saddle dolomite via an increase in carbonate alkalinity the data also confirm that saddle dolomite is most likely to form at elevated temperatures from hypersaline brines

a late quaternary pollen record from ka au crater o ahu hawai i abstract a pollen record from ka au crater o ahu hawai i contains evidence for changes in vegetation and climate since about 28 000 14c yr b p zone 1 ca 28 100 ca 22 800 14c yr b p has pollen of dry to mesic forest species including pipturus type dodonaea viscosa acacia koa chenopodium oahuense claoxylon sandwicense myrsine and metrosideros type in zone 2 ca 22 800 ca 16 200 14c yr b p myrsine and coprosma increase with herbs fern allies and grammitidaceae suggesting open canopies zone 3 ca 16 200 ca 9700 14c yr b p has pollen of wet forest species including freycinetia arborea abundant pritchardia and metrosideros type zone 4 ca 9700 ca 7000 14c yr b p is similar with less pritchardia and more metrosideros type climate reconstruction was based on modern climatic ranges of flowering plants and an index derived from abundance of pollen in surface samples both methods agree on a qualitative reconstruction although the ages are poorly constrained 28 000 25 000 14c yr b p cool and dry 25 000 23 000 14c yr b p dry and warmer 23 000 20 000 14c yr b p moderately dry with declining temperature 20 000 16 000 14c yr b p moderately dry and cool 16 000 9000 14c yr b p warm and wet 9000 7000 14c yr b p warm and possibly drier lower precipitation at ka au crater during the late glacial period and last glacial maximum is consistent with the interpretation that the north pacific subtropical anticyclone was south of its present position the pollen derived temperature index yields an estimate of 3 5 c temperature depression during the last glacial maximum

natural and anthropogenic drivers of cultural change on easter island review and new insights abstract easter island rapa nui is a remote pacific island known for its megalithic statues the moai built by an ancient culture which disappearance is still debated theories claiming for either self destruction ecocide of this ancient culture or an eventual genocide after the european contact have been the most popular anthropogenic drivers have been traditionally preferred as causes of this major cultural shift whereas climatic changes have been dismissed or underrated however the latest findings suggest that the topic is more complex than formerly thought and demand a more holistic perspective this paper reviews the main paleoclimatic paleoecological archaeological and historical evidence of the major rapanui cultural shift leading to the end of the moai building civilization and uses an integrated approach to analyze its timing and potential causes the disappearance of the ancient eastern island culture that erected the moai was a dramatic cultural shift with significant changes in lifestyle socio political organization religious performance art and also in the geographical settlement of the cultural core of the rapanui society the ancient society represented by the so called ancient cult or moai cult was centered on the rano raraku crater to the east of the island whose soft volcanic rocks tuff where suitable for moai carving this society was replaced by the birdman cult society based on rano kao to the westernmost end of the island the assumed date for such shift is uncertain ranging between mid 16th and late 18th centuries it is suggested that such geographical change as well as the associated societal transformations may have been the result of a combination of climatic ecological and cultural drivers and events the latest paleoecological reconstructions show that the rano raraku catchment was deforested by ad 1450 and the lake inside dried out by ad 1550 owing to an intense climatic drought this would have caused a landscape deterioration transforming the raraku catchment into a wasteland devoid of freshwater and unsuitable for human life and the cultural flourishment that characterized the ancient cult society the drought lasted for about a century and a half and would have forced the rapanuis to look for alternative freshwater sources the only feasible option was the freshwater lake inside the then forested rano kao crater where the ceremonial village of orongo the center of the birdman cult was funded by ad 1600 the kao crater is made of hard volcanic rocks basalts unsuitable for moai carving by the neolithic rapanui culture unaware of metals which would have contributed to the end of the moai building phase deforestation and drought would have led to a general demographic decline the shift from the rigid socio political organization of the ancient cult to the more flexible system characteristic of the birdman cult could be viewed as a cultural adaptation to changing environmental conditions the occurrence of a further rather catastrophic genocide caused by slave trading and epidemic diseases occurred shortly after the european contact ad 1722 has been documented historically therefore the rapanui civilization has undergone at least two cultural crises caused by natural and anthropogenic drivers a complex synergistic scenario like that proposed here can conciliate multidisciplinary lines of evidence formerly used to defend more simplistic and apparently contradictory hypotheses of cultural change

dolomite from clay in argillaceous or shale associated marine carbonates abstract postcompactional late stage ferroan dolomite commonly occurs as 1 finely disseminated rhombic microspar in argillaceous lime mudstone 2 sparry cement within voids in argillaceous carbonates and 3 sparry cement within carbonates adjacent to marine shales the distribution and abundance of these dolomites correspond with that of clay deposited in the marine environment and cannot easily be explained by alternative models of dolomite formation conversion of smectite to illite during burial is a common diagenetic process which is capable of releasing large amounts of fe mg ca na and si sandstone petrologists have emphasized the significance of this process in generating quartz cements in sandstone shale sequences however the potential of this conversion for producing postcompactional dolomite cement in limestone shale sequences or in argillaceous limestones has been neglected smectite illite conversion is here invoked as the source of ions that formed late stage postcompactional dolomites in examples of the pennsylvanian of oklahoma kansas missouri and iowa the devonian of iowa and the ordovician of oklahoma the smectite illite conversion model for generating dolomite may be widely applicable to many other ex mples of late stage dolomitization it should prove useful in predicting the distribution of late stage dolomite cement that reduces reservoir quality and may prove useful for estimating the timing of hydrocarbon migration relative to carbonate cementation

vegetation changes and human settlement of easter island during the last millennia a multiproxy study of the lake raraku sediments earlier palynological studies of lake sediments from easter island suggest that the island underwent a recent and abrupt replacement of palm dominated forests by grasslands interpreted as a deforestation by indigenous people however the available evidence is inconclusive due to the existence of extended hiatuses and ambiguous chronological frameworks in most of the sedimentary sequences studied this has given rise to an ongoing debate about the timing and causes of the assumed ecological degradation and cultural breakdown our multiproxy study of a core recovered from lake raraku highlights the vegetation dynamics and environmental shifts in the catchment and its surroundings during the late holocene the sequence contains shorter hiatuses than in previously recovered cores and provides a more continuous history of environmental changes the results show a long gradual and stepped landscape shift from palm dominated forests to grasslands this change started c 450 bc and lasted about two thousand years the presence of verbena litoralis a common weed which is associated with human activities in the pollen record the significant correlation between shifts in charcoal influx and the dominant pollen types suggest human disturbance of the vegetation therefore human settlement on the island occurred c 450 bc some 1500 years earlier than is assumed climate variability also exerted a major influence on environmental changes two sedimentary gaps in the record are interpreted as periods of droughts that could have prevented peat growth and favoured its erosion during the medieval climate anomaly and the little ice age respectively at c ad 1200 the water table rose and the former raraku mire turned into a shallow lake suggesting higher precipitation evaporation rates coeval with a cooler and wetter pan pacific ad 1300 event pollen and diatom records show large vegetation changes due to human activities c ad 1200 other recent vegetation changes also due to human activities entail the introduction of taxa e g psidium guajava eucalyptus sp and the disappearance of indigenous plants such as sophora toromiro during the two last centuries although the evidence is not conclusive the american origin of v litoralis re opens the debate about the possible role of amerindians in the human colonisation of easter island

u pb baddeleyite ages distribution and geochemistry of 925 ma mafic dykes and 900 ma sills in the north china craton evidence for a neoproterozoic mantle plume numerous neoproterozoic mafic dykes referred to as the dashigou swarm are identified in the central and southeastern parts of the north china craton ncc they are 305 010 degrees trending dykes with widths of similar to 10 100 m and exposed lengths of several to 10 km precise u pb isotope dilution thermal ionization mass spectrometry id tims measurements on baddeleyite grains separated from three dykes yield 207 pb 206 pb average ages of 924 0 3 7 ma dashigou dyke 921 8 2 6 ma yangjiaogou dyke and 925 8 1 7 ma taohuagou dyke baddeleyite grains from a late stage pegmatite vein in the dashigou dyke were analyzed by secondary ion mass spectrometry sims methods these yield a 207 pb 206 pb average age of 920 4 5 7 ma the dashigou dyke swarm exhibits an overall radiating geometry the overall fan angle is about 60 degrees with a focal point located along the southern margin of the eastern ncc where a large ca 900 ma sill swarm was previously recognized the rift system hosting these slightly younger sills named the xu huai rift system could represent two breakup parallel arms of a rift rift rift triple junction related to the initiation of the magma center that produced the dashigou dykes the sills have similar characteristics and could be cogenetic with the dashigou dykes the dashigou dykes are coarse grained composed mainly of clinopyroxene and plagioclase feldspar with or without olivine one of the most primitive dykes has 47 79 wt sio 2 6 41 wt mgo 1 38 wt tio 2 17 77 wt al 2 o 3 10 47 wt cao and 0 62 wt k 2 o it shows slight enrichment in light rare earth elements and a slightly positive eu eu anomaly 1 1 and is slightly depleted in high field strength elements compared to neighboring elements on a primitive mantle normalized spidergram the dashigou dykes show some similarities with enriched mid ocean ridge basalts e morb or ocean island basalts oib and have epsilon nd t values of 1 8 to 3 1 and 87 sr 86 sr t values of 0 7019 0 7047 t 920 ma all these characteristics indicate that they are not likely derived from the ancient lithospheric mantle under the ncc but rather from a mantle source below in the asthenosphere this 925900 ma magmatism represents a second sub lithospheric mantle upwelling event following the 1780 1730 ma event that occurred shortly similar to 70 ma after the formation of the subcontinental lithospheric mantle sclm therefore the sclm of the ncc was multiply metasomatized during asthenospheric upwellings at least at 1780 1730 and 925 900 ma before most of its eastern part was finally removed during the mesozoic collectively these similar to 925 ma dykes and similar to 900 ma sills constitute a large igneous province lip with an areal extent of about 0 5 mkm 2 and a diameter of about 1000 km this lip probably resulted from a neoproterozoic mantle plume centered along the present southern margin of the eastern ncc and probably resulted in the break off and rifting away of a separate crustal block we speculate that this conjugate block could have been the combined sao francisco congo craton on the basis of precisely matched ages for the bahia dykes sao francisco craton and gangila mayumbian volcanic associations western part of the congo craton c 2011 elsevier b v all rights reserved less

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

burial cementation in the swan hills formation devonian rosevear field alberta canada abstract saddle dolomite anhydrite and coarsely crystalline late mosaic calcite cements in the devonian swan hills formation at the rosevear field in alberta canada are interpreted from petrographic and geochemical evidence as the products of burial diagenesis these inferred burial cements are commonly found as a partial to complete filling of moldic and vuggy porosity in massive replacement dolostones fluid inclusions th 125 159 c tm 18 to 22 c 87sr 86sr ratios 0 7101 0 7115 enrichment in ba and zn and light 18o values 6 to 11 2 pdb suggest that saddle dolomite precipitated from hot radiogenic brine with salinities six times greater than seawater ions for saddle dolomite precipitation may have been sourced from off reef shales the precambrian basement middle devonian halite mesozoic clastics and swan hills replacement dolomite undergoing pressure solution in the presence of a normal paleogeothermal gradient 30 c km saddle dolomite would have formed in the late cretaceous paleocene at depths of 3 5 km this time corresponds to the emplacement of gas at the rosevear field dolomite hosted anhydrite cement with nonradiogenic 87sr 86sr 0 7083 and low 34s compositions 15 to 23 cdt has been quantitatively modeled using a two component mixing equation to constrain fluid and ion sources the results indicate that ions for cementation were derived from fluids that passed through and dissolved middle devonian anhydrite this produced a sr rich brine with nonradiogenic 87sr86sr and low 34s these fluids mixed with radiogenic formation water already in the reservoir to precipitate anhydrite cement with the observed isotopic composition fluid inclusions th 90 to 170 c tm 6 to 17 c and elevated 87sr 86sr compositions 0 7105 0 7173 in coarsely crystalline late mosaic calcite support precipitation during the hydrological transformation of the western canada basin into a topographically controlled flow regime the reduced precipitation temperatures of some fluid inclusions in late mosaic calcite compared to saddle dolomite may be attributed to the decrease in western basin paleogeothermal gradients following the laramide orogeny the presence of calcitized anhydrite coarsely crystalline calcite with light 13c values 5 4 to 13 2 pdb s enriched pyrite and 8 h2s in reservoir gases provide evidence for thermochemical sulfate reduction during burial diagenesis at rosevear

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

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

expansion of magellanic moorland during the late pleistocene palynological evidence from northern isla de chiloe chile the late quaternary vegetation of northern isla de chiloe is inferred from palynological analysis of a section in the rio negro drainage 42 03 s 73 50 w at ca 30 500 yr b p maxima of astelia and donatia occurred suggesting wetland development from that time until ca 27 000 yr b p steppe indicators such as compositae gramineae dominated suggesting drier conditions after 27 000 yr b p the moorland shrub dacrydium gradually increased reaching a maximum by 18 000 yr b p at this time astelia increased again suggesting development of cushion bog during cold and wet conditions the glacial postglacial transition is characterized by a marked change from peaty sediments to clays a decrease in the cushion bog flora and the prevalence of gramineae compositae and swamp taxa this vegetation prevailed until ca 7000 yr b p when forest taxa became dominant the floristic pattern inferred from the pollen spectra of the rio negro section suggests that the late pleistocene vegetation of chiloe resembled modern magellanic moorland vegetation 52 56 lat s based on climatic conditions presently associated with magellanic moorland its occurrence in chiloe at low elevations during the late pleistocene implies a decrease in average temperature of at least 4 c and an increase in annual precipitation of at least 1500 mm

environmental processes in rano aroi easter island peat geochemistry forced by climate variability during the last 70kyr abstract we analyze the geochemistry of rano aroi mire record easter island using bulk peat composition c n s and stable isotopes 13c 15n 34s and major minor and trace elemental compositions obtained by icp aes al ti zr sc v y fe mn th ba ca mg and sr peat geochemistry and the pollen record are used to reconstruct the environmental changes during the last 70 kyr bp principal component analysis on icp aes data revealed that three main components account for the chemical signatures of the peat the first component characterized by lithogenic elements combined signal of v al sc y cr cd ti zr and cu evidences long term changes in the basal fluxes of mineral material into the mire this component in combination with stable isotopes and pollen data suggests a link between soil erosion and vegetation cover changes in the rano aroi watershed the second component is identified by the signal of fe mn th ba zr and ti and is indicative of strong runoff events during enhanced precipitation periods the third component tied mainly to ca sr and mg reflects a strong peat oxidation event that occurred during an arid period with more frequent droughts sometime between 39 and 31 kyr bp correlation coefficients and a multiple regression model pcr analysis between peat organic chemistry and the principal components of icp aes analysis were calculated isotope chemistry of the peat organic matter further contributes to define rano aroi environmental history 13c data corroborates a vegetation shift documented by the palynological record from c4 to c3 between 55 and 45 cal kyr bp the 15n record identifies periods of changes in mire productivity and denitrification processes while the 34s peat signature indicates a marine origin of s and significant diagenetic cycling the geochemical and environmental evolution of rano aroi mire is coherent with the regional climatic variability and suggests that climate was the main forcing in mire evolution during the last 70 kyr bp the coupling of geochemical and biological proxies improves our ability to decipher depositional processes in tropical and subtropical peatlands and to use these sequences for paleoenvironmental and paleoclimate reconstructions

glacial to holocene climate changes in the se pacific the raraku lake sedimentary record easter island 27 s abstract easter island se pacific 27 s provides a unique opportunity to reconstruct past climate changes in the south pacific region based on terrestrial archives although the general climate evolution of the south pacific since the last glacial maximum lgm is coherent with terrestrial records in southern south america and polynesia the details of the dynamics of the shifting westerlies the south pacific convergence zone and the south pacific anticyclone during the glacial interglacial transition and the holocene and the large scale controls on precipitation in tropical and extratropical regions remain elusive here we present a high resolution reconstruction of lake dynamics watershed processes and paleohydrology for the last 34 000 cal yrs bp based on a sedimentological and geochemical multiproxy study of 8 cores from the raraku lake sediments constrained by 22 ams radiocarbon dates this multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake high lake levels and clastic input dominated sedimentation in raraku lake between 34 and 28 cal kyr bp sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the glacial period between 28 and 17 3 cal kyr bp including the lgm period colder conditions contributed to a reduction of the tree coverage in the island the coherent climate patterns in subtropical and mid latitudes of chile and eastern island for the lgm more humid conditions suggest stronger influence of the antarctic circumpolar current and an enhancement of the westerlies the end of glacial period occurred at 17 3 cal kyr bp and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments deglaciation termination 1 between 17 3 and 12 5 cal kyr bp was characterized by an increase in lake productivity a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels dominance of organic deposition and algal lamination the timing and duration of deglaciation events in easter island broadly agree with other mid and low latitude circum south pacific terrestrial records the transition to the holocene was characterized by lower lake levels the lake level dropped during the early holocene ca 9 5 cal kyr bp and swamp and shallow lake conditions dominated till mid holocene partially favored by the infilling of the lacustrine basin during the mid to late holocene drought phases led to periods of persistent low water table subaerial exposure and erosion generating a sedimentary hiatus in the raraku sequence from 4 2 to 0 8 cal kyr bp the presence of this dry mid holocene phase also identified in low andean latitudes and in patagonian mid latitudes suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by el nino like dominant conditions have occurred at a regional scale the palm deforestation of the easter island attributed to the human impact could have started earlier during the 4 2 0 8 cal kyr bp sedimentary gap our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the polynesian people to the island if it occurred at ca ad 800 it coincided with the warmer conditions of the medieval climate anomaly whereas if it took place at ca ad 1300 it was favored by enhanced westerlies at the onset of the little ice age changes in land uses farming intensive cattle during the last century had a large impact in the hydrology and limnology eutrophication of the lake

alteration of early formed dolomite during shallow to deep burial mississippian mission canyon formation central to southwestern montana dolomite in the mississippian mission canyon formation osagean to middle meramecian of central and southwestern montana precipitated during multiple episodes of dolomitization and or recrystallization the earliest generation of dolomite most likely precipitated from evaporated sea water in near surface diagenetic environments when the mission canyon platform intermittently aggraded to sea level this dolomite has relatively positive delta sup 18 o values minus 1 5 to 7 5 and typically is nonstoichiometric and trace element enriched a second generation of dolomite has very negative delta sup 18 o values minus 11 2 to minus 1 5 and always is stoichiometric and trace element depleted dolomite with delta sup 18 o values minus 6 8 is in the upper 100 180 m of the mission canyon formation beneath a regional post mission canyon unconformity and karst surface that extends across the entire study area dolomite depleted in sup 18 o may have 1 precipitated initially in a regional mixing zone during post mission canyon subaerial exposure and karstification 2 precipitated at elevated temperatures during later diagenesis or 3 recrystallized from an earlier generation of dolomite during later shallow to deep burial diagenesis very negative delta sup 18 o values and low trace element contents for the second generation of dolomite suggest that diagenetic solutions were dominated by meteoric water whereas delta sup 13 c values indicate that diageneticmore fluids were buffered by osagean carbonate rocks 54 refs 10 figs less

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

pervasive subsurface dolomitization of the nisku formation in central alberta abstract the nisku formation in the subsurface of central alberta canada contains pervasive dolomites that occur mainly as a replacement of reefal limestones the degree of pervasive dolomitization increases downdip along a structural homocline from about 25 to 100 vol and associated replacive anhydrites increase from about 5 to 20 vol pervasive dolomites occur as two types one type consists of almost non porous and impermeable mosaics of cloudy crystals that have diameters of 5 300 microns the other type has significant intercrystalline porosity and permeability and consists of cloudy and clear crystals ranging in size from 100 500 microns cathodoluminescence zonation is rare but modulated structures observed with tem are common both types of dolomite have strong xrd ordering refl ctions and are nearly stoichiometric sr concentrations 25 125 ppm increase and mn concentrations 20 400 ppm decrease upwards in several cores the boron contents of both dolomite types 20 50 ppm are enriched relative to other diagenetic phases 18 ppm the sr isotope ratios vary from 0 7089 0 7107 and are enriched relative to devonian and younger seawater oxygen and carbon isotope ratios cluster around 5 8 permil pdb and 2 0 permil pdb respectively and are similar to those of remnant calcites from the combination of stratigraphic petrographic petrophysical and geochemical data it is inferred that both types of matrix dolomite formed contemporaneously from the same fluids in a flow regime with predominantly upward fluid movement at temperatures between about 40 50 c and at burial depths of about 300 1 000 m most anhydrites formed originally as gypsum during the advanced stages and after matrix dolomitization and later recrystallized to the anhydrites now present based on all accumulated data and on mass balance calculations at least two types of subsurface flow could have caused pervasive dolomitization and gypsification anhydritization 1 expulsion of burial compaction water i e chemically modified seawater with or without additional contributions of m bearing formation waters from deeper parts of the basin e g middle devonian brines and 2 thermal convection of formation fluids originally underlying and or overlying the nisku

epigenetic dolomitization and the origin of xenotopic dolomite texture abstract xenotopic texture which is commonly observed in pre cenozoic rocks is defined here as a mosaic of anhedral crystals with irregular or curved intercrystalline boundaries and usually undulatory extinction xenotopic dolomite texture is similar in appearance to neomorphic limestone textures idiotopic dolomite texture euhedral to subhedral crystals with straight intercrystalline boundaries contrasts with xenotopic texture and is commonly observed in both cenozoic and more ancient dolomites texture may be controlled by the temperature at which crystals grow crystal growth theory predicts that at low temperature a smooth crystal surface is energetically favored and atoms are added to crystal faces layer by layer with dislocations acting as nucleation sites this results in faceted crystals and euhedral to subhedral crystal mosaics above a critical roughening temperature crt a rough surface is energetically favored surface nucleation does not require dislocations and atoms are randomly added to the crystal surface resulting in nonfaceted growth and an anhedral crystal mosaic it is hypothesized that a critical roughening temperature exists for dolomite above 50 c xenotopic dolomites are produced by dolomitization of limestone and or neomorphic recrystallization of dolomite at elevated temperature above the crt after burial idiotopic dolomites are produced below the crt by near surface processes and are occasionally produced above crt if growth inhibiting effects of the solution or impurities stabilize crystal faces calcite has a crt below 25 c and therefore develops anhedral crystal mosaics characteristic of neomorphic texture both at near surface and at elevated temperatures synthetic xenotopic dolomite was produced in the laboratory at 250 c and 300 c by dolomitization of aragonite and calcite skeletal fragments and by recrystallization neomorphism of nonstoichiometric cenozoic dolomites xenotopic dolomite resulted from the metamorphic recrystallization of the idiotopic hueco dolomite permian texas near the marble canyon intrusion at temperatures between 350 c and 600 c hydrothermal dolomitization of periclase calcite marble near the intrusion also resulted in a xenotopic texture xenotopic dolomite in the galena group ordovician wisconsin was produced by neomorphism of a preexisting dolomite during the emplacement of lead zinc sulfides at temperatures between 80 c and 227 c in the trenton limestone ordovician michig n xenotopic dolomite replaced limestone during the migration of hot 50 c fluids along fracture systems xenotopic dolomite was not observed in cenozoic dolomites that were subjected to temperatures near surface values only

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

burial diagenesis of middle ordovician carbonate buildups alabama usa documentation of the dominance of shallow burial conditions abstract middle ordovician carbonate buildups at two localities red mountain expressway rme tidwell hollow twh record evidence of burial diagenesis burial diagenetic phases include from oldest to youngest 1 blocky calcite 2 planar dolomite associated with stylolites 3 saddle dolomite in primary voids and late veins and 4 blocky calcite in late veins all blocky calcite cements post date ordovician meteoric cement based on cross cutting and superposition relationships and blocky calcite is the most common burial diagenetic phase present in the chickamauga buildups blocky calcite not in late veins formed from post ordovician meteoric water based on the multiple lines of evidence which include 1 variable 18o values 5 2 to 11 4 some of which are significantly more negative than values from ordovician meteoric cement 2 non radiogenic 87 sr 86 sr values 0 70847 to 0 70869 and 3 low fe and mn values near or below detection limit 400 ppm planar dolomite associated with stylolites has variable 18o values 1 4 to 6 1 e is ca rich non stoichiometric and has relatively low mn and fe values this phase is interpreted as forming during the mississippian or earliest pennsylvanian at a relatively shallow burial depth rare saddle dolomite has 880 5 9 to 7 2 0 this phase post dates planar dolomite and appears to record migration of basinal brines into the platform succession during the alleghenian orogeny late veins filled with saddle dolomite and blocky calcite have variable 18o compositions like blocky calcite 4 8 to 12 8 0 and likely formed under elevated temperature conditions if precipitation from 18o enriched burial brines is assumed

authigenic dolomite cementation in the upper cretaceous phosphate formation western desert egypt abstract the upper cretaceous phosphate formation in the western desert of egypt displays a characteristic facies association that includes marine phosphorites interbedded with black shales and glauconitic sandstones the upper part of the formation is characterized by the presence of thin phosphatic beds which are filled extensively with disordered and non stoichiometric mean mgco3 41 4 0 34 mol authigenic dolomite cement sem and the back scattered images of these coarse crystalline dolomite cements reveal that they display planar euhedral crystal boundaries polymodal crystal size distribution and variable inclusion pattern the relatively low and wide ranged 18o 0 87 to 4 15 vpdb values of the dolomite cements coupled with their depleted sr mean 187 26 ppm and high iron and manganese values mean 6851 554 ppm and 11599 229 ppm respectively invoke that they were formed from mixed hypo saline fluids within a mixing marine meteoric zone probably during a low stand period at the vicinity of the maastrichtian early tertiary unconformity meanwhile their negative 13c 1 31 to 3 56 vpdb values argue for a possible involvement of isotopically light carbon derived from degradation of organic matter during their precipitation

paleoecology of easter island evidence and uncertainties abstract the existence of palm dominated forests covering the island since the last glaciation and the recent deforestation by humans are paradigmatic in easter island s paleoecological reconstructions the timing and mode of the deforestation are controversial but there is general agreement that it actually occurred and it is often given as an example of a human induced environmental catastrophe with philosophical implications for the future of the whole planet to evaluate whether this is the only well supported hypothesis or if there might be other scenarios compatible with the paleoecological data this paper reviews all the available evidence on past vegetation changes on easter island the discussion is centered on three main points 1 the alleged nature and extension of the former forests 2 the taxonomic identity of the dominant palms and 3 the nature of the recent ecological changes leading to a treeless island the potential causes of the assumed deforestation are beyond the scope of this study concerning the first point palynological and anthracological results obtained so far are not only compatible with a forested island but also with other scenarios for example a mosaic vegetation pattern with forests restricted to sites with a high freshwater table gallery forests which are mostly around the permanent lakes and along the coasts with regard to palm identity some extant species have been proposed as potential candidates but the palms that dominated these forests seem to have become extinct and their identity remains unknown the existence of a sedimentary hiatus around the dates of forest decline complicates the picture and reinforces the possibility of climatic changes it is concluded that the hypothesis of a previously forested island has yet to be demonstrated therefore the recent ecological disaster human induced or not is still speculative several types of future studies are proposed for a better understanding of easter island s ecological history including modern analog studies from similar situations pollen dispersal modeling high resolution multi proxy studies along the cores obtained so far more coring campaigns in the search for older sediments and dna and isotopic analyses of plant remains for taxonomic identification purposes