permafrost tectonics and past and future regional climate change yukon and adjacent northwest territories late tertiary changes in the general circulation of the atmosphere regionally enhanced by uplift of the wrangell saint elias and coast mountains were sufficient to promote permafrost development in the western arctic permafrost developed in yukon territory and adjacent northwest territories during early pleistocene glacial periods after continued tectonic activity led to further modification of regional climate but degraded in the interglacials permafrost has been present in northern parts of the region since the illinoian glaciation but most ground ice in central yukon formed in the late wisconsinan the present interglacial is the only one with widespread evidence of permafrost which is maintained in the valleys of central and southern yukon by the saint elias mountains blocking continental penetration of maritime air from the gulf of alaska this reduces snow depth in winter while cold air drainage in the dissected terrain of the yukon plateaus enhances the near surface inversion leading t

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

geology and tectonics of japanese islands a review the key to understanding the geology of asia abstract the age of the major geological units in japan ranges from cambrian to quaternary precambrian basement is however expected as the provenance of by detrital clasts of conglomerate detrital zircons of metamorphic and sedimentary rocks and as metamorphic rocks intruded by 500 ma granites although rocks of paleozoic age are not widely distributed rocks and formations of late mesozoic to cenozoic can be found easily throughout japan rocks of jurassic age occur mainly in the jurassic accretionary complexes which comprise the backbone of the japanese archipelago the western part of japan is composed mainly of cretaceous to paleogene felsic volcanic and plutonic rocks and accretionary complexes the eastern part of the country is covered extensively by neogene sedimentary and volcanic rocks during the quaternary volcanoes erupted in various parts of japan and alluvial plains were formed along the coastlines of the japanese islands these geological units are divided by age and origin i e paleozoic continental margin paleozoic island arc paleozoic accretionary complexes mesozoic to paleogene accretionary complexes and cenozoic island arcs these are further subdivided into the following tectonic units e g hida oki unazuki hida gaien higo hitachi kurosegawa south kitakami nagato renge nedamo akiyoshi ultra tamba suo maizuru mino tamba chichibu chizu ryoke sanbagawa and shimanto belts the geological history of japan commenced with the breakup of the rodinia super continent at about 750 ma at about 500 ma the paleo pacific oceanic plate began to be subducted beneath the continental margin of the south china block since then proto japan has been located on the convergent margin of east asia for about 500 ma in this tectonic setting the most significant tectonic events recorded in the geology of japan are subduction accretion paired metamorphism arc volcanism back arc spreading and arc arc collision the major accretionary complexes in the japanese islands are of permian jurassic and cretaceous paleogene age these accretionary complexes became altered locally to low temperature and high pressure metamorphic or high temperature and low pressure metamorphic rocks medium pressure metamorphic rocks are limited to the unazuki and higo belts major plutonism occurred in paleozoic mesozoic and cenozoic time early paleozoic cambrian igneous activity is recorded as granites in the south kitakami belt late paleozoic igneous activity is recognized in the hida belt during cretaceous to paleogene time extensive igneous activity occurred in japan the youngest granite in japan is the takidani granite intruded at about 1 2 ma during cenozoic time the most important geologic events are back arc opening and arc arc collision the major back arc basins are the sea of japan and the shikoku and chishima basins arc arc collision occurred between the honshu and izu bonin arcs and the honshu and chishima arcs

global vegetation dynamics and latitudinal temperature gradients during the mid to late miocene 15 97 5 33 ma a 617 site palaeobotanical dataset for the mid to late miocene is presented this dataset is internally consistent and provides a comprehensive overview of vegetational change from 15 97 to 5 33 ma the palaeobotanical dataset has been translated into the biome4 classification scheme to enable direct comparison with climate model outputs the vegetation change throughout the langhian seravallian tortonian and messinian is discussed the data shows that the langhian which includes the end of the mid miocene climatic optimum represents a world significantly warmer than today the high northern latitudes were characterised by cool temperate forests the mid latitudes by warm temperate mixed forests the tropics by tropical evergreen broadleaf forests and antarctica by tundra shrub vegetation cool temperate mixed forest existed during the seravallian in the high northern latitudes a reduction in warm temperate mixed forests in the mid latitudes and a loss of tundra on antarctica was noted tortonian vegetation distribution indicates that further cooling had occurred since the seravallian the major changes in vegetation include the first evidence for cold taiga forest in the high northern latitudes and a further reduction of warm temperate mixed forests by the messinian this cooling trend had eliminated warm temperate mixed forests from the western usa and australia and had formed mid latitude deserts despite the cooling trend throughout the mid to late miocene the vegetation distribution of all four reconstructed stages reflect the vegetation of a world warmer than the pre industrial conditions the latitudinal distribution of bioclimatic zones suggests that the latitudinal temperature gradient for the langhian would have been significantly shallower than at present and has gradually but asymmetrically become more modern towards the end of the miocene first the southern hemisphere distribution of bioclimatic zones became more modern probably due to the climatic effects of a fully glaciated antarctica the northern hemisphere bioclimatic zone gradient continued to be shallower than modern throughout the miocene and slowly became more modern by the messinian

coupling patterns between para glacial and permafrost degradation responses in antarctica the recently deglaciated environments in maritime permafrost regions are usually affected by very active paraglacial processes elephant point is an ice free area of 1 16 km2 located in the sw of livingston island south shetland islands antarctica between 1956 2010 the retreat of the ice cap covering most part of this island has exposed 17 3 of the land surface in this peninsula two geomorphological units were identified in this new ice free area a moraine extending from the western to the eastern coastlines and a relatively flat proglacial surface the glacier in 1956 sat in contact with the northern slope of the moraine but its accelerated retreat in parallel to the warming trend recorded in the antarctic peninsula left these areas free of glacier ice subsequently the postglacial evolution was controlled by the relaxation phase typical of paraglacial systems the typology and intensity of geomorphological processes show a significantly different dynamics between the southern and northern slopes of the moraine this pattern is related to the different stage of paraglacial adjustment in both slopes in the southern side on coarser sediments pronival ramparts debris flows and alluvial fans are distributed with a low to moderate activity of slope processes in the northern side mass wasting processes are extremely active on fine grained unconsolidated sediments ice rich permafrost is being degraded by thermokarst processes landslides and mudflows transfer large amounts of sediments down slope the surface affected by retrogressive thaw slumps in the moraine has been quantified in 24 172 m2 which accounts for 9 6 of its surface the abundance of kettle lakes is also indicative of the degradation of the ground ice paraglacial processes are expected to continue in the moraine and proglacial area in the near future although their intensity and duration will depend on the magnitude and rate of future climate trends in the northern antarctic peninsula copyright 2015 john wiley sons ltd

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

triassic 40ar 39ar ages from the sakaigawa unit kii peninsula japan implications for possible merger of the central asian orogenic belt with large scale tectonic systems of the east asian margin the 218 4 0 4 228 8 0 9 and 231 9 0 7 ma 40ar 39ar laser probe pseudo plateau ages 2 49 63 39ar release of very low grade meta pelitic whole rocks from the sakaigawa unit date high p t metamorphism we argue that this event occurred in a subduction accretion complex not along the east asian continental margin but on the pacific side of the proto japan superterrane proto japan was a permian magmatic arc presently dispersed in the japanese islands which also contained older subduction accretion complexes the arc system was fringing but not yet part of the eurasian continent the middle to late triassic high p t tectono metamorphic event was partly coeval with proto japan s collision with proto eurasia along the southward extension of the central asian orogenic belt causing the main metamorphism in the hida oki terrane it is possible that this system continued via the cathaysia block china to indochina the late permian to middle triassic indosinian event might stem from docking of pacific derived terranes with southeast asia s continental margin the concept of the proto japan superterrane implies that the qinling dabie sulu suture zone joined the central asian orogenic belt to the east of the north china craton and did not continue to japan as commonly assumed

creep characteristics and process analyses of a thaw slump in the permafrost region of the qinghai tibet plateau china abstract a thaw slump in the permafrost region of the qinghai tibet plateau was monitored to investigate typical characteristics of creep positions and processes in combination with soil property analyses the results show that the thaw settlement exhibits a contraction effect in the horizontal direction because of uneven thaw settlement slope displacement of creep occurs only in the top 50 cm of the soil the gravimetric water content soil porosity and soil temperature are higher near the thaw slump in thaw seasons compared with the undisturbed soil however the shear strength is lower melting ground ice releases thaw water that converges along the slope and forms an overland flow at the front part of the gentle slope area and a ponding depression at the slope bottom the analyses of slope stability using the infinite slope model shows that the headwall of the slope is inevitably unstable and slides under saturated conditions whereas the gentle slope area and slope bottom with slight creep displacement are relatively stable the small retrogressive thaw slump is in an early development stage with increasing degree of thaw settlement and rate of erosion the headwall will become steeper and a thermokarst lake will form at the slope bottom

distribution and growth of thaw slumps in the richardson mountains peel plateau region northwestern canada abstract retrogressive thaw slumps are one of the most active geomorphic features in permafrost terrain this study investigated the distribution and growth of thaw slumps in the richardson mountains and peel plateau region northwestern canada using tasseled cap tc trend analysis of a landsat image stack based on the tc linear trend image more than 212 thaw slumps were identified in the study area of which 189 have been active since at least 1985 the surface area of the slumps ranges from 0 4 to 52 ha with 10 slumps exceeding 20 ha the thaw slumps in the region are all situated within the maximum westward extent of the laurentide ice sheet based on relations between frequency distribution of slumps and that of terrain factors in the landscape the slumps are more likely to occur on the ice rich hummocky rolling moraines at elevations of 300 350 m and 450 500 m and along east facing slopes slope aspects of 15 to 180 with gradients of 8 to 12 pixel level trend analysis of the tc greenness transformation in the landsat stack allowed calculating headwall retreat rates for 19 thaw slumps the 20 year average retreat rates 1990 2010 period for 19 slumps ranged from 7 2 to 26 7 m yr 1 with the largest slumps having higher retreat rates at the regional scale the 20 yr headwall retreat rates are mainly related to slope aspect with south and west facing slopes exhibiting higher retreat rates and large slumps appear to be generating feedbacks that allow them to maintain growth rates well above those of smaller slumps overall the findings presented in this study allow highlighting of key sensitive landscapes and ecosystems that may be impacted by the presence and growth of thaw slumps in one of the most rapidly warming region in the arctic

tectonic evolution of low grade metamorphosed rocks of the cretaceous shimanto accretionary complex central japan abstract we reconstructed the tectono metamorphic evolution of the low grade metamorphosed cretaceous shimanto accretionary complex in the kanto mountains central japan based on radiolarian fossils metamorphic temperatures derived from illite crystallinity analysis and timing of metamorphism based on illite k ar dating the accretionary age of the kobotoke group is turonian to maastrichtian 66 94 ma based on radiolarian fossils illite crystallinity data indicate metamorphic temperatures of approximately 300 c the illite k ar ages constrain the timing of metamorphism to the middle eocene around 40 ma combining our results and previous study we defined two types of low grade metamorphism within cretaceous shimanto accretionary complex of the kanto mountains the early metamorphism in excess of 300 c was related to the uplift of the sambagawa metamorphic rocks in turn associated with the subduction of the kula pacific ridge during the late cretaceous 65 75 ma this metamorphism is recorded in the otaki group within the northernmost part of the complex in the kanto mountains subsequent to the subduction of the kula pacific ridge a later period of metamorphism recorded in the kobotoke group is characterized by the thermal effects of the subduction of the young hot pacific plate during the middle eocene the effect of the early metamorphism occurred synchronously 500 km along the trench from southwest to central japan the later metamorphism occurred at 50 ma in kyushu and shikoku of southwest japan and at 40 ma in the kanto mountains of central japan this difference in the timing of metamorphism between southwest and central japan is explained by the northward migration of the young hot pacific plate

thaw lake expansion in a two dimensional coupled model of heat transfer thaw subsidence and mass movement 1 thaw lakes widespread in permafrost lowlands expand their basins by conduction of heat from warm lake water into adjacent permafrost subsidence of icy permafrost on thawing and movement of thawed sediment from lake margins into basins by diffusive and advective mass wasting we describe a cross sectional numerical model with thermal processes and mass wasting to test the model and provide an initial investigation of its utility the model is driven using historical daily temperatures and permafrost conditions for the northern seward peninsula alaska nsp thick syngenetic ice mean annual air temperature maat 6 c and yukon coastal plain ycp thin epigenetic ice maat 10 c in the model lakes develop dynamic equilibrium profiles that are independent of initial morphology these profiles migrate outward episodically and match the morphology of profiles from lakes that were measured at each site modeled nsp lakes expand more rapidly than ycp lakes 0 26 versus 0 10 m a 1 under respective modern climates when identical climates are imposed nsp lakes still grow more rapidly because their deeper basins and steeper bathymetric slopes move thawed insulating sediment away from the lake margin in sensitivity tests an increase of 3 c in maat causes 2 5 nsp and 1 6 ycp faster expansion of lakes an 8 c decrease essentially halts expansion for both sites consistent with paleostudies which attribute basins to postglacial warming in the model basins expand monotonically but lakes do not the 1 interannual variability of lake expansion is 0 51 nsp and 0 44 m a 1 ycp with single year rates of up to 8 m occurring because of instabilities from thermal mass movement coupling even under a stationary climate this variability is likely a minimum estimate compared to natural variability and suggests that long measurement time series of basins not lake surfaces would best detect thermokarst acceleration resulting from a climate change

global radiolarian zonation for the pliensbachian toarcian and aalenian jurassic radiolarians from 220 samples in queen charlotte islands b c williston lake b c east central oregon baja california sur southern spain austria slovenia turkey oman japan and argentina were studied in order to construct global zonation for the pliensbachian toarcian and aalenian stages well preserved faunas from continuous stratigraphic sections in queen charlotte islands provide the most detailed record for this time interval and all collections are tied to north american ammonite zones or assemblages collections from nearly all other areas lack independent dating except for early toarcian carbon isotope dating in slovenia and late aalenian ammonites in spain a database of 197 widely distributed updated taxonomic species was used to construct a unitary association ua zonation for the interval a global sequence of 41 uas was obtained for the top of the sinemurian to the base of the bajocian the first and the last uas represent the late sinemurian and the early bajocian respectively the remaining 39 uas were merged into nine zones four early pliensbachian one late pliensbachian one early toarcian one middle late toarcian and two aalenian according to prominent radiolarian faunal breaks and ammonite data the new zones are the canutus tipperi katroma clara zone latest sinemurian earliest pliensbachian zartus mostleri pseudoristola megaglobosa hsuum mulleri trillus elkhornensis and gigi fustis lantus sixi zones early pliensbachian eucyrtidiellum nagaiae praeparvicingula tlellensis zone late pliensbachian napora relica eucyrtidiellum disparile zone early toarcian elodium pessagnoi hexasaturnalis hexagonus zone middle and late toarcian higumastra transversa napora nipponica zone early aalenian and mirifusus proavus transhsuum hisuikyoense zone late aalenian these zones can be correlated worldwide and link previously established ua zonations for the hettangian sinemurian and the middle to upper jurassic the new zonation allows high resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of jurassic radiolarians

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

kurosegawa zone and its bearing on the development of the japanese islands abstract the kurosegawa zone in southwest japan is a 600 km long serpentinite melange in the chichibu terrains it runs generally e w but is slightly oblique to the subparallel arrangement of the ryoke sanbagawa and chichibu belts of southwest japan a variety of geological units occurs in the kurosegawa zone 1 1 granodiorite gneiss and amphibolite of ca 400 ma 2 2 siluro devonian formations 3 3 upper carboniferous to jurassic formations 4 4 upper jurassic to lower cretaceous formations 5 5 serpentinite and 6 6 low to medium grade metamorphic rocks of various baric types ages 220 320 360 and 420 ma by k ar the most widespread is a high pressure intermediate group of metamorphic rocks serpentinite is emplaced along the faults between and within the constituent units rocks of the kurosegawa zone represent a mature orogenic belt along a continental margin or an island arc its original site as constrained by paleomagnetism was near the equatorial area here 400 ma old paired metamorphism and related magmatism took place the island arc or microcontinent migrated northward to collide with the eurasia plate during late jurassic thus consuming the intervening ocean

deformation process and kinematics of melange in the early cretaceous accretionary complex of the mino tamba belt eastern southwest japan 1 the kanayama unit of the mesozoic mino tamba accretionary complex in eastern southwest japan is a thick melange unit composed mainly of abundant muddy matrix and variously sized clasts of chert hemipelagic siliceous mudstone and sandstone two episodes of deformation formed the melange fabrics the first involved fragmentation of sandstone layers in response to mud injections the second involved layer parallel noncoaxial shear that resulted in the mixing of pelagic to terrigenous clasts and the formation of s c like asymmetric fabrics with scaly foliation the s c fabrics exhibit a predominantly sinistral shear sense in plan view after fold and tilt corrections the restored slip motion inferred from the s c fabrics indicates a bulk top to the south shear combining the unit s terminal fossil age and radiometric age with a regional plate reconstruction model these data suggest that the kanayama melange formed along a decollement during oblique subduction of the izanagi plate in the early cretaceous

seasonal patterns of coupled flow in the active layer at three sites in northwest north america vertical arrays of temperature and electric potential probes were installed in the upper soil at sites along the mackenzie river valley and on the north slope of alaska time series were obtained at subdiurnal frequencies throughout the year in the active layer and upper permafrost if the data acquisition system is properly configured the time series can be used to infer soil physiochemical processes the electric potential develops primarily in response to soil water solute concentration gradients in the soil column and is a crude surrogate of the soil water electrolytic conductivity summer precipitation can cause rapid penetration of the thaw front when percolating rainwater warmed at the ground surface carries sensible heat downward to the thawing front rates of warming at depth occur significantly faster than those typical of conductive heat transfer in early winter as the freezing front penetrates downward toward the permafrost table ions are excluded from the ice and concentrated in the intermediate unfrozen zone nearly instantaneous warming of the active layer is triggered by spring snowmelt at happy valley in northern alaska temperatures at the 29 cm depth rise from 7 to 3 c in 1 h for several hours during this event the temperature at 29 cm is warmer than that at regions both above and below producing a strong thermal inversion time series of electric potential or a surrogate derived from electric potential suggest rapid transport of meltwater from the snowpack to depth probably through soil cracks serial events hasten active layer warming by 1 2 weeks

late palaeozoic to mesozoic structural evolution of the falkland islands a displaced segment of the cape fold belt the falkland islands lie on a displaced crustal block presently forming part of the south american plate the islands possess two roughly orthogonal structural grains the relative chronology of which is here unequivocally established for the first time d1 structures form a southerly verging permo triassic age fold belt striking e w to wnw ese which represents a displaced segment of the gondwanian orogenic belt the strike swing from e w to wnw ese is coincident with a decrease in deformation intensity toward the west on west falkland d1 folds are superimposed by the early mesozoic d2 ne sw trending hornby mountains anticline producing localized kilometre scale type i and iii fold interference patterns the hornby mountains anticline is interpreted to be the result of dextral transpressive reactivation of a pre existing ne sw basement fault if the falkland islands are rotated 180 the structure of the d1 fold belt and tectono sedimentary features of the permian age lafonian supergroup display a remarkable correlation with the structural style and tectonic evolution of the eastern cape fold belt of south africa our data therefore support a 180 tectonic rotation of the falkland islands and reaffirm their pre gondwana break up position adjacent to the southeast coast of south africa in such a reconstruction the falkland islands constrain the easterly extension and eventual lateral termination of the cape fold belt

age and implications of the forest bed falkland islands southwest atlantic ocean evidence from fossil pollen and spores diverse pollen and spore assemblages microfloras are preserved in organic clays and lignites associated with fossil tree remains in the forest bed at present these microfloras provide the only reliable basis for determining the age composition structure and affinity of the forest bed community the bed is suggested to be middle miocene to early pliocene age range oligocene early pliocene based on the time distribution of a number of rare pollen types and the present day ecology of their nearest living relatives in central southern america and the southwest pacific the wet forest community whose remains form the forest bed was a form of broadleaf gymnosperm temperate rainforest in which dacrydium lagarostrobos and podocarpus are likely to have formed an overstorey above a closed canopy dominated by nothofagus nothofagus spp the latter subgenus is now endemic to uniformly wet regions in southern south america whilst two of the tall gymnosperms dacrydium lagarostrobos are now endemic to the southwest pacific region an extinct probable shrub sized conifer podosporites microsaccatus appears to have formed the ground cover ferns and fern allies were very rare in contrast to most living nothofagus gymnosperm communities fossil pollen and spore types produced by uncommon subcanopy tree shrub and fern species potentially provide a means for more accurately dating the deposit once their time of first occurrence and extinction at subantarctic latitudes in the southwest atlantic region is established nearest living equivalents given in parentheses clavatipollenites cf glarius hedyosmum thymelaepollis sp ovidia type and cyatheacidites annulatus lophosoria this will require palynostratigraphic analysis of late palaeogene neogene sediments recovered from basins surrounding the falkland islands for example from dsdp site 329 drilled on the maurice ewing bank at the eastern margin of the falkland plateau

thermokarst lakes and ponds on mars in the very recent late amazonian past the history of water is fundamental to understanding the geological evolution of mars and to questions concerning the possible development of life on the red planet today mars is cold and dry it

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

accretion of the franciscan complex attending jurassic cretaceous geotectonic development of northern and central california scattered igneous activity marks the triassic margin of california but an andean volcanic plutonic arc began to form in the sierra nevada white inyo range and klamath mountains at ca 170 ma during underflow of the oceanic lithosphere this calc alkaline belt supplied volcanogenic erosional debris to the mariposa galice proximal overlap sequence by ca 165 160 ma transpression also generated high pressure low temperature basaltic eclogites garnet blueschists and amphibolites along the middle and late jurassic convergent plate junction at ca 170 155 ma most of these returned surfaceward as tectonic blocks only during the mid cretaceous the high grade metamafic metamorphosed mafic blocks that formed during construction of the emergent arc and derived mariposa galice strata predate the onset of franciscan trench deposition near the end of jurassic time the klamath salient evidently migrated 200 km westward an earliest cretaceous westward stepout of the convergent junction apparently formed directly offshore from the klamath imbricate orogen but to the south preexisting oceanic crust capped lithosphere was trapped landward as the coast range ophiolite andean arc detritus began to accumulate on this ophiolitic basement within the great valley forearc and outboard franciscan oceanic trench at ca 145 140 ma because earliest cretaceous relatively continuous great valley strata were deposited on the stable north american plate protected from both surface and subcrustal erosion forearc terrigenous sedimentation also signaled coeval deposition in the outboard trench 10 25 m y after middle and late jurassic initiation of the continental margin calc alkaline arc voluminous sedimentation and the accretion of franciscan and san joaquin sections of great valley rocks took place during mid and late cretaceous time after a flare up in igneous arc activity at 125 120 ma the youngest sierran granites have ca 85 ma ages reflecting extinction of the magmagenic zone beneath northern and central california and presumably reflecting subhorizontal oceanic plate underflow attending the laramide orogeny feebly zeolitized upper cretaceous and lower tertiary franciscan coastal belt rocks derived from the now inactive arc underwent only low pressure burial metamorphism reflecting shallow offloading and or large scale transpression they were not appreciably subducted although coastal belt units are members of the franciscan lithotectonic assemblage their origin contrasts with the rest of the subduction complex

headwall retreat of ground ice slumps banks island northwest territories the relationship between ice face ablation and headwall retreat is described for three ground ice slumps in the sand hills moraine southwest banks island retreat exceeds ablation by a geometric factor that depends on the slope of the ice and the gradient of the surrounding terrain amounts of retreat predicted from ice ablation calculations compare favourably with field measurements except at the start of thermokarst activity in the spring or when the ground ice remains covered by debris for long periods long term headwall retreat for slumps in southern banks island with different orientations and ice contents can be estimated using a model based on meteorological information the model predicts headwall recession of 11 m a for a ground ice slump facing south and 8 8 9 3 m a for one facing north with inputs of a 35 ice face a ground slope of 5 and a volumetric latent heat of 270 mj m3 these predictions are close to the maximum rates of retreat over a 10 year period as measured from air photographs

asymmetrical melange fabrics as possible indicators of the convergent direction of plates a case study from the shimanto belt of the akaishi mountains central japan abstract scaly foliated melanges in the upper maastrichtian lowest paleogene strata occurring in a zone several kilometers wide in the shimanto belt of the akaishi mountains central japan often exhibit composite planar fabrics on a mesoscopic scale with distinct monoclinic symmetry they are characterized by block in matrix fabrics including scaly foliations in mudstone matrices and asymmetric lensoidal and or ellipsoidal clasts of sandstone which were generated by extension parallel to the layers these fabrics are geometrically very similar to those of foliated fault related rocks another remarkable fabric is the imbricated stacks of lensoidal sandstone clasts forming mesoscopic duplexes by layer parallel contraction the co existence of these extensional and contraction planar fabrics suggests that non coaxial deformation had considerably progressed and that strain distribution was heterogeneous during formation of the melange systematic analysis of attitudes of these melange fabrics in many outcrops indicates that the fabrics have a remarkably consistent preferred orientation suggesting that a south trending overthrust shear about 40 70 counterclockwise with respect to the trend of strata prevailed during melange formation this direction is fairly consistent with the relative plate motion deduced from the regional tectonic framework of this age which indicates the oblique subduction of the pacific plate relative to the eastern margin of the eurasian continent thus the melange fabrics with monoclinic symmetry probably reflect the relative motion of consuming plates and may become excellent geological indicators for determining the direction of convergence of plates during melange formation since data on melange fabrics are directly and easily available in the field

late pleistocene sediments and environmental change at plaza creek falkland islands south atlantic late pleistocene organic rich sediments exposed in coastal bluffs near the head of plaza creek east falkland have yielded conventional and ams 14c dates of between 36 and 28 ka bp and possess a pollen spectrum dominated by grasses indicating a vegetation assemblage similar to that of the present day although some sample dates are anomalous and contamination by non contemporaneous carbon cannot be ruled out entirely the age estimates are consistent with evidence and dates from antarctica south america and the amphi north atlantic for climate shifts to interstadial conditions at around that time the organic rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting grain size characteristics suggest that these sediments may have been emplaced by solifluction shallow translational landsliding and surface wash in at least five mass wasting episodes some of the mass wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka bp at san carlos east falkland and with periods of cirque and valley glaciation identified in the uplands of the falkland islands the similarity between late pleistocene interstadial holocene and present day pollen assemblages and the lack of vegetation change within these periods is characteristic of most cool temperate southern ocean islands and may reflect the lack of sensitivity of the vegetation to climate change and or a lack of climate variability for the time intervals covered 1998 john wiley sons ltd

climatic evolution of the southern ocean during the pliocene epoch from 4 8 to 2 6 million years ago abstract we studied the paleoclimatic history of the southern ocean during the pliocene before the intensification of northern hemisphere glaciation at 2 4 ma from isotopic and sedimentologic data from odp leg 114 sites subantarctic south atlantic relatively warm climatic conditions prevailed in the southern ocean during the early early pliocene between 4 6 and 4 2 ma as evidenced by benthic and planktonic 18 o values that were generally less than the holocene despite this warmth significant ice rafting episodes are recorded at several drill sites and piston core locations throughout the southern ocean this interval correlates with a eustatic highstand and represents a climatic optimum for the southern ocean when low and mid latitude species migrated into the antarctic and surface waters were warmer than at present although it is generally agreed that this interval was warm in the southern hemisphere divergent opinions exist as to whether this warming led to the partial decay or growth of the antarctic ice sheet a distinct mid pliocene cooling occurred between 3 5 and 3 2 ma as evidenced by an increase in 18 o values of planktonic and benthic foraminifers in hole 704a and by faunal changes indicative of progressive cooling of antarctic surface waters and development of biotic provinciality in the southern ocean during the late pliocene 3 25 2 6 ma planktonic and benthic 18 o values commonly exceeded those of the holocene and several distinct cooling and or ice volume events occurred during the late gauss chron most notably at 2 9 and 2 63 ma faunal studies suggest several northward advances of the polar front zone and expansion of sea ice in the antarctic during this period these events preceded the major climatic transition at 2 4 ma when the pfz moved to the north sea ice expanded in the antarctic and glaciation intensified in both hemispheres

fluid rich damage zone of an ancient out of sequence thrust kodiak islands alaska 1 the uganik thrust is a fossil out of sequence thrust fault which was active over a period of 3 ma during the early tertiary until activity ceased with the subduction of the kula farallon spreading ridge at 57 ma during this period the fault experienced at least 1 km of throw and developed a strongly asymmetric damage zone the brittle damage zone in the footwall of the fault acted as a conduit for fluid advection during the active faulting a similar asymmetrical footwall damage zone has been interpreted as a fluid conduit at the nobeoka thrust shimanto belt sw japan thermal indicators in the uppermost footwall give similar maximum paleotemperatures to those in the hanging wall 280 c while previous work elsewhere in the footwall formation suggests maximum burial temperatures of 240 c in this case similar to the irish canyon thrust in the franciscan accretionary complex the location of the thermal anomaly is spatially offset from the structural fault which caused it owing to thermal overprinting in the vicinity of the fault

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

stratigraphic isotopic and mineralogical evidence for an early holocene thaw unconformity at mayo yukon territory ice rich glaciolacustrine sediments near mayo yukon territory reveal a thaw unconformity in the form of truncated ice wedges and abrupt changes in cryotexture the unconformity has been radiocarbon dated at 8870 200 years bp which is within the holocene period of optimal climatic conditions in northern yukon and the mackenzie delta area reported by other workers analysis of the mineralogy of the sediments indicates that the material above the unconformity is enriched in minerals that are the products of a more intense weathering environment than those deeper in the profile oxygen isotope ratios of ground ice in the sediments suggest the presence of two genetically distinct ice units above and below the unconformity an average rate of upward permafrost growth in this area of 0 1 0 2 mm year 1 is calculated for the period since the climatic optimum

terrain controls on the occurrence of coastal retrogressive thaw slumps along the yukon coast canada retrogressive thaw slumps rtss are among the most active landforms in the arctic their number has increased significantly over the past decades while processes initiating discrete rtss are well identified the major terrain controls on the development of coastal rtss at a regional scale are not yet defined our research reveals the main geomorphic factors that determine the development of rtss along a 238 km segment of the yukon coast canada we 1 show the current extent of rtss 2 ascertain the factors controlling their activity and initiation and 3 explain the spatial differences in the density and areal coverage of rtss we mapped and classified 287 rtss using high resolution satellite images acquired in 2011 we highlighted the main terrain controls over their development using univariate regression trees model coastal geomorphology influenced both the activity and initiation of rtss active rtss and rtss initiated after 1972 occurred primarily on terrains with slope angles greater than 3 9 and 5 9 respectively the density and areal coverage of rtss were constrained by the volume and thickness of massive ice bodies differences in rates of coastal change along the coast did not affect the model we infer that rates of coastal change averaged over a 39 year period are unable to reflect the complex relationship between rtss and coastline dynamics we emphasize the need for large scale studies of rtss to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget

mesozoic break up of sw gondwana implications for regional hydrocarbon potential of the southern south atlantic abstract this work provides new palinspastic palaeofacies reconstructions of sw gondwana incorporating rotation of a falkland malvinas microplate we discuss the implications of this for the tectonic evolution of the southern south atlantic and hence for the regional hydrocarbon potential existing gondwana reconstructions display good fits of major continents but poorly constrained fits of microcontinents in most continental reconstructions the falkland malvinas plateau was assumed to be a rigid fragment of pre permian south american crust however it has been suggested on the basis of palaeomagnetic data that the falkland malvinas islands were rotated by 180 after 190 ma this rotation hypothesis has been successfully tested on the basis of devonian stratigraphy and palaeontology permian stratigraphy and sedimentology and late palaeozoic and early mesozoic structure making it unlikely that the plateau behaved as a rigid structure during breakup we have explored the consequences of accepting this hypothesis for the tectonic evolution of sw gondwana by compiling new palaeogeographic maps for the permian cretaceous of the southern atlantic area to achieve a realistic close fit we have devised a pre rift proxy for the ocean continent boundary for the south atlantic in order to produce the best fit it is necessary to subdivide south america into four plates the consequences of this are far reaching our work suggests that although sedimentary basins were initiated at different times three major tectonic phases can be recognised in regional terms these can be thought of as pre syn and post rift during the pre rift time until the late triassic the area was dominated by compressional tectonism and formed part of the gondwana foreland the falkland malvinas islands lay east of africa the falkland malvinas plateau was 33 shorter and patagonia was displaced east with respect to the rest of south america in part along the line of the gastre fault system potential source facies are dominantly post glacial black shales of late permian age deposited in lacustrine or hyposaline marine environments these rocks would also be an effective regional seal sandstones deposited in the late permian would be dominantly volcaniclastic with poor reservoir qualities triassic sandstones tend to be more mature there was significant extension from about 210 ma end triassic until the south atlantic opened at about 130 ma early cretaceous in the early syn rift phase extension was accompanied by strike slip faulting and block rotation later extension was accompanied by extrusion of large volumes of lava early opening of the south atlantic was oblique which created basins at high angle to the trend of the ocean on the argentine margin and resulted in microplate rotation in ne brazil intermittent physical barriers controlled deposition of upper jurassic cretaceous anoxic sediments during breakup some of these mudrock units are effective seals with likely regional extent during crustal reorganisation clastic sediments changed from a uniform volcaniclastic provenance to local derivation with variable reservoir quality in the late rift and early post rift phase continental extension changed from oblique to normal and basins developed parallel to the continental margins of the south atlantic this change coincides with the main rifting in the equatorial basins of brazil and the early impact of the santa helena plume it resulted in widespread development of unconformities the abandonment of the reconcavo tucano jatoba rift and the end of ne brazil plate rotation which remained attached to south america there was extensive deposition of evaporites concentrated in but not restricted to the area north of the rio grande rise walvis ridge widespread deposits can be used to define potential regional elements of hydrocarbon systems and to provide a framework for relating more local elements our main conclusion is that the regional hydrocarbon potential of the southern south atlantic has been constrained by the tectonic evolution

the falkland islands a key element in gondwana paleogeography stratigraphic and sedimentological fieldwork on the falkland islands confirms that they were originally part of south africa east and west falkland have contrasting geological and deformation histories and are separated by the falkland sound fault which marks a significant deformation edge to the cape fold belt the degree of structural deformation and metamorphism in west falkland is substantially less than that of east falkland adjustments to differential shortening between the two islands being reflected by structures developed along the falkland sound fault prior to fragmentation of gondwana the falkland platform and maurice ewing bank were positioned in the natal valley adjacent to the east coast of south africa this predrift reconstruction shows that the falkland islands have subsequently been rotated by 180 relative to south africa and complements recent paleomagnetic data there was a complete overlap of the maurice ewing bank and falkland platform to the exclusion of the falkland plateau basin which is a small oceanic basin formed during the jurassic fragmentation of gondwana extension in this basin was accommodated by movements along the aghulas falkland fracture zone and the gastre fault system predrift restoration of these faults shows that patagonia was positioned closer to both africa and antarctica the falkland plateau basin was an integral component of the west gondwana jurassic microplate system and provides an invaluable insight into the evolution of its western margin at some time prior to the main opening of the south atlantic the falkland platform was rotated clockwise by 120 against the agulhas falkland fracture zone such that the falkland islands were translated some 300 km to the south the driving force for this rotation is not known but could possibly have been initiated by periodic stress buildups in the falkland plateau basin as the gastre fault system within continental crust became unable to accommodate the continuous dextral shear in the agulhas falkland fracture zone the falkland islands represent an outboard extension of the eastern cape and are significant for understanding the paleogeography of both the cape and karoo supergroups east falkland is closely similar to south africa in its geology while west falkland shows significant contrasts with both the devonian and permian successions being more proximal in character but still demonstrate the eastward continuation of the cape and karoo basins

margin parallel translation in the western pacific paleomagnetic evidence from an allochthonous terrane in japan abstract a new paleomagnetic study illustrates latitudinal translation of ribbon shaped continental fragments along the western margin of the pacific ocean though tectonic translations have long been recognized as prominent features in the eastern pacific margin i e north american cordillera we present new quantitative evidence for similar margin parallel motion through large scale strike slip faulting in the western pacific margin the kurosegawa terrane in southwest japan is an attenuated tectonic sliver and considered to be allochthonous with respect to the main part of southwest japan late triassic and early cretaceous sedimentary rocks from the terrane yielded paleolatitudes of 4 n and 18 n respectively based on paleomagnetic data of the kurosegawa terrane and plate reconstructions of east asia we suggest that the terrane was the easternmost element of the south china block at least from the late triassic to the early cretaceous the terrane was then translated 1500 km northward from the continental margin to its present position associated with sinistral strike slip movement along the east asian continental margin in mid to late cretaceous times the average displacement rate is calculated to be 7 cm yr and is comparable to rates reported for the eastern pacific margin

mimosoideae leguminosae occurrences in the early miocene of patagonia argentina abstract among materials extracted from early miocene strata of the chenque formation patagonia argentina polyads of acacia pollenites myriosporites cookson mildenhall and polyadopollenites sp anadenanthera aff macrocarpa were discovered recent affinities with polyads of acacia subg phyllodinae and anadenanthera respectively exist the presence of the mimosoideae corroborates for the early miocene of patagonia the convergence of two types of floras which today inhabit two different warm temperate regions namely neotropical america and australia this discovery also enlarges the known paleogeographic distribution ranges of both taxa

equatorial pacific sea surface temperatures faunal patterns and carbonate burial during the pliocene abstract a high resolution record of radiolarian faunal abundances from the eastern equatorial pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical pacific climate processes during the pliocene these data provide a means to evaluate the sensitivity of the equatorial pacific to the onset of northern hemisphere glaciation around 2 8 2 5 ma to the closure of the isthmus of panama around 4 4 3 2 ma and to orogeny related weathering changes before 4 0 ma radiolarian faunal assemblages and sea surface temperature sst estimates indicate a gradual cooling from early to late pliocene but no significant changes occur near the onset of northern hemisphere glaciation records of carbonate and noncarbonate mass accumulation show a long term decrease from the miocene pliocene boundary to the upper pliocene greater carbonate burial in the early pliocene relative to the late pliocene parallels a gradual cooling from early to late pliocene and may reflect changes related to isthmus closure or widespread orogeny no significant time domain changes are seen in the eastern equatorial pacific that could be related to the onset of northern hemisphere glaciation evolutive spectral analyses of these equatorial pacific climate parameters indicate that variance in sst and seasonality commonly concentrate at frequencies not linearly related to orbital variations furthermore cross spectral comparisons with a high resolution benthic 18 o record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the pliocene given the high degree of chronostratigraphic control in these records these results suggest that milankovitch band surface ocean processes as well as carbonate burial in the equatorial pacific are decoupled from high latitude climate processes during the pliocene

raman spectrum of carbonaceous material a possible metamorphic grade indicator for low grade metamorphic rocks raman spectral analyses of carbonaceous material cm extracted from pelitic samples along two sections traversing the metamorphic belt of taiwan were carried out in the present study the results show similar spectral variations of cm with metamorphic grade as those documented in the literature however continuous sampling from zeolite facies through prehnite pumpellyite facies to greenschist facies metamorphic rocks in the present study does reveal some interesting features on the raman spectra of cm that were not noted before both the raman d disordered o ordered peak area i e integrated intensity ratio and the d o peak width i e full width at half maximum fwhm ratio of the cm decrease with progressive metamorphism but the most prominent change in the d o peak area ratio occurs in samples of lower greenschist facies metamorphic grade while the most significant decrease in the d o peak width ratio occurs in samples near the boundary of prehnite pumpellyite facies and greenschist facies this phenomenon is interpreted as a result of the decoupling of the changing rates of in plane crystallite size and degree of defects of cm with progressive metamorphism it is postulated that the raman spectrum of cm can serve as a metamorphic grade indicator to distinguish samples of prehnite pumpellyite facies metamorphic grade from those of greenschist facies metamorphic grade

on the nature and origin of muck deposits in the klondike area yukon territory organic rich muck deposits which blanket auriferous gravels in the klondike area yukon territory comprise two principal stratigraphic units i a silty late pleistocene deposit and ii holocene organics lying unconformably on the silt the deposits are found predominantly in valley bottoms and if undisturbed are normally perennially frozen field and laboratory investigations of particle size mineralogy and morphology as well as organic matter and sedimentary structures indicate that the silt is both primary massive and redeposited bedded loess by weight 87 medium and coarse silt and fine sand radiocarbon dates indicate that the loess was deposited during late wisconsinan mcconnell glaciation beginning after 27 000 14c years bp the loess was likely derived from the floodplain of the yukon river during periods of low flow turf in growth position and organic matter in the silt similar to that of loessal grasslands near kluane lake suggest a grassland environment for the area during

the late jurassic oblique collisional orogen of sw japan new structural data and synthesis the structural configuration of sw japan mainly reflects a late jurassic early cretaceous orogeny the region is divided into an inner belt and an outer belt on the japan sea and pacific ocean sides respectively by a strike slip fault the median tectonic line mtl both consist of a series of stacked nappes the inner belt is divided into a jurassic olistostrome known as the tanba zone and a hinterland area comprising continental triassic jurassic sediments the tanba zone is sliced into two units a lower one with late jurassic matrix and triassic early jurassic radiolarite olistoliths tectonically overthrust by an upper unit comprising an olistostrome with middle jurassic matrix and blocks which include late paleozoic limestone basic lava and radiolarite the tanba zone is overthrust by a paleozoic nappe complex derived from the hinterland the basal sole of the nappe corresponds to a peculiar unit called the ultra tanba zone in the chugoku area the hinterland is divided into an upper nappe the oga nappe formed by permo carboniferous limestone and permian clastic rocks and a lower one the sangun maizuru nappe formed by paleozoic high pressure hp metamorphics the sangun schists the permian maizuru olistostrome and the dismembered paleozoic yakuno ophiolites in the northern part of sw japan the tanba zone is in faulted contact with the circum hida and the hida zones the former is interpreted as the equivalent of the oga and sangun maizuru nappes of the chugoku domain crushed by post cretaceous tectonics the latter consists of paleozoic high temperature ht metamorphic rocks and late triassic early jurassic granite locally mylonitized and covered by early jurassic sandstone the outer belt is formed by a superficial nappe similar to the tanba zone thrust upon a deep domain characterized by a synmetamorphic ductile deformation the deep domain is divided into a lower unit the oboke unit formed by continental derived arenites and a green schist nappe consisting of oceanic sediments and resedimented ophiolites the green schist nappe overthrusts the oboke unit under synmetamorphic conditions with an eastward displacement the two belts are separated by the ryoke zone which corresponds to the southern part of the tanba zone affected by a cretaceous ht metamorphism and sharply cut by the mtl a geodynamic model is proposed for the jurassic orogeny of sw japan assuming that the evolution of the inner and outer belts are linked in the late triassic early jurassic sw japan is an active plate margin the upper plate or south china block consisted of the hinterland and the tanba belt a forearc basin the lower plate consisted of an oceanic area and the south japan continent the basic mechanism of the orogeny is ascribed to the oblique subduction and collision of the south japan continent

evolution of cenozoic seaways in the circum antarctic region abstract a complete circum antarctic seaway did not open until both the south tasman rise cleared the oates land coast of east antarctica and drake passage opened between the southern tip of south america and the northern end of the antarctic peninsula major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the south tasman rise and antarctica as very close to the eocene oligocene boundary with an unrestricted opening deeper than 2000 m dating from 32 ma timing of the opening of drake passage is more circumstantial because the exact motions of certain micro continental fragments are not known the motion of africa with respect to south america as well as the motion of east antarctica with respect to africa are well constrained for the cenozoic these major plate motions are used with the reasonable assumption of no cenozoic motion of the antarctic peninsula with respect to east antarctica to constrain the location of the antarctic peninsula with respect to the southern tip of south america for the critical period of late eocene to late oligocene uncertainty of motion of the south georgia and south orkney microcontinents and other possible continental fragments make an exact time for opening of drake passage difficult to ascertain even so the early oligocene position of the antarctic peninsula with respect to south america requires a through going deep water seaway to have been open at drake passage prior to 28 ma even given the unconstrained motion of various high standing crustal fragments in the scotia sea with reasonable assumptions concerning motion of the crustal fragments in the western and central scotia sea it is likely that drake passage or passage through powell basin was open to deep water circulation by 31 2 ma

distribution of carbon and nitrogen along hillslopes in three valleys on herschel island yukon territory canada abstract thermokarst results from the thawing of ice rich permafrost and alters the biogeochemical cycling in the arctic by reworking soil material and redistributing soil organic carbon soc and total nitrogen tn along uplands hillslopes and lowlands understanding the impact of this redistribution is key to better estimating the storage of soc in permafrost terrains however there are insufficient studies quantifying long term impacts of thaw processes on the distribution of soc and tn along hillslopes we address this issue by providing estimates of soc and tn stocks along the hillslopes of three valleys located on herschel island yukon canada and by discussing the impact of hillslope thermokarst on the variability of soc and tn stocks we found that the average soc and tn 0 100 cm stocks in the valleys were 26 4 8 9 kg c m 2 and 2 1 0 6 kg n m 2 we highlight the strong variability in the soils physical and geochemical properties within hillslope positions high soc stocks were found at the summits essentially due to burial of organic matter by cryoturbation and at the toeslopes due to impeded drainage which favored peat formation and soc accumulation the average carbon to nitrogen ratio in the valleys was 12 9 ranging from 9 7 to 18 9 and was significantly higher at the summits compared to the backslopes and footslopes p

relations between air and surface temperature in discontinuous permafrost terrain near mayo yukon territory the association of site characteristics with the n factor a ratio of air to ground surface temperature was investigated at five sites in the boreal forest near mayo yukon territory permafrost was in equilibrium with surface conditions at three sites was degrading at another and was absent from the fifth air and near surface ground temperatures were recorded by data loggers between september 2000 and april 2002 and mean daily temperatures were accumulated to calculate n factors for the freezing nf and thawing nt seasons air temperature did not vary between the sites so inter site differences in nf and nt were because of variations in surface temperature variations in nf between the sites over the two winters were primarily because of differences in snow depth but at sites with similar snow cover the surface temperatures were relatively high when the site was underlain by unfrozen ground during summer daily mean surface temperatures were initially less than air temperatures however once

late quaternary vegetation and climate change in the amazon basin based on a 50 000 year pollen record from the amazon fan odp site 932 hemipelagic sediments from the amazon deep sea fan odp site 932 5 12 7 n 47 1 8 w and continental shelf provide a 50 000 yr long pollen record of amazon basin vegetation the age model for hole 932a is constrained by eight magnetic remanence intensity features one paleomagnetic excursion and three ams14c dates alchornea melastomataceae myrtaceae and moraceae urticaceae are dominant taxa in the pollen record between 40 200 and 19 800 cal yr b p andean taxa such aspodocarpusandhedyosmum increase in abundance between 19 800 and 11 000 cal yr b p and prior to 40 200 cal yr b p the holocene pollen assemblage derived from amazon river and continental shelf sediments is dominated by secondary growth taxa such ascecropia climatic factors influencing the development of glacial and interglacial tropical vegetation are considered by comparing marine with terrestrial records of vegetation change this comparison shows that the amazon basin forests were not extensively replaced by savanna vegetation during the glacial period contradicting the refugia hypothesis

late miocene earliest pliocene glaciation in southern argentina implications for global ice sheet history abstract in south america at latitude 47 s till was deposited sometime between 7 m y and 4 6 m y ago at a time when the local climate was colder than today s during this same interval glaciers extended to sea level in southeast alaska and widespread cooling of the ocean surface in middle latitudes worldwide marine regression and change in the oxygen isotopic composition of ocean water occurred from the last three events major late miocene expansion of the antarctic ice sheet has been inferred on the assumption that the history of north atlantic ice rafting precludes the existence of northern hemisphere ice sheets until 3 m y ago this is disputed first because precipitation in antarctica would probably have decreased at temperatures below today s second because the antarctic ice sheet cannot expand appreciably until buildup of northern hemisphere ice sheets has lowered sea level third because virtually no late miocene sediments are present at the labrador sea dsdp sites that are critical to the reconstruction of north atlantic ice rafting history and fourth because the scale of late miocene glaciation in alaska is at least permissive for simultaneous buildup of ice at similar latitudes further east if global ice sheet volume at the end of the miocene was greater than it is today by an amount that would have lowered sea level by several tens of meters the excess ice did not accumulate in antarctica but in the northern hemisphere chiefly in north america away from the atlantic coast

miocene climate and vegetation changes in the cape peninsula south africa evidence from biogeochemistry and palynology organic material from the noordhoek area on the western margin of the cape peninsula south africa was obtained from a 50 m long drill core dominated by fluvio lacustrine siliciclastic sediments the aim of this study is to constrain fluctuations in climate and the decline of tropical vegetation elements along the southwestern coast and the cape peninsula of south africa during the late cenozoic phase when the benguela upwelling system was established the approach was to combine palynological biogeochemical tetraether lipids and stable isotope c n studies of the organic bearing record from the noordhoek area on the western margin of the cape peninsula bulk c and n isotope data of sediment organic matter point to a predominantly c3 higher plant source vegetation mean annual air temperature mat from the analyses of tetraether lipids mbt cbt index was compared with palynomorphs from partly unpublished data of a previously drilled core adjacent to the study site the palynomorphs are of subtropical affinities and suggest that an open riparian forest would have existed in the early to middle miocene of the southwestern coast of south africa together these data sources allow vegetation and climate reconstructions of subtropical conditions during the early to middle miocene which comprised fluctuating open riparian forest and swamp vegetation temperatures rose in the middle miocene and were higher than those of the present day

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

tectono stratigraphy and low grade metamorphism of late permian and early jurassic accretionary complexes within the kurosegawa belt southwest japan implications for mechanisms of crustal displacement within active continental margin abstract we characterize the tectono stratigraphic architecture and low grade metamorphism of the accretionary complex preserved in the kurosegawa belt of the kitagawa district in eastern shikoku southwest japan in order to understand its internal structure tectono metamorphic evolution and assessments of displacement of continental fragments within the complex we report the first ever documented occurrence of an early jurassic radiolarian assemblage within the accretionary complex of the kurosegawa belt that has been previously classified as the late permian accretionary complex thus providing a revised age interpretation for these rocks the accretionary complex is subdivided into four distinct tectono stratigraphic units late permian melange and phyllite units and early jurassic melange and sandstone units the stratigraphy of these four units is structurally repeated due to an e w striking steeply dipping regional fault we characterized low grade metamorphism of the accretionary complex via illite crystallinity and raman spectroscopy of carbonaceous material the estimated pattern of low grade metamorphism showed pronounced variability within the complex and revealed no discernible spatial trends the primary thermal structure in these rocks was overprinted by later tectonic events based on geological and thermal structure we conclude that continental fragments within the kurosegawa belt were structurally translated into both the late permian and early jurassic accretionary complexes which comprise a highly deformed zone affected by strike slip tectonics during the early cretaceous different models have been proposed to explain the initial structural evolution of the kurosegawa belt i e micro continent collision and klippe tectonic models even if we presuppose either model the available geological evidence requires a new interpretation whereby primary geological structures are overprinted and reconfigured by later tectonic events

gravel bearing radiolaria as tracers for erosional events a review of the status of recent research in sw japan and korea abstract the authors introduce a case study of research on the provenance of radiolaria bearing gravels and clasts of the monomictic chert pebble conglomerates in the lower cretaceous monobegawa group a paralic molasse in the outer zone of southwest japan reconstruction of oceanic plate stratigraphy from gravels and clasts in monomictic chert pebble conglomerates based on their lithology and radiolarian ages is possible and effective for the provenance research in the case of the monobegawa group a review of provenance studies of radiolaria bearing gravels in mesozoic orogenic sediments in sw japan and korea is included the paper concludes with the discussion of the erosional events of the jurassic and pre jurassic accretionary complexes in sw japan with reference to the late mesozoic geological history in the eastern margin of asian continent

the thermal regime of a retrogressive thaw slump near mayo yukon territory the development of a retrogressive thaw slump near mayo yukon territory has been traced from initiation by bank erosion 1949 of the stewart river to stabilization in 1993 1994 the stabilized headwall of the slump is 450 m from the river and the slope of the slump floor is 3 a transect of the slump from the river to the stabilized headwall was drilled in july 1995 to determine the extent and rate of permafrost degradation in the slump floor thermistors were placed in access tubes to 12 m depth at five sites four near the transect and one in undisturbed terrain to determine the magnitude of thermal disturbance due to slump development data loggers at the sites recorded the ground temperature at 1 m depth for two years from august 1995 the annual mean ground temperatures measured by the data loggers varied between 1 2 and 1 8 c in the slump compared with 2 4 c in undisturbed ground indicating a disturbance of about 4 c due to slumping the depth of thaw in the slump floor is consistent wit

fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea yukon territory canada abstract patterns of coastal erosion in the arctic differ dramatically from those coasts in more temperate environments thick sea ice and shore fast ice limit wave based erosional processes to a brief open water season however despite this permafrost coasts containing massive ice ice wedges and ice bonded sediments tend to experience high rates of erosion these high rates of erosion reflect the combined thermal mechanical processes of thawing permafrost melting ground ice and wave action climate change in the arctic is expected to result in increased rates of coastal erosion due to warming permafrost increasing active layer depths and thermokarst rising sea levels reduction in sea ice extent and duration and increasing storm impacts with the most ice rich permafrost in the canadian arctic the southern beaufort sea coast between the tuktoyaktuk peninsula and the alaskan border is subject to high rates of erosion and retrogressive thaw slump activity under many climate change scenarios this area is also predicted to experience the greatest warming in the canadian arctic this paper presents results of a remote sensing study on the long term patterns of coastal erosion and retrogressive thaw slump activity for herschel island in the northern yukon territory using orthorectified airphotos from 1952 and 1970 and an ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools mean coastal retreat rates of 0 61 m yr and 0 45 m yr were calculated for the periods 1952 1970 and 1970 2000 respectively the highest coastal retreat rates are on north west facing shorelines which correspond to the main direction of storm related wave attack during the period 1970 2000 coastal retreat rates for south to south east facing shorelines displayed a distinct increase even though these are the most sheltered orientations however south to south east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south east exposures the number and the total area of retrogressive thaw slumps increased by 125 and 160 respectively between 1952 and 2000 as well the proportion of active retrogressive thaw slumps increased dramatically polycyclic retrogressive thaw slumps appear to develop in a periodic fashion related to retrogressive thaw slump stage and maximum inland extent

evidence of tertiary forest in the falkland islands islas malvinas recent examination of the sediments and microfossils of a wood bearing deposit in west falklands lat 51 21 s long 60 42 w indicates that it represents an in situ forest environment and not driftwood as originally assumed following its description in 1912 palynomorphs in the organic matrix are consistent with wood identifications and record a local palaeoenvironment of podocarp type forest with some nothofagus and tree ferns physical characteristics of the sediment matrix also indicate a terrestrial rather than coastal origin the immense contrast of this forest with the treeless oceanic heath of the falklands at the present time makes a quaternary date extremely unlikely despite the excellent preservation of micro and macrofossils in the context of present knowledge of the southern hemisphere palaeoclimate a date of deposition prior to antarctic cooling and the initiation of the circumpolar current is suggested palaeobotanical characteristics of the palynomorph assemblage also suggest pre late tertiary date

simulating the decadal to millennial scale dynamics of morphology and sequestered carbon mobilization of two thermokarst lakes in nw alaska 1 thermokarst lakes alter landscape topography and hydrology in widespread permafrost regions and mobilize significant permafrost carbon pools including releasing methane ch4 to the atmosphere despite this the dynamics of lake evolution permafrost thawing and carbon mobilization are not well known we present a 3 d numerical model of thermokarst lakes on organic rich yedoma permafrost terrains with surface water flow and pooling naturally defining lakes that deepen expand laterally and drain due to talik formation bank retreat and both gradual and catastrophic drainage we predict the 3 d pattern of microbial methane production within the talik over time as a first model test and calibration beginning with small protolakes we simulated 10 000 years of evolution of pear and claudi lakes two neighboring thermokarst features on the northern seward peninsula alaska simulated lakes approximated observed bathymetry but results are sensitive to initial topography and soil ice content local topography caused markedly different dynamics for the two lakes pear expanded rapidly across low relief topography fully drained multiple times and released little methane in later stages due to pleistocene carbon depletion by the first and largest lake generation claudi grew slowly and continuously across high relief topography forming high subaerial banks partial drainages left remnant horseshoe lakes that continued to expand into virgin yedoma mobilizing carbon at roughly the same rate irrespective of lake drainage the 2 discrepancy between simulated ch4 production and observed emission rates in claudi likely results from misestimation of hot spot ebullition labile carbon content ch4 co2 production ratio or microbial ch4 oxidation