late holocene activity of sherman and sheridan glaciers prince william sound alaska abstract two adjacent glaciers in the chugach mountains of south central alaska have markedly different histories on decadal to perhaps centennial timescales sheridan glacier has advanced and retreated hundreds of metres during the latest holocene its recent fluctuations have markedly altered local base level of sherman river which drains sherman glacier and flows into sheridan lake sheridan glacier advanced to its greatest extent during the little ice age raising base level of sherman river and inducing aggradation there of up to 17 m of sediment retreat of sheridan glacier formed a series of lakes that have coalesced as lower lake outlets have become available base level of sherman river has dropped resulting in the evacuation of substantial volumes of sediment from sherman river valley in about 2000 the terminus of sheridan glacier began to disintegrate retreat accelerated dramatically in 2010 by 2016 the glacier had retreated an average of 600 m from its 2010 terminus although some areas retreated up to 1 9 km and others did not retreat at all meanwhile sherman glacier continued a slow advance initiated by a rock avalanche that blanketed much of its ablation area in the 1964 alaska earthquake

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

late holocene glacial activity at bromley glacier cambria icefield northern british columbia coast mountains canada retreating and downwasting glaciers in the british columbia coast mountains are exposing the remains of forests buried during holocene age glacial advances despite recent progress in discerning th

recent and holocene climate change controls on vegetation and carbon accumulation in alaskan coastal muskegs abstract pollen spore macrofossil and carbon data from a peatland near cordova alaska reveal insights into the climate vegetation carbon interactions from the initiation of the holocene c the last 11 5 ka to the present 1 ka 1000 calibrated years before present where 0 1950 ce the holocene period is characterized by early deposition of gyttja in a pond environment with aquatics such as nuphar polysepalum and potamogeton and a significant regional presence of alnus crispa subsp sinuata carbon accumulation 50 g m 2 a was high for a short interval in the early holocene when sphagnum peat accumulated but was followed by a major decline to 13 g m 2 a from 7 to 3 7 ka when cyperaceae and ericads such as rhododendron formerly ledum groenlandicum expanded this shift to sedge growth is representative of many peatlands throughout the south central region of alaska and indicates a drier more evaporative environment with a large decline in carbon storage the subsequent return to sphagnum peat after 4 ka in the neoglacial represents a widespread shift to moister cooler conditions which favored a resurgence of ericads such as andromeda polifolia and increased carbon accumulation rate the sustained alnus expansion visible in the top 10 cm of the peat profile is correlative with glacial retreat and warming of the region in the last century and suggests this colonization will continue as temperature increases and ice melts

permeability control on transient slip weakening during gypsum dehydration implications for earthquakes in subduction zones a conflict has emerged from recent laboratory experiments regarding the question of whether or not dehydration reactions can promote unstable slip in subduction zones leading to earthquakes although reactions produce mechanical weakening due to pore fluid pressure increase this weakening has been associated with both stable and unstable slip here new results monitoring strength permeability pore fluid pressure reaction progress and microstructural evolution during dehydration reactions are presented to identify the conditions necessary for mechanical instability triaxial experiments are conducted using gypsum and a direct shear sample assembly with constant normal stress that allows the measurement of permeability during sliding tests are conducted with temperature ramp from 70 to 150 c and with different effective confining pressures 50 100 and 150 mpa and velocities 0 1 and 0 4 m s 1 results show that gypsum dehydration to bassanite induces transient stable slip weakening that is controlled by pore fluid pressure and permeability evolution at the onset of dehydration the low permeability promoted by pore compaction induces pore fluid pressure build up and stable slip weakening the increase of bassanite content during the reaction shows clear evidence of dehydration related with the development of r1 riedel shears and p foliation planes where bassanite is preferentially localized along these structures the continued production of bassanite which is stronger than gypsum provides a supporting framework for newly formed pores thus resulting in permeability increase pore fluid pressure drop and fault strength increase after dehydration reaction deformation is characterized by unstable slip on the fully dehydrated reaction product controlled by the transition from velocity strengthening to velocity weakening behaviour of bassanite at temperature above 140 c and the localization of deformation along narrow y shear planes this study highlights the generic conditions required to trigger instabilities during dehydration reactions it shows that pore fluid pressure build up during dehydration reactions associated with the localization of a velocity weakening reacting or dehydrated phase along shear planes is necessary for earthquake triggering

geochemical studies on permian manganese deposits in guichi eastern china implications for their origin and formative environments abstract permian manganese ore deposits are widely distributed in southwestern and eastern china guichi permian manganese district in southern anhui province central eastern china is currently the most important manganese metal producers in eastern china manganese ores mno 18 2 45 4 wt in guichi region occur in calcareous argillaceous and siliceous mn bearing sequence of the permian gufeng formation in contrast to mn bearing rocks the ores have higher mn fe p sr more than 1500 ppm and ni contents 480 ppm higher mn fe 5 and lan cen 2 values and lower co ni

late holocene glacial history of the copper river delta coastal south central alaska and controls on valley glacier fluctuations abstract fluctuations of four valley glaciers in coastal south central alaska are reconstructed for the past two millennia tree ring crossdates on 216 glacially killed stumps and logs provide the primary age control and are integrated with glacial stratigraphy ages of living trees on extant landforms and historic forefield photographs to constrain former ice margin positions sheridan glacier shows four distinct phases of advance in the 530s to c 640s in the first millennium a d and the 1240s to 1280s 1510s to 1700s and c 1810s to 1860s during the little ice age lia the latter two lia advances are also recorded on the forefields of nearby scott sherman and saddlebag glaciers comparison of the sheridan record with other two millennia long tree ring constrained valley glacier histories from south central alaska and switzerland shows the same four intervals of advance these expansions were coeval with decreases in insolation supporting solar irradiance as the primary pacemaker for centennial scale fluctuations of mid latitude valley glaciers prior to the 20th century volcanic aerosols coupled atmospheric oceanic systems and local glacier specific effects may be important to glacier fluctuations as supplemental forcing factors for causing decadal scale differences between regions and as a climatic filter affecting the magnitude of advances

elevation changes 1949 1995 of black rapids glacier alaska derived from a multi baseline insar dem and historical maps we have constructed a new digital elevation model dem of the 1995 surface of black rapids glacier a surge type glacier in the central alaska range using ers 1 2 repeat pass interferometry we isolated the topographic phase from three interferograms with contrasting perpendicular baselines numerous phase unwrapping errors caused by areas of poor coherence were corrected in all three interferograms using a novel iterative semi automated approach that capitalizes on the multi baseline nature of the dataset comparison of our dem with a 1949 us geological survey dem and with 1973 95 ground survey data shows the gradual return of black rapids glacier to a pre surge hypsometry following a surge in 1936 37 maximum elevation changes along the glacier center line in the ablation and accumulation areas are respectively 249 and 63 m 5 4 and 1 4 m a 1 maximum elevation changes of survey points at nearby locations are 4 9 m a 1 1975 84 and 0 5 ma 1 1975 85 center line thickening of 62 m between 1949 and 1995 1 4 m a 1 just above the loket tributary in the upper part of the ablation zone indicates dynamic thickening following the 1936 37 surge

origin of the early sinian minle manganese deposit hunan province china abstract the minle mn ores occur at the base of the early sinian minle formation black shales on the southeast limb of the motianling anticline these rhodochrosite ores are rich in organic carbon and fossil algae and formed in a bay or lagoon on a paleo continental margin with adjacent island barriers the salinity of water in the depositional basin was probably brackish the partly restricted ocean basin was characterized by low oxygen bottom waters and pore water ph values ranging from 9 to 11 and neutral to negative eh values which produced alkaline and reducing conditions suitable for precipitation of mnco 3 growth of blue algae played a role in concentrating metals especially mn changing the sedimentary environment photosynthesis prior to deposition and degradation of organic matter during diagenesis and enhancing the deposition of mnco 3 during diagenesis the mn was mainly derived from the continent with some portion supplied from submarine volcanic activity and supracrustal deep seated hydrothermal fluids

glacier change in western north america influences on hydrology geomorphic hazards and water quality the glaciers of western canada and the conterminous united states have dominantly retreated since the end of the little ice age lia in the nineteenth century although average rates of retreat varied from strong in the first half of the twentieth century with glaciers stabilizing or even advancing until 1980 and then resuming consistent recession this retreat has been accompanied by statistically detectable declines in late summer streamflow from glacier fed catchments over much of the study area although there is some geographical variation over recent decades glaciers in northwest bc and southwest yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat and glacier fed streams in that region have experienced increasing flows in many valleys glacier retreat has produced geomorphic hazards including outburst floods from moraine dammed lakes mass failures from oversteepened valley walls and debris flows generated on moraines in addition to these hydrologic and geomorphic changes evidence is presented that glacier retreat will result in higher stream temperatures possibly transient increases in suspended sediment fluxes and concentrations and changes in water chemistry with climate projected to continue warming over the twenty first century current trends in hydrology geomorphology and water quality should continue with a range of implications for water resources availability and management and hydroecology particularly for cool and cold water species such as salmonids copyright 2008 john wiley sons ltd

landsat based inventory of glaciers in western canada 1985 2005 abstract we report on a glacier inventory for the canadian cordillera south of 60 n across the two western provinces of british columbia and alberta containing 30 000 km2 of glacierized terrain our semi automated method extracted glacier extents from landsat thematic mapper tm scenes for 2005 and 2000 using a band ratio tm3 tm5 we compared these extents with glacier cover for the mid 1980s from high altitude aerial photography for british columbia and from landsat tm imagery for alberta a 25 m digital elevation model dem helped to identify debris covered ice and to split the glaciers into their respective drainage basins the estimated mapping errors are 3 4 and arise primarily from seasonal snow cover glaciers in british columbia and alberta respectively lost 10 8 3 8 and 25 4 4 1 of their area over the period 1985 2005 the region wide annual shrinkage rate of 0 55 a 1 is comparable to rates reported for other mountain ranges in the late twentieth century least glacierized mountain ranges with smaller glaciers lost the largest fraction of ice cover the highest relative ice loss in british columbia 24 0 4 6 occurred in the northern interior ranges while glaciers in the northern coast mountains declined least 7 7 3 4

nature and timing of quaternary glaciation in the himalayan tibetan orogen abstract much effort has been made in recent years to define the timing and extent of quaternary glaciation throughout the himalayan tibetan orogen these studies are challenging because of the logistical and political inaccessibility of the region and the inherent problems associated with the application of numerical dating techniques nevertheless the studies are providing abundant evidence for significant glacial advances throughout the last several glacial cycles and are beginning to accurately define the extent and timing of glaciation in selected regions studies are showing that himalayan tibetan glaciers in arid regions during the last glacial cycle reached their maximum extent early in the cycle and that global last glacial maximum glacier advances were significantly less extensive however along the more monsoonal influenced greater himalaya there is increasing evidence to suggest that glaciation was more extensive later in the last glacial cycle but this has yet to be fully assessed in addition the new studies are showing that throughout most himalayan tibetan regions significant glacier advances occurred during the lateglacial and early holocene with minor advances in some regions during the mid holocene the still relatively poor chronological control in the himalayan tibetan orogen however makes it difficult to construct correlations across the region and with regions elsewhere in the world this in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation across the himalayan tibetan orogen and to quantify paleoclimate change in this high altitude subtropical region the lateglacial and holocene glacial records however are particularly well preserved in several himalayan tibetan regions glacial successions such as these have the greatest potential to be examined in detail using newly developing numerical dating and geomorphic and sedimentologic methods to derive high resolution terrestrial records of glaciation that will help in paleoclimatic reconstruction for high altitude subtropical regions

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

ice volume and subglacial topography for western canadian glaciers from mass balance fields thinning rates and a bed stress model abstracta method is described to estimate the thickness of glacier ice using information derived from the measured ice extent surface topography surface mass balance and rate of thinning or thickening of the ice column shear stress beneath an ice column is assumed to be simply related to ice thickness and surface slope as for an inclined slab but this calculation is cast as a linear optimization problem so that a smoothness regularization can be applied assignment of bed stress is based on the flow law for ice and a mass balance calculation but must be preceded by delineation of the ice flow drainage basin validation of the method is accomplished by comparing thickness estimates to the known thickness generated by a numerical ice dynamics model once validated the method is used to estimate the subglacial topography for all glaciers in western canada that lie south of 60 n adding the present ice volume of each glacier gives the estimated total volume as 2320 km3 equivalent to 5 8 mm of sea leve

early and late holocene glacial fluctuations and tephrostratigraphy cabin lake alaska marked changes in sediment types deposited in cabin lake near cordova alaska represent environmental shifts during the early and late holocene including fluctuations in the terminal position of sheridan glacier cabin lake is situated to receive meltwater during periods when the outwash plain of the advancing sheridan glacier had aggraded a brief early holocene advance from 11 2 to 11 0 cal ka is represented by glacial rock flour near the base of the sediment core non glacial lake conditions were restored for about 1000 years before the water level in cabin lake lowered and the core site became a fen the fen indicates drier than present conditions leading up to the holocene thermal maximum an unconformity spanning 5400 years during the mid holocene is overlain by peat until 1110 ce when meltwater from sheridan glacier returned to the basin three intervals of an advanced sheridan glacier are recorded in the cabin lake sediments during the late holocene 1110 1180 1260 1540 and 1610 1780 ce the sedimentary sequence also contains the first five reported tephra deposits from the copper river delta region and their geochemical signatures suggest that the sources are the cook inlet volcanoes redoubt augustine and crater peak and possibly mt churchill in the wrangell volcanic field copyright 2013 john wiley sons ltd

tree ring dated little ice age histories of maritime glaciers from western prince william sound alaska tree ring studies at 13 glacier forefields in western prince william sound show little ice age glacial fluctuations were strongly synchronous on decadal timescales cross dated glacially overrun trees at eight sites indicate ice margins advanced in the early late twelfth through thirteenth centuries and middle seventeenth to early eighteenth centuries little ice age tree ring dates of 22 moraines at 13 glaciers show two main periods of stabilization the earlier of these in the first decades of the eighteenth century overlaps with the second period of glaciers overrunning trees and marks culmination of this middle little ice age expansion stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of little ice age glacial advance the detailed little ice age record from land terminating glaciers in western prince william sound is consistent on a timescale of decades with four other tree ring dated glacial histories from across the northern gulf of alaska this coastal northeastern pacific glacial record reveals the structure of the little ice age in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years

nanhuan manganese deposits within restricted basins of the southeastern yangtze platform china constraints from geological and geochemical evidence abstract the nanhuan manganese deposits in the southeastern yangtze platform occur in the black shale series in the lower part of the datangpo formation in order to constrain the genesis of the deposits a detailed study was undertaken that involved field observations major and trace element analyses organic carbon analyses and isotope analyses c o s the major findings are as follows 1 the ore bearing rock series morphology of the ore bodies and characteristics of ores in several deposits are similar the ore minerals are rhodochrosite and manganocalcite the gangue minerals are mainly quartz feldspar dolomite and illite minor apatite and bastnaesite occur in the manganese ores 2 the ores are enriched in ca and mg whereas they are depleted in si al k and ti compared to wall rocks the ores normalized to average post archean australian shale paas are enriched in co mo and sr the chondrite normalized rare earth element ree patterns for ores and wall rocks are between those of typical hydrogenous and hydrothermal type manganese deposits additionally the ores have positive ce anomalies with an average ce ce of 1 23 and positive eu anomalies with an average eu eu of 1 18 normalized to paas 3 the average content of organic carbon is 2 21 in the samples and the average organic carbon isotopic value 13cv pdb is 33 44 the average inorganic carbon isotopic value 13cv pdb of carbonates in gucheng is 3 07 while the values are similar in the other deposits with an average of 8 36 the oxygen isotopic compositions 18ov pdb are similar in different deposits with an average of 7 72 4 the sulfur isotopic values 34sv cdt of pyrite are very high and range from 37 9 to 62 6 average of 52 7 which suggests that the pyrite was formed in restricted basins where sulfate replenishment was limited the sulfate concentrations in the restricted basins were extremely low and enriched in 34s which resulted in the very high 34s values for the pyrite that formed in the manganese deposits therefore a terrigenous weathering origin for manganese can be excluded otherwise the sulfate would have been introduced into the basins together with terrigenous manganese which would have decreased the 34s values of pyrites the manganese which originated from hydrothermal processes was enriched in the restricted and anoxic basins and then it was oxidized to manganese oxyhydroxide in the overlying oxic waters whereby the products precipitated into the sediments the manganese oxyhydroxide in the sediment was then reduced to mn2 and released to the pore waters during the process of diagenesis some organic carbon was oxidized to co32 which made the depletion of 13c in manganese carbonates therefore we suggest that the nanhuan manganese deposits are hydrothermal sedimentary diagenetic type deposits

excellent source rocks discovered in the cryogenian interglacial deposits in south china geology geochemistry and hydrocarbon potential abstract the cryogenian 720 635 ma is characterized by the well known sturtian and marinoan glaciations which plays a key role in understanding remarkable climate and sea level changes and oxygenation events that occurred during the neoproterozoic era however less attention has been paid to the interglacial deposits recently we paid great attentions to the excellent hydrocarbon source rocks toc 2 in the cryogenian interglacial datangpo formation 663 4 ma 654 3 8 ma in south china which mainly consists of black shales with thin manganese interbeds making the interglacial interval a new focus to elucidate their characteristics and depositional environments petrological and geochemical studies were conducted on fresh rock samples collected from six sections gucheng sanlian xiaoxi gaodongyuan xiaochayuan yanglizhang in manganese mining areas at southeastern south china sedimentary reconstructions suggest a transition from restricted to open ocean environment during the deposition of the datangpo formation and this formation records variations from warm and humid to dry and cold climate black shales were deposited in its lowest member during the warm period and showed greatest thicknesses more than 20 m at depocenters microscopic observations of the black shale samples exhibited abundant benthic algae with great diversities indicating a gradual recovery of the ecosystem biomarker analyses further reveal that these algae combined with bacterial microorganisms prosperous in low salinity reducing environments were the dominant organic contributors to the source rocks which were inferred by low pristane pr to phytane ph ratio pr ph low gammacerane high tricyclic terpene and high c27 sterane contents trace element records combined with isotopic data suggest that the deposition of source rocks in datangpo formation were related to a burst in surface water productivity due to warm climate and better preservations resulted from anoxic waters within a stratified water column these findings indicate the cryogenian source rocks may provide a new potential field for future explorations of shale gas and deep oil and gas

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

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

the sedimentology and geomorphology of rock avalanche deposits on glaciers this article describes and compares the deposits of four large landslides on two glaciers in alaska using field mapping and remote sensing digital image analysis is used to compare the sedimentological characteristics of nearly 200 000 individual surface blocks deposited by three landslides at black rapids glacier in 2002 the debris sheets of one of the three landslides on black rapids glacier and a landslide emplaced on sherman glacier in 1964 are also investigated the three landslides on black rapids glacier have undergone little post depositional modification by glacier flow whereas the sherman glacier landslide has been transported supraglacially up to ca 1k m over the past 46 years the three debris sheets on black rapids glacier have coarse blocky rims at their distal edges and all four debris sheets have longitudinal flowbands characterized by differences in texture and produced by shearing within the moving debris elongated blocks are parallel to flow except at the perimeter of the debris sheets where they are aligned more perpendicular to flow blocks on the sherman glacier debris sheet have been reoriented by glacier flow the matrix shows no systematic differences with depth or distance from the source however it appears to become coarser over a time scale of decades due to weathering

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

genesis of the songhung gold polymetallic deposit in the hoechang district the democratic people s republic of korea constraints from geology petrochemistry and pb s c o isotope geochemistry abstract the songhung deposit is located in the southwestern part of the yangdok uplift zone yuz in the northern part of the pyongnam basin in the sino korean craton most of large and small scale gold deposits and occurrences were discovered and exploited in the western part of the yuz several tectonic events in this area are the key to understanding the gold and polymetallic mineralization in the sonhung deposit the yuz comprises the neoarchean rangnim metamorphic belt proterozoic and early paleozoic rocks in the central domain and granitoid intrusions of crustal and mantle derivation yangdok granitoid intrusions two extensive nne trending fault zones with mylonitized rocks are interpreted to represent detachment fault and two ne sw trending regional rift structures represent zones of subsidence e g the tokchon maengsan to the west the kowon to the east and the junghwa samdung subsidence to the south it is suggested that the yuz is a metamorphic core complex mcc similar to those in the north china craton ncc polymetallic mineralization in the songhung deposit is divided into early and late stages the early mineralization was formed during compressional deformation in the triassic accompanied by low grade metamorphism of the sedimentary host rocks variations in pb s c and o isotope ratios indicate that the ore forming fluids and metals were derived from the country rocks the au grade is insignificant in this style of mineralization the main gold polymetallic mineralization in the songhung deposit is related to tectonic extension of the region the pb s c and o isotope data indicate that these elements as well as ore forming fluids could be derived from both the granitic intrusion yangdok granitoid and the proterozoic and paleozoic country rocks

superheavy s isotopes from glacier associated sediments of the neoproterozoic of south china oceanic anoxia or sulfate limitation black shales and mn carbonates interbedded with glacial deposits from the neo proterozoic of southern china exhibit extremely heavy values of pyrite s isotopes that may reflect the peculiar environment of earth at this time 34 s averages 30 at tanganshan and 44 at xiangtan compared with typical values of 0 to 5 found in younger deposits furthermore there is no distinction between the shales and the mn carbonate ores in the neoproterozoic unlike the younger deposits which show much lighter 34 s in the shales than in the mn ores the spread is 25 most other chemical parameters are very similar to both the younger mn deposits and those from the paleoproterozoic the exception is the rare earth elements ree all neoproterozoic fe ores and most neoproterozoic mn ores lack the positive eu anomaly that characterizes archean and paleoproterozoic fe mn accumulations on the other hand neoproterozoic mn deposits have positive ce anomalies on north american shale composite nasc normalized plots in contrast to other mnco 3 ores the ree is also higher than in other mn deposits but lower than in modern deep sea crusts sulfide s values in all neoproterozoic shales tend to be exceptionally variable and to often show much heavier values than can be found in marine strata from the phanerozoic therefore the anomalous 34 s values we observed reflect peculiar conditions in the world oceans at this time rather than purely local effects times of enrichment of seawater sulfate in 34 s do not correspond to periods of glaciation so the likely cause of the s isotope patterns is not worldwide glaciation but a generally low level of dissolved sulfate s in the neoproterozoic oceans that allowed modest increases in the amounts of s removed as pyrite to drive down the oceanic s reservoir enough to produce strong rayleigh reservoir effects the abundance worldwide of sturtian age mn and fe deposits indicates an increase in fe flux to the oceans that would have been sufficient to depress so 4 2 levels severely and to result in residu al dissolved s extremely enriched in 34 s ree evidence indicates that most of this enhanced fe and mn flux came from diagenetic remobilization of detrital oxides

slight mass gain of karakoram glaciers in the early twenty first century the mass balance of hindu kush karakoram himalaya glaciers has been debated partly because of a severe lack of observations from the region an analysis of the regional mass balance of karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area

taku glacier alaska u s a on the move again active deformation of proglacial sediments taku glacier is one of the few glaciers in alaska u s a that has advanced over the last century 7 km since 1890 this advance slowed substantially during the past decade but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d 1 the advance produced dramatic proglacial sediment deformation up to 200 m in from of the terminus two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus the bulge nearest the terminus was 10 m high and 65 m wide the middle bulge 7 m high advanced at 15 cm d 1 and the distal bulge 3 m high and 50 m wide at 9 cm d 1 crenulations and prominent fractures developed in the overlying vegetation layer the frontal lobes of the bulges were steep and overlaid a shear zonc where sediments were being thrust up and over the ground surface ice proximal push moraines 1 10 m high formed along much of the 9 km wide terminus although deformation was minimal at some locations

bacterially mediated diagenetic origin for chert hosted manganese deposits in the franciscan complex california coast ranges numerous manganese deposits in the franciscan complex california occur as conformable lenses within bedded radiolarian chert argillite sequences that are in turn intercalated within thicker sections of sandstone and shale the field relations composition and petro graphic and isotopic characteristics indicate that the manganese was concentrated by diagenetic reconstitution of siliceous and hemipelagic sediment during burial the ore lenses are mn rich and fe poor assemblages consisting largely of rhodochrosite manganese silicates opal ct disordered cristobalite tridymite and quartz highly negative 13 c values for the carbonate carbon in rhodochrosite indicate that co 2 likely originated from oxidation of methane less negative values result from mixing of methanogenic carbon and co 2 derived from bacterial degradation of organic matter the 18 o values for the carbonate of rhodochrosite indicate temperatures of formation between 12 and 100 c the oxidation of methane prior to carbonate precipitation may have used the minor 0 4 0 5 mn and fe oxyhydroxides and oxides deposited with the sediment the mobilization of manganese from biogenic and terrigenous sources in the sediment column into discrete horizons and the fractioriation of manganese from iron reflect the presence of oxidation reduction boundaries and gradients in the sediment column fluids derived from compaction and silica dehydration reactions in the transformation of opal a x ray amorphous biogenic silica to quartz were involved in transportation of principal components sedimentary and geochemical attributes suggest that the deposits formed in a deep water environment in a zone of oceanic upwelling near a continental margin