detrital carbonate peaks on the labrador shelf a 13 7 ka template for freshwater forcing from the hudson strait outlet of the laurentide ice sheet into the subpolar gyre abstract the laurentide ice sheet lis was a large dynamic ice sheet in the early holocene the glacial events through hudson strait leading to its eventual demise are recorded in the well dated labrador shelf core md99 2236 from the cartwright saddle we develop a detailed history of the timing of ice sheet discharge events from the hudson strait outlet of the lis during the holocene using high resolution detrital carbonate ice rafted detritus ird 18o and sediment color data eight detrital carbonate peaks dcps associated with ird peaks and light oxygen isotope events punctuate the md99 2236 record between 11 5 and 8 0 ka we use the stratigraphy of the dcps developed from md99 2236 to select the appropriate r to calibrate the ages of recorded glacial events in hudson bay and hudson strait such that they match the dcps in md99 2236 we associate the eight dcps with h0 gold cove advance noble inlet advance initial retreat of the hudson strait ice stream hsis from hudson strait opening of the tyrrell sea and drainage of glacial lakes agassiz and ojibway the opening of foxe channel and retreat of glacial ice from foxe basin are represented by a shoulder in the carbonate data r of 350 years applied to the radiocarbon ages constraining glacial events h0 through the opening of the tyrell sea provided the best match with the md99 2236 dcps r values and ages from the literature are used for the younger events a very close age match was achieved between the 8 2 ka cold event in the greenland ice cores dcp7 8 15 ka bp and the drainage of glacial lakes agassiz and ojibway our stratigraphic comparison between the dcps in md99 2236 and the calibrated ages of hudson strait bay deglacial events shows that the retreat of the hsis the opening of the tyrell sea and the catastrophic drainage of glacial lakes agassiz and ojibway at 8 2 ka are separate events that have been combined in previous estimates of the timing of the 8 2 ka event from marine records sw iceland shelf core md99 2256 documents freshwater entrainment into the subpolar gyre from the hudson strait outlet via the labrador north atlantic and irminger currents the timing of freshwater release from the lis hudson strait outlet in md99 2236 matches evidence for freshwater forcing and lis icebergs carrying foreign minerals to the sw iceland shelf between 11 5 and 8 2 ka the congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the lis through hudson strait into the subpolar gyre and provides specific time periods when pulses of lis freshwater were present to influence climate

spatiotemporal evolution of paludification associated with autogenic and allogenic factors in the black spruce moss boreal forest of quebec canada paludification is the most common process of peatland formation in boreal regions in this study we investigated the autogenic e g topography and allogenic fire and climate factors triggering paludification in different geomorphological contexts glaciolacustrine silty clayey and fluvioglacial deposits within the quebec black spruce picea mariana moss boreal forest paleoecological analyses were conducted along three toposequences varying from a forest on mineral soil to forested and semi open peatlands plant macrofossil and charcoal analyses were performed on basal peat sections 50 cm and thick forest humus sphagnum in microdepressions paludification resulted in the decline of some coniferous species such as abies balsamea and pinus banksiana the paleoecological approach along toposequences allowed us to understand the spatiotemporal dynamics of paludification and its impacts on the vegetation dynamics over the holocene

electrical resistivity structure of the upper mantle beneath northeastern china implications for rheology and the mechanism of craton destruction abstract the north china craton ncc and central asian orogen belt caob in northeastern china experienced a range of tectonic events during the phanerozoic dominated by lithospheric thinning of the eastern ncc in the late mesozoic and cenozoic in order to better understand the tectonic evolution of the ncc and the caob new broadband and long period magnetotelluric data were collected along a north west to south east trending profile that extended from the caob across the yanshan belt the tanlu fault zone to the liaodong peninsula a two dimensional 2 d resistivity model was derived from inversion of the transverse electric mode transverse magnetic mode and vertical magnetic field data in the crust of the caob the resistivity model shows a northwest dipping low resistivity zone beneath the solonker suture that is identified as the suture zone formed by the collision between the siberian and north china cratons the upper mantle of the caob is characterized by moderate resistivity values 300 1000 m that are best explained by the presence of hydrogen dissolved in olivine the water concentration of the caob mantle is comparable to values reported for the asthenosphere and cratons that have been significantly hydrated the ncc upper mantle is generally lower in resistivity than the caob upper mantle and a zone of lower resistivity is observed in the upper mantle at the southeast end of the profile beneath the ncc superimposed on this southeast decrease in upper mantle resistivity three low resistivity zones were imaged 1 below the xilamulun fault 2 close to the north south gravity lineament and 3 between the northern yanshan belt and tanlu fault zone the low resistivities can be explained as regions of partial melts or fluids perhaps caused by asthenospheric upwelling together with seismic imaging results and geochemical data the resistivity model shows that the modification of the lithosphere associated with craton destruction has occurred in a spatially non uniform manner in the region of the ncc investigated in this study

ages and geodynamic settings of xilamulun mo cu metallogenic belt in the northern part of the north china craton abstract the xilamulun belt along the northern part of the north china craton is located in eastern segment of the central asian orogenic belt and has great economic potential for mo cu mineralization more than ten medium to large ore deposits have been discovered in this region in the recent years the major types of mineralization type include porphyry chehugou mo cu kulitou mo cu xiaodonggou mo and jiguanshan mo quartz vein nianzigou mo xinjing mo epithermal hongshanzi mo u and alteration assemblage liulingou mo the timing of mineralization was previously thought to be yanshanian 208 290 ma however indosinian 260 208 ma ages for intrusions and mineralization have been recognized in recent years based on geochronologic data and regional geological evidence it is suggested that the mineralization in the xilamulun belt was formed during multiple events the mineralization processes are related to a post collisional extension stage 258 210 ma with the generation of the porphyry molybdenum copper deposit a tectonic stress transformation from ns to ew 185 150 ma that gave rise to vein or porphyry molybdenum deposit and a lithospheric thinning stage 140 110 ma with porphyry molybdenum deposit

evidence of a strong paleoearthquake in 9 1 ka cal bp interpreted from mass transport deposits western quebec northeastern ontario canada this paper reviews and expands upon stratigraphic and chronologic evidence supporting the interpretation of a strong early postglacial paleoearthquake in western quebec northeastern ontario canada event horizon mapping at dasserat dufresnoy and duparquet lakes quebec coring at chassignolle and malartic lakes quebec analysis of varve exposures near both the twin falls and frederick house dams ontario and review of published and unpublished logs of varve exposures reveal that mass transport deposits formed in or are inferred to have formed in varve year vyr 1483 relative to the timiskaming varve series and about 9 1 ka cal bp are present at numerous locations within the study area the spatial extent of the vyr 1483 mass transport deposit signature covers at least 14 600 km2 and is best explained by shaking from a paleoearthquake the magnitude of the event is estimated to be a minimum of m 7 3 which is indicative of a strong paleoearthquake the vyr 1483 paleoearthquake is one of 11 events of m 5 occurring within a 425 varve year period between 9 4 and 8 95 ka cal bp and is likely part of a period of elevated early postglacial seismicity associated with rapid crustal unloading the absence of an equivalent signature within the younger portion of the glaciolacustrine or lacustrine deposits in local lakes implies that this paleoearthquake is the strongest to occur within the study area since about 9 1 ka cal bp the highly precise correlation of widely spaced mass transport and disturbed deposits provided by varves is essential to the paleoearthquake interpretation

geomechanical response to seasonal gas storage in depleted reservoirs a case study in the po river basin italy 1 underground gas storage ugs in depleted hydrocarbon reservoirs is a strategic practice to cope with the growing energy demand and occurs in many places in europe and north america in response to summer gas injection and winter gas withdrawal the reservoir expands and contracts essentially elastically as a major consequence of the fluid gas and water pore pressure fluctuations depending on a number of factors including the reservoir burial depth the difference between the largest and the smallest gas pore pressure and the geomechanical properties of the injected formation and the overburden the porous medium overlying the reservoir is subject to three dimensional deformation with the related cyclic motion of the land surface being both vertical and horizontal we present a methodology to evaluate the environmental impact of underground gas storage and sequestration from the geomechanical perspective particularly in relation to the ground surface displacements long term records of injected and removed gas volume and fluid pore pressure in the lombardia gas field northern italy are available together with multiyear detection of vertical and horizontal west east displacement of the land surface above the reservoir by an advanced permanent scatterer interferometric synthetic aperture radar psinsar analysis these data have been used to calibrate a 3 d fluid dynamic model and develop a 3 d transversally isotropic geomechanical model the latter has been successfully implemented and used to reproduce the vertical and horizontal cyclic displacements on the range of 8 10 mm and 6 8 mm respectively measured between 2003 and 2007 above the reservoir where a ugs program has been underway by stogit eni s p a since 1986 following a 5 year field production life because of the great economical interest to increase the working gas volume as much as possible the model addresses two ugs scenarios where the gas pore overpressure is pushed from the current 103 pi where pi is the gas pore pressure prior to the field development to 107 pi and 120 pi results of both scenarios show that there is a negligible impact on the ground surface with deformation gradients that remain well below the most restrictive admissible limits for the civil structures and infrastructures

the subglacial origin of the lake agassiz ojibway final outburst flood arc shaped scours sandwaves and channels on the hudson bay seafloor suggest that the catastrophic drainage of lake agassiz ojibway occurred as a subglacial flood beneath the laurentide ice sheet which covered northern north america

a geomechanical transversely isotropic model of the po river basin using psinsar derived horizontal displacement abstract hydrocarbon production co 2 subsurface sequestration and gas storage in exhausted reservoirs are a few anthropogenic activities involving the extraction or injection of fluids underground as a consequence the withdrawn injected formation undergoes an effective stress change that may induce deep deformations propagating to the ground level with possible fault re activations the geomechanical parameters needed to simulate and predict the above processes can also be indirectly inferred by interferometric synthetic apertur radar insar based techniques that are used to monitor the land surface displacements in the present study the insar measurements above two exhausted fields of the po river plain italy presently employed for seasonal gas storage are used to develop set up and calibrate a transversely isotropic geomechanical model of the porous medium it is shown that only assuming transverse isotropy allows for a satisfactory reproduction of both the vertical and horizontal displacements that cannot be simultaneously matched by a simpler isotropic model moreover similar parameters prove correct for both the reservoirs located about 30 km apart providing evidence of the regional range of the above model applicability

10be dating of former glacial lake naskaupi quebec labrador and timing of its discharges during the last deglaciation abstract the last deglaciation of the laurentide ice sheet in northern quebec and labrador led to the formation of several glacial lakes that drained into ungava bay and the nearby labrador sea assessing the potential impact of their drainage on ocean surface conditions and climate however is limited by the few existing age constraints on ice retreat and associated evolution of these lakes here we report 21 10be ages from shorelines and an outburst flood landform formed by lake naskaupi one of the largest glacial lakes in this region the results indicate that the lake drained from its full extent at 8300 300 a suggesting that it may have contributed to the freshwater forcing initiated by the drainage of lake agassiz ojibway that caused the 8 2 ka cold event additionally the results provide important constraints on the position of the ice margin of the labrador sector during its retreat across this region

evidence of late glacial paleoseismicity from submarine landslide deposits within lac dasserat northwestern quebec canada abstract an integrated seismo and chronostratigraphic investigation at lac dasserat northwestern quebec identified 74 separate failures within eight event horizons horizons e and b and h and g have strong or moderately strong multi landslide signatures respectively composed of 11 23 failures while horizons f d c and a have minor landslide signatures consisting of a single or pair of deposit s cores collected at six sites recovered glacial lake ojibway varve deposits that are interbedded with the event horizons the correlation of the varves to the regional timiskaming varve series allowed varve ages or ranges of varve ages to be determined for the event horizons horizons h g e and b are interpreted to be evidence of paleoearthquakes with differing levels of interpretative confidence based on the relative strength of the multi landslide signatures the correlation to other disturbed deposits of similar age in the region and the lack or possibility of alternative aseismic mechanisms the four interpreted paleoearthquakes occurred between 9770 200 and 8470 200 cal yr bp when glacial lake ojibway was impounded behind the laurentide ice sheet during deglaciation they probably represent an elevated period of seismicity at deglaciation that was driven by crustal unloading

a review and analysis of varve thickness records from glacial lake ojibway ontario and quebec canada abstract varve thickness records from glacial lake ojibway provide a detailed picture of ice margin dynamics and paleohydrology for the laurentide ice sheet during the early holocene the demise of lake ojibway occurred when an ice dam of the shrinking laurentide ice sheet failed perhaps releasing enough freshwater to impede atlantic meridional overturning circulation and precipitate the 8200 cal bp climatic cooling event previously published records and new information from lacustrine sediment cores are combined to reconstruct a varve record over 2100 years long between varves numbered 1 to 1500 average rates of ice margin retreat increased from 140 m y to as high as 400 m y beginning prior to varve year 1800 and lasting to around year 2000 ice readvanced along a front at least 300 km wide during an episode called the cochrane the total distance of the advance was at least 75 km and averaged around 200 m y during the advance a series of 50 anomalously thick varves were deposited the cause of which is uncertain a widespread unconformity occurred during the end of the cochrane advance which was followed at around varve year 2060 by the return of varves which thicken abruptly unlike previous varves these varves include ice rafted pellets of lake ojibway sediment these varves may have resulted from rapid melting and calving rather than a second advance and may relate to basin re filling following a lowstand there are no direct dates on the lake ojibway varves but a sudden increase in varve thickness at year 1528 is a regional stratigraphic marker that may have resulted from glacial sediment and meltwater including lake agassiz overflow diverted from routes to the lake superior basin into the lake ojibway basin dates from the lake superior basin suggest that the diversion of this water occurred at around 9040 cal bp applying this date to varve 1528 constrains the age of the lake ojibway varves numbered 1 to 2100 to between 10 570 and 8470 200 cal bp

seismic lg wave q tomography in and around northeast china 1 we investigate regional variations in the lg wave quality factor q in northeast china and its vicinity with a tomographic method digital seismic data recorded at 20 broadband stations from 125 regional events are used to extract lg wave spectra tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0 05 and 10 0 hz we simultaneously invert for the lg wave q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the q model and source function the best spatial resolution is approximately 1 1 in well covered areas for frequencies between 0 4 and 2 0 hz the lg q shows significant regional variations and an apparent relationship with regional geology we use a statistical method to investigate the regional variations of lg q and their frequency dependence the average q0 1 hz lg q in the entire investigated region is 414 sedimentary basins are usually characterized by lower average q0 values from 155 to 391 while volcanic mountain areas have relatively high average q0 values from 630 to 675 lg q generally increases with increasing frequency however the frequency dependence has complex nonlinear features on a double logarithmic scale indicating that the commonly adopted power law relationship may be oversimplified in a broad frequency band the frequency dependence varies in different geological areas with larger variations seen at lower frequencies

elusive isotopic properties of deglacial meltwater spikes into the north atlantic example of the final drainage of lake agassizthis article is one of a series of papers published in the special issue on the theme polar climate stability network the impact of the final drainage of lake agassiz some 8 4 ka ago on the atlantic meridional overturning circulation is still debated the lack of isotopic response in planktic foraminifer records at the outlet of the drainage channel constitutes a puzzling element in this debate to estimate the response of the 18o salinity relationship in ocean surface waters to drainage we use a core raised from southeast hudson bay to document 18o values of lake waters immediately prior to drainage valves of candona sp an ostracod from lacustrine varved sediments underlying marine clays yielded 18o values clustered around 20 5 versus vpdb vienna peedee belemnite assuming a lake bottom temperature of about 0 c an isotopic composition of 25 versus vsmow vienna standard mean ocean water is calculated for paleolake waters not unlike values reported for earlier stages of lake agassiz this value is only slightly more negative than those estimated for laurentide ice sheet lis meltwaters during the

insights on the events surrounding the final drainage of lake ojibway based on james bay stratigraphic sequences abstract deglaciation of the james bay region was highly dynamic with the occurrence of ice cochrane readvances into glacial lake ojibway around final deglaciation time which culminated with the drainage of ojibway waters into hudson bay and subsequent incursion of the tyrrell sea at 8 ka renewed interest on these events comes from the possible link between the drainage of the ice dammed lake agassiz ojibway and a major climate deterioration known as the 8 2 ka cooling event recent glaciological modeling suggests that this drainage may have occurred subglacially a mechanism that can accommodate more than one lake discharge as suggested by marine records the exact number and timing of drainage events as well as location of the lake discharge pathway s remain however largely unconstrained here we focus on the events that led to the drainage of lake ojibway by documenting late glacial sedimentary sequences located east of james bay our investigations indicate that the deglacial sequence consists of a readvance till extensive ojibway rhythmites and thick marine sediments the glaciolacustrine and marine units are separated by a 60 cm thick horizon composed of laminated silt beds containing rounded clay balls and disseminated clasts resulting from the abrupt drainage of the lake radiocarbon dating of marine fossils lying above the drainage horizon indicates that the glaciolacustrine episode ended around 8128 8282 cal yr bp micropaleontological analyses reveal that freshwater ostracods candona sp and marine microfossils foraminifers dinocysts occur together in the upper part of the ojibway sediments analysis of oxygen isotopes 18 o of ostracods and foraminifers originating from the same stratigraphic position show highly contrasting values that suggest possible subglacial exchanges between lake ojibway and tyrrell sea waters prior to the final drainage event the complexity of the deglacial events is further indicated by radiocarbon dating of marine shells retrieved from a cochrane till that suggests that the last ice readvance occurred almost simultaneously with the final lake discharge these results bring additional constraints on the drainage mechanism of the coalesced lake agassiz ojibway and indicate that the james bay region formed an important drainage pathway for meltwaters at the end of the last deglaciation

geomechanics of subsurface water withdrawal and injection land subsidence and uplift ground ruptures and induced seismicity are the principal geomechanic effects of groundwater withdrawal and injection the major environmental consequence of groundwater pumping is anthropogenic land subsidence the first observation concerning land settlement linked to subsurface processes was made in 1926 by the american geologists pratt and johnson who wrote that the cause of subsidence is to be found in the extensive extraction of fluid from beneath the affected area since then impressive progress has been made in terms of a recognizing the basic hydrologic and geomechanic principles underlying the occurrence b measuring aquifer compaction and ground displacements both vertical and horizontal c modeling and predicting the past and future event and d mitigating environmental impact through aquifer recharge and or surface water injection the first milestone in the theory of pumped aquifer consolidation was reached in 1923 by terzaghi who introduced the principle of effective intergranular stress in the early 1970s the emerging computer technology facilitated development of the first mathematical model of the subsidence of venice made by gambolati and freeze since then the comprehension measuring and simulation of the occurrence have improved dramatically more challenging today are the issues of ground ruptures and induced triggered seismicity which call for a shift from the classical continuum approach to discontinuous mechanics although well known for decades anthropogenic land subsidence is still threatening large urban centers and deltaic areas worldwide such as bangkok jakarta and mexico city at rates in the order of 10 cm yr

high resolution varve sequences record one major late glacial ice readvance and two drainage events in the eastern lake agassiz ojibway basin abstract lake ojibway developed at the southern laurentide ice sheet margin during the last deglaciation and covered vast expanses of northeastern ontario and northwestern quebec canada the late stage history of the lake is complex presumably marked by a coalescence with lake agassiz and by late glacial ice readvances into the basin shortly before its final drainage 8200 years ago however these events are poorly defined in the lake ojibway varve record here we present evidence for the occurrence of one major ice readvance and two distinct drainage events from two varve sequences in northwestern quebec the matagami section contains 231 varves that comprise an interval recording a late glacial cochrane ice readvance the la reine section spans 100 varves and the base of the sequence is characterized by a set of chaotic and coarse grained silty rhythmites that marks the first lake drainage these bottom rhythmites are overlain by a set of 65 thick varves which are in turn capped by a thick silt bed associated with the final drainage of lake ojibway varve thickness measurements allow the correlation of these sections with the main ojibway varve record that spans 2129 years in the region where varve 1 represents the start of sedimentation the matagami sequence covers varve years 1644 1874 and the onset of the cochrane readvance occurred in varve year 1817 the lower part of the la reine sequence below the bottom chaotic rhythmites was deposited between varve years 1843 1877 while the overlying set of thick varves is correlated to varve years 2065 2129 thus indicating a hiatus of 188 varves the distinct thick varves show strong compositional and stratigraphic similarities with the connaught sequence reported elsewhere in the basin and point to a connection with the late glacial cochrane ice dynamics which appear to have played an important role on the lake evolution these results indicate that the late stage history of lake ojibway was marked by the already known cochrane major ice readvance which was followed by two drainage events separated by at least 65 years consistent with north atlantic sediment records that document a two step drainage of lake agassiz ojibway

changes in the bathymetry and volume of glacial lake agassiz between 11 000 and 9300 14c yr b p abstract computer reconstructions of the bathymetry of the lake were used to quantify variations in the size and form of lake agassiz during its final two phases the nipigon and ojibway phases between about 9200 and 7700 14c yr b p ca 10 300 8400 cal yr b p new bathymetric models for four nipigon phase stages corresponding to the mccauleyville hillsboro burnside and the pas strandlines indicate that lake agassiz ranged between about 19 200 and 4600 km3 in volume and 254 000 and 151 000 km2 in areal extent at those times a bathymetric model of the last ponton stage of the lake corresponding to the period in which lake agassiz was combined with glacial lake ojbway to the east shows that lake agassiz ojibway was about 163 000 km3 in volume and 841 000 km2 in areal extent prior to the final release of lake waters into the tyrrell sea during the nipigon phase a number of catastrophic releases of water from lake agassiz occurred as more northerly lower outlets were made available by the retreating southern margin of the laurentide ice sheet we estimate that each of the four newly investigated nipigon phase releases involved water volumes of between 1600 and 2300 km3 the final release of lake agassiz waters into the tyrrell sea at about 7700 14c yr b p is estimated to have been about 163 000 km3 in volume

megaflooding associated with glacial lake agassiz abstract significant baseline and episodic megaflooding from glacial lake agassiz was routed to the south east and north coasts of north america over the lake s nearly 6000 year history the five phases of lake level change were controlled by which outlet was active which in turn was controlled by ice margin position and glacioisostatic adjustment the southern outlet is the oldest and best understood outlet while successively younger outlets are progressively less understood eastern drainage synchronous with the younger dryas chronozone had been assumed by most studies but a spillway to accommodate the 90 m drop in lake level is yet to be described with the south and east outlets unable to accommodate the necessary lake level drawdown the northwest outlet has become the default outlet with arctic ocean core data supporting it however extant terrestrial data from the continent only provides data for a large flood from the fort mcmurray area closer to the end of the younger dryas coinciding with the timing of the preboreal oscillation the challenge remains to find agreement between the marine and terrestrial records uncontroversial is the geomorphic and sedimentologic evidence for flooding into and out of the lake consisting of large spillways large boulders and in places giant current ripples composed of boulders flood discharge estimates into and out of the lake range from 0 04 to 1 sv with final subglacial drainage into the tyrell sea estimated at 5 sv sufficient to raise global sea level by 0 18 m and initiate the 8 2 ka stadial

late stage phases of glacial lake ojibway in the central abitibi region eastern canada abstract the decay of the laurentide ice sheet southern margin during the last deglaciation led to the development of lake ojibway that covered large expanses of northeastern ontario and northwestern quebec the history of ojibway lake phases is poorly detailed mainly because of the physical configuration of the lake basin and the dominance of fine grained glaciolacustrine sediments that prevent the formation of well developed and extensive sandy strandlines here we use a complex sequence of relict terraces carved in glaciolacustrine rhythmites to document the evolution of lake ojibway in northwestern quebec specifically lake levels were constrained by measuring the elevation of 154 raised wave cut scarps present in the eastern lake abitibi region results provide evidence for four distinct shorelines with elevations of 299 289 282 and 272 m 1 m at the latitude of la sarre the highest lake level documented appears to be linked to one of the two known kinojevis phases of lake ojibway while the three other lake levels project well below the main outlet system that controlled the elevation of the lake during the deglaciation the elevation uplift gradients and areal extent of these lower shorelines suggest that the two intermediate lake levels likely formed during late stages of the deglaciation following abrupt drawdowns of the lake s surface the fourth and lowest shoreline is associated with a postglacial lake that developed after the complete withdrawal of ojibway water from the region these low elevation shorelines bring new evidence for significant changes in the areal extent and depth of lake ojibway near the end of the deglaciation although the origin of these late stage phases remains unspecified the associated drawdowns likely implied routing events into newly deglaciated regions and or subglacial meltwater discharges into the north atlantic

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

synthetic aperture radar interferometry to measure earth s surface topography and its deformation synthetic aperture radar interferometry insar from earth orbiting spacecraft provides a new tool to map global topography and deformation of the earth s surface radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter scale accuracy these data sets aid in the analysis and interpretation of tectonic and volcanic landscapes if the earth s surface deformed between two radar image acquisitions a map of the surface dis placement with tens of meters resolution and subcentimeter accuracy can be con structed this review gives a basic overview of insar for earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of insar for mapping the topography and deformation of the earth

glacial lake agassiz the northwestern outlet and paleoflood valley morphology and sediment in the fort mcmurray region of alberta indicate that a catastrophic flood discharged down the lower clearwater and athabasca river valleys 9900 yr b p geomorphic and chronologic evidence suggests that glacial lake agassiz emerson phase was the probable water source as the flood incised a drainage divide located near the alberta saskatchewan border the level of glacial lake agassiz decreased by 46 m discharged 2 4 x 106 m3 s for at least 78 days and stabilized at 438 m above sea level in the lake wasekamio area at that time water entered the arctic ocean via glacial lake mcconnell and the mackenzie river rather than the gulf of mexico via the mississippi river as previously thought such a large influx of fresh water 8 6 km3 h into the arctic at the close of the last glaciation may have had an abrupt major influence on northern climate

basin scale compressibility of the northern adriatic by the radioactive marker technique the paper presents a constitutive model for the one dimensional vertical compressibility mv of the northern adriatic sedimentary basin based on in situ deformation measurements by the radioactive marker technique gas reservoir compaction and expansion occurring during the field production life and after its abandonment have been measured in three deep boreholes of the northern adriatic by fsmt formation subsidence monitoring tool and cmi compaction monitoring instrument developed by schlumberger and western atlas respectively the compressibility values as obtained by relating the shortening of the distance between several pairs of adjacent markers to the pore pressure decline experienced by the productive levels during the monitored time interval are statistically processed to reduce the influence of operational and instrumental errors the method of moving weighted averages is used over clustered depth intervals the compressibility thus derived is related to the in situ vertical effective stre

high resolution body wave tomography models of the upper mantle beneath eastern china and the adjacent areas 1 we present new 3 d tomographic models of vp vs and vp vsratio anomalies in the upper mantle beneath ec and adjacent areas this data was collected and interpreted with the goal of clarifying geodynamic processes that caused spatially variable event histories throughout eastern china ec during mesozoic to cenozoic time the tomographic images were constructed by inverting body wave travel times recorded at 1300 stations within the upgraded china national seismic network and 9 temporary arrays resolution tests for different depths and the featured velocity anomalies verify that the tomographic images capture the velocity heterogeneities in the upper mantle to depths of 700 km the salient features of vp vs and vp vsratio anomalies can be clearly identified these include strong multiscale heterogeneities occupying the upper mantle beneath ec and differences in the spatial scale of anomalies found beneath northern and southern areas of ec these features demonstrate a degree of spatial variability in the geodynamic evolution of ec we propose two mechanisms to explain these patterns first the western front of the subducted slab may have imparted greater horizontal compressional stress in areas where it impinged further eastward into ec these areas would experience stronger convection and an altered stress regime in the upper mantle creating significant thermal anomalies beneath the south china block scb relative to the eastern north china craton ncc second differing thermal states and viscosities for the eastern ncc and the cathaysia block cab resulted in differing responses to regional deformation the archean hinterland of the eastern ncc specifically has a colder thermal state and higher viscosity and therefore exhibits only small scale heterogeneities due to the effect of shear localization the neoproterozoic cab has a relatively warm thermal state with lower viscosity and thus deformed more continuously

a detailed lake level reconstruction shows evidence for two abrupt lake drawdowns in the late stage history of the eastern lake agassiz ojibway basin abstract glacial lake ojibway occupied large areas in northeastern ontario and northwestern quebec during the last deglaciation paleogeographic reconstructions depict lake ojibway and lake agassiz sharing a common water plane shortly before the final drainage of this lake 8200 years ago however the pre drainage surface elevation and extent of this large coalesced lake is based on scattered raised shorelines in the ojibway basin and poorly constrained geomorphological considerations which convey large uncertainties in lake level reconstructions and the attendant meltwater volume estimates used to assess the impact of this freshwater discharge here we address this issue by using 3098 elevation measurements of shorelines mapped on a lidar digital terrain model covering a key area in the ojibway basin our reconstruction is based on a gis model integrating the paleotopography which reinforces correlation of shorelines and the identification of lake levels the spatial distribution of shoreline elevation data points shows well defined clusters of shorelines aligned on distinct elevation ranges that delineate three widespread lake levels which are separated by two intervals with atypically low number of shorelines reflecting abrupt lake drawdowns this reconstruction considerably refines the sequence in the eastern ojibway basin and shows evidence for a two step drainage of lake agassiz ojibway the results provide constraints on the magnitude of the lake level drops and indicate that the pre drainage surface elevation of lake agassiz ojibway of earlier reconstructions was likely overestimated accordingly the configuration and structure of this lake stage should be re evaluated to that effect the new shoreline record provides an important framework for assessing late stage changes in lake levels across the agassiz ojibway basin which is a critical step towards the production of realistic models depicting the drainage of this large lake

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

land subsidence due to groundwater drawdown in shanghai introduction shanghai is located on the deltaic deposit of the yangtze river as illustrated in fig 1 fig 2 shows the main geological strata the total thickness of the quaternary deposit is about 300 m shanghai geology office 1976 1979 excessive pumping of the groundwater caused compression of the quaternary deposit and subsidence in shanghai although several countermeasures including recharge of the groundwater have been adopted to mitigate the rate of subsidence up to the present the recorded cumulative subsidence has been 2 3 m in the central area of shanghai this subsidence has caused a lot of social problems the immediate problem is the increase in the possibility of flooding from 1981 to 1994 rainfall flooding occurred 22 times at a rate of almost twice per year liu 2001 the possibility of tidal flooding also increased from 1956 the height of the dike along the coast line was increased four times with the crest elevation rising from 5 m to 6 8 m other problems caused by the land subsidence are damage to the sewerage system road buildings and subway tunnels etc in shanghai the monitoring of land subsidence started in 1921 the history of land subsidence in the urban area of shanghai can be divided into two periods namely a rapid subsidence period 1921 1965 and a controlled period 1965 present zhang han 2002 however there has been a tendency for the subsidence rate to increase after 1990 in this paper the mechanism of land subsidence due to excessive pumping of groundwater is discussed first then the measured field data are presented and the relationship between groundwater pumping and land subsidence is discussed

the lithosphere of north china craton from surface wave tomography abstract fundamental mode rayleigh wave group velocity dispersion data were used in a tomographic study to reconstruct the crust and upper mantle shear velocity structure in east asia this article expounds the features of lithosphere structure in different sub regions of north china and discusses their implications for the tectonic evolution and present tectonics of north china craton ncc the study revealed that strong earthquakes took place in the low velocity zones and along the boundaries between high and low velocities in the middle and lower crust the active nw trending zhangjiakou bohai seismic belt corresponds to a prominent low velocity zone in the crust and upper mantle lid in addition to the well known structural difference between western and eastern ncc we are able to resolve clearly the lithospheric features of sub regions in eastern ncc the southern north china basin and north yellow sea are characterized by a high velocity crust and upper mantle lid down to 70 80 km depth while the northern north china basin has a low velocity crust and the velocity below moho to about 130 km is rather uniform and low there is also a general trend of velocity decrease in the upper mantle from west to east the velocity images bear the imprints of subduction and collision that took place in the periphery of ncc since mesozoic and shed some light on the mechanism of mesozoic lithospheric thinning of eastern ncc

lakes of the huron basin their record of runoff from the laurentide ice sheet the 189 000 km2 hur n basin is central in the catchment area f the present q s r lanrentian great lakes that now drain via the st lawrence river to the north atlantic ocean during deglaciation from 21 7 5 ka bp and owing to the interactions of ice margin positions crustal rebound and regional topography this basin was much more widely connected hydrologi cally draining by various routes to the gulf of mexico and atlantic ocean and receiving over flows from lakes impounded north and west of the great lakes hudson bay drainage divide early ice marginal lakes formed by impoundment between the laurentide ice sheet and the southern margin of the basin during recessions to interstadial positions at 15 5 and 13 2 ka be in i each of these recessions lake drainage was initially southward to the mississippi river and gulf of mexico in the first recession drainage subsequently switched eastward along the ice margin to the north atlantic ocean in the second recession drainage continued southward through the michigan basin and later eastward via the ontario basin and mohawk river valley to the north atlantic ocean during the final retreat of ice in the huron basin from 13 to 10 ka be proglacial lake drainage switched twice from the michigan basin and the mississippi river system to the i north atlantic via the ontario basin and mohawk river valley finally diverting to the champlain sea in the st lawrence river valley at about 11 6 ka be new seismo and litbo stratigraphic information with ostracode data from the offshore lacustrine sediments were integrated with the traditional data of shorelines uplift histories of outlets and radio carbon dated shallow water evidence of transgressions and regressions to reconstruct the water level history and paleolimnological record for the northern huron basin for the 11 7 ka bp period negative excursions in the 8 80 isotopic composition of ostracodes and bivalves in southern lake michigan southwestern lake huron and eastern lake erie indicate an influx of water from ice marginal lake agassiz in central north america about 11 ka be a major decline in water levels of the huron basin after 10 5 ka bp followed the high level main lake algonquin phase as ice receded and drainage was established through the north bay area to ottawa river valley during the subsequent mattawa stanley phase the lake level history was dominated by fluctuations of tens of meters highstands of the earliest oscillations whose origin is not clear might be related to some of the well known post algonquin shorelines after 9 6 ka be it is suggested that large inflows from lake agassiz and hydraulic damming in downstream outlets were the likely cause of the lake mattawa highstands a lowstand at 9 3 9 1 ka bp occurred when these inflows were diverted or impeded by an ice advance in the nipigon basin area while undiluted meltwater continued to enter the huron basin assemblages and isotopic composition of the ostracode fauna indicate very dilute meltwater during the lowstands as late as 7 5 ka be and precipitation runoff with comparatively higher dissolved solids dur ing the highstands we speculate that the water composition of the lake mattawa highstands was dom inated by the agassiz inflows by that time much of lake agassiz was remote from ice marginal envi ronments and the inflows were drawn from surface water of the southern sector of the lake which was largely supplied by runoff and dissolved solids from the exposed land area of western canada major inflows apparently ended about 8 ka be but northern proglacial lakes apparently continued as melt water persisted in the huron basin until about 7 5 ka bp the cessation of major inflows initiated the final lowstand in the huron basin and the present hydrological regime of local runoff

evolution and paleohydrology of glacial lakes barlow and ojibway abstract the evolution of lakes barlow and ojibway two large ice contact glacial lakes that covered parts of northern ontario and western quebec from about 10 1 8 0 ka bp during the retreat of the laurentide ice sheet was reconstructed using deglaciation landforms ice flow indicators inscribed on bedrock 14 c dates of early postglacial vegetation accumulated in lake basins the distribution of mysis relicta a biological indicator of lacustrine submergence varve chronology and a detailed photogrammetric survey of the lake limit although the rate of ice retreat varied greatly throughout the basin the average rate in lake barlow ojibway was 450 m year rates of ice retreat deduced from varve chronology were assessed using predictable relationships between the lake limit the shoreline gradient and the rate of relative uplift over a 590 km long profile the gradient on the maximum elevation of the lake defines a parabola that is attributed to restrained rebound although in part it could be due to the position of the profile with respect to the overall uplift pattern generated by the ice sheet the life span of the lake determined from varve chronology 2110 years shows excellent agreement with the age difference obtained between that of marine shells overlying lake ojibway sediments at its northern end in hudson bay and the oldest radiocarbon ages on basal organics in lakes in the southern part of the barlow ojibway basin both lakes drained eastward through the ottawa river between 10 1 and 8 0 ka bp and the average yearly discharge to the north atlantic ocean during the last 1000 1500 years is estimated at about 946 km 3 at break up of the ice sheet in southern hudson bay at about 8 0 ka bp lake ojibway drained abruptly releasing an estimated 114 396 km 3 of freshwater into the tyrrell sea and raising sea level by about 30 cm

water sheet outburst floods from the laurentide ice sheet field evidence and a theoretical model support the concept that during wisconsinan glaciation subglacial water sheet outburst floods issued from a large subglacial lake located in the hudson bay ba

glacial lake agassiz a 5000 yr history of change and its relationship to the δ18o record of greenland lake agassiz was the largest lake in north america during the last period of deglaciation the lake extended over a total of 1 5 10 6 km 2 before it drained at ca 7 7 14 c ka 8 4 cal calendar ka new computer reconstructions controlled by beaches isostatic rebound data the margin of the laurentide ice sheet outlet elevations and a digital elevation model dem of modern topographic data show how variable the size and depth of this lake were during its 4000 14 c yr 5000 cal yr history abrupt reductions in lake level ranging from 8 to 110 m occurred on at least 18 occasions when new outlets were opened reducing the extent of the lake and sending large outbursts of water to the oceans three of the largest outbursts correlate closely in time with the start of large 18 o excursions in the isotopic records of the greenland ice cap suggesting that those freshwaters may have had an impact on thermohaline circulation and in turn on climate

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

groundwater pumping and land subsidence in the emilia romagna coastland italy modeling the past occurrence and the future trend 1 the emilia romagna coastland south of the po river delta italy has experienced a dramatic land settlement mainly due to the large groundwater withdrawal related to the local economic and tourist development started in the early 1950s although the use of surface water has reduced the settlement rate over the last three decades anthropogenic land subsidence still continues in a few kilometer wide coastal strip at a rate larger than the natural one the occurrence is reconstructed since 1946 with the aid of advanced finite element flow and poromechanical models implemented with a realistically detailed geology of the regional shallow multiaquifer system the models have been calibrated against the piezometric leveling and extensometer records observed over the last 50 years and a land subsidence prediction in 2016 is performed the results show that the extensive groundwater pumping that occurred in the past is most likely the main cause of the recent land settlement as well because of the delayed compaction of the clay aquitards comprised between the depleted aquifers however the available pumping data do not allow for a thorough understanding of the current local settlement process along the coastline which is the most vulnerable area of the emilia romagna region from an environmental viewpoint if the planned scenario of groundwater resource management will be implemented anthropogenic land subsidence is bound to become a marginal problem for the central and northern portion of the emilia romagna coastland

deglaciation ages and meltwater routing in the fort mcmurray region northeastern alberta and northwestern saskatchewan canada a field based reconstruction of the deglacial paleogeography in the fort mcmurray area permits 1 constraining the timing of meltwater routing to the arctic from the present hudson bay drainage basin and 2 minimum age estimates for ice margin positions that can be used to constrain ice sheet modeling results a downslope recession of the laurentide ice sheet resulted in a series of proglacial lakes forming between the ice margin and higher land to the southwest the paleogeography of these lakes is poorly constrained in part from the masking effect of boreal forest vegetation and map scale issues however recent space shuttle based dems increase the number and spatial extent of moraines identified within the study area resulting in a coherent pattern of ice margin retreat focused on the athabasca river valley an intensive lake coring program resulted in a minimum ten fold increase in the radiocarbon database used to limit moraine ages results indicate that deglaciation in this region was younger than previously reported and it is likely that the meltwater could not drain northward to the arctic ocean from any source southeast of the fort mcmurray area until approximately 9850 9660 14 cbp

intralithospheric mantle structures recorded continental subduction 1 we investigated the intralithospheric mantle ilm structures beneath the north china craton ncc by the seismic imaging with over 16 000 high quality receiver functions from 255 broadband stations these images were created for six profiles spanning different tectonic units in the ncc initially we inferred the crustal velocity model using an integrated receiver function imaging technique subsequently we performed a series of synthetic tests of common conversion point ccp stacking images to distinguish between the multiple waves generated by the crustal structure and the velocity discontinuities in the ilm the ilm structures were constructed by waveform inversion on the basis of these analyses our imaging results reveal 1 a homogenous lithospheric mantle in the western ncc 2 intermittent and juxtaposed velocity interfaces in the ilm beneath the southern ncc and 3 local high velocity and lower velocity volumes in the ilm beneath the eastern ncc in addition the lower crust beneath the southern ncc is thin and the moho dips northward which present evidence of the yangtze craton subduction beneath the ncc the imaged high velocity volumes in the ilm beneath the southern ncc were interpreted as a subduction remnant in the uppermost mantle which reveal a flat subduction channel resulting from the continent continent collision between the ncc and the yangtze craton the homogeneous ilm beneath a paleoproterozoic amalgamation zone in the ncc implies that the remnants of the lithosphere that were subducted before 1 8 ga might have sunk into the deeper mantle

on the importance of the heterogeneity assumption in the characterization of reservoir geomechanical properties the geomechanical analysis of a highly compartmentalized reservoir is performed to simulate the seafloor subsidence due to gas production the available observations over the hydrocarbon reservoir consist of bathymetric surveys carried out before and at the end of a 10 yr production life the main goal is the calibration of the reservoir compressibility cm that is the main geomechanical parameter controlling the surface response two conceptual models are considered in one i cm varies only with the depth and the vertical effective stress heterogeneity due to lithostratigraphic variability in another ii cm varies also in the horizontal plane that is it is spatially distributed within the reservoir stratigraphic units the latter hypothesis accounts for a possible partitioning of the reservoir due to the presence of sealing faults and thrusts that suggests the idea of a block heterogeneous system with the number of reservoir blocks equal to the number of uncertain parameters the method applied here relies on an ensemble based data assimilation da algorithm i e the ensemble smoother es which incorporates the information from the bathymetric measurements into the geomechanical model response to infer and reduce the uncertainty of the parameter cm the outcome from conceptual model i indicates that da is effective in reducing the cm uncertainty however the maximum settlement still remains underestimated while the areal extent of the subsidence bowl is overestimated we demonstrate that the selection of the heterogeneous conceptual model ii allows to reproduce much better the observations thus removing a clear bias of the model structure da allows significantly reducing the cm uncertainty in the five blocks out of the seven characterized by large volume and large pressure decline conversely the assimilation of land displacements only partially constrains the prior cm uncertainty in the reservoir blocks marginally contributing to the cumulative seafloor subsidence that is blocks with low pressure

lake agassiz final drainage event in the northwest north atlantic 1 the 8 2 ka climate event recorded in greenland ice cores is subject of debates with respect to causal linkage with a collapse of the atlantic meridional overturning due to the drainage of the late glacial lake agassiz here we present records from the nw north atlantic down current the flood discharge route showing that the 9 5 8 ka interval was marked by a succession of events the drainage itself corresponds to a twin layer of carbonate rich turbidites deposited within the calibrated 8 35 8 5 ka interval proxies of sea surface and deep current conditions do not indicate significant concomitant changes in the nw north atlantic the dataset however supports the concept that the 8 2 ka climate event may represent one of the manifestations of climate instability during an interval with major changes of land drainage in ne america due to the collapse of the laurentide ice sheet subsequent fast sea level rise and large scale reorganization of the north atlantic thermohaline circulation pattern

geochemistry and habitat of natural gases in po basin northern italy three types of natural gases can be distinguished in the po basin 1 bacterial gases dgr13cch4 60 ppt dgrdch4 180 to 200 ppt c2 0 2 which are found predominantly in pliocene pleistocene reservoirs 2 mixed gases dgr13cch4 60 to 50 ppt dgrdch4 180 to 200 ppt c2 0 2 to 5 which are predominantly in reservoirs of messinian upper miocene age but also in a few places in older and younger reservoirs 3 thermogenic gases dgr13c 50 ppt dgrd 200 to 150 ppt c2 5 which commonly are associated with oil and are produced predominantly from miocene and mesozoic reservoirs a quantitative assessment of gas in place for these three gas types is 1 80 2 10 and 3 10 respectively the areal distribution and amount of the three gas types are controlled strictly by geologic factors synsedimentary tectonics and turbidite sedimentation are the best conditions for the trapping of biogenic gas in the southeastern part of the area where 70 of the bacterial gas in place is produced here bacterially formed methane is produced from depths of up to 4 500 m 15 000 ft and is the deepest bacterial gas so far reported in the literature in the pedealpine homocline lower sedimentation rates and a weak deformation of pliocene pleistocene sediments prevented appreciable accumulations only 15 of the bacterial gas in the basin is produced in this area thermogenic gases are found in the vicinity of the apennines where strong tectonic movements have favored its migration from deeper mesozoic sources into tertiary reservoirs or into deep mesozoic carbonate reservoirs of the pedealpine homocline

ii cycle compressibility from satellite measurements knowledge of ground compressibility in unloading reloading conditions is of paramount importance in several geomechanical processes but its estimate is often affected by large uncertainties especially for deep rocks satellite measurements of the land motion can help improve this information the present study investigates the ground response due to underground gas storage activities as revealed by satellite interferometric measurements in three gas fields of the po river basin italy the ground proves to behave elastically moving upwards and downwards in response to gas injection and extraction respectively the accurate calibration of a detailed geomechanical transversely isotropic finite element model allows for an indirect estimate of the vertical ground compressibility in unloading reloading conditions which proves consistent with the results already available from the same basin assuming a hypo plastic constitutive model for the compressibility in virgin loading conditions the ratio betwee

aging of oil gas bearing sediments their compressibility and subsidence the in situ stiffness and apparent maximum preconsolidation stress of many soils and sediments appear to be higher than in the laboratory tests we seek to verify experimentally whether this also holds for deep marine sediments we also discuss an alternative explanation for this effect to the classical one implying the sample damage during coring we test numerically the explanation suggesting possible unaccounted changes in stiffness occurring in sediments in situ when subjected to aging or secondary compression for geological scale time periods results of aging tests on sandy and clayey sediments are presented involving secondary compression at the constant in situ stress level during which strain develops together with other changes in properties only two weeks of aging produced a notable increase in the apparent maximum preconsolidation stress and in the stiffness below it and above the in situ stress a framework for a mathematical model is proposed based on the supposition that during aging the sediment develops a secondary microstructure through reactions of local dissolution precipitation of less stable minerals

refining the glacial lake coverage of the southern laurentide ice margin using lidar dem based reconstructions the case of lake obedjiwan in south central quebec canada abstract the existence of former glacial lakes remains poorly documented in the remote regions of the canadian shield where the dense forest cover and poor access complicate classical mapping methods here we use a high resolution digital elevation model dem 1 m pixel based on lidar data to map quaternary deposits and landforms in the vicinity of the gouin reservoir in the laurentian highlands of quebec canada a total of 598 raised shorelines were identified providing new evidence for the presence of a large proglacial lake lake obedjiwan that formed in front of the northward retreating laurentide ice sheet margin during the last deglaciation a few kilometers east of the larger lake ojibway that covered extensive areas in northern ontario and quebec the elevation of shorelines outlines a tilted water plane that depicts the influence of the glacio isostatic adjustment across the basin with shorelines ranging from 409 m in the south to 439 m in the north the calculated uplift gradient of 0 78 m km indicates that the lake developed during the early stages of the deglaciation our reconstruction constrains the full areal extent and maximum elevation of the lake which covered an area of 1800 km2 and reached an elevation of 450 m it also indicates that lake obedjiwan developed independently from lake ojibway the lake surface elevation was controlled by an outlet located in the southeastern part of the basin where a topographic depression lying at an elevation of 390 m routed meltwater overflow southward through the saint maurice river and into the st lawrence river another important outlet is located in the northernmost part of the basin and ice retreat beyond this topographic depression 427 m caused the drawdown of the lake obedjiwan which drained westward into lake ojibway this discharge added around 19 km3 of meltwater an event that likely impacted the hydrological budget and sedimentology of lake ojibway the results suggest that other glacial lakes probably developed along the southern lis ice margin and that the approach developed in this study may contribute to the refinement of their areal coverage and improve paleogeographic reconstructions

cosmogenic 10 be dating of raised shorelines constrains the timing of lake levels in the eastern lake agassiz ojibway basin

complex responses of phototrophic communities to climate warming during the holocene of northeastern ontario canada historical changes in holocene climate in northeastern ontario were quantified using analyses of sedimentary pollen diatoms and pigments in a small boreal lake modern analog reconstructions of a

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

a century of land subsidence in ravenna italy over the last century the ravenna area has been affected by a widespread land subsidence process of both natural and anthropogenic origin which has become a matter of increasingly great concern land settlement initially of the order of a few mm year dramatically increased up to 110 mm year after world war ii primarily due to groundwater pumping and subordinately gas production from a number of deep on shore and off shore reservoirs spirit leveling was carried out in the area of the ravenna municipality by various authorities and agencies ever since the end of the nineteenth century using an increasingly refined network of benchmarks the available information spanning the time interval from 1897 to 2002 has been implemented and homogenized into a geographic information system gis measurements processed by kriging provide the pattern of the subsidence rates over the municipal territory during eight sub periods the reliability of data processing is discussed for both magnitude and areal distribution of the occurrence showing a pronounced nonlinear behavior in time as related to the major responsible factors cumulative land subsidence approaches almost 1 m over more than one third of the municipality area including the city and a significant fraction of the coastland with peaks larger than 1 5 m over a 10 km2 zone located between the historical center and the coastline most recent records show that at present the mainland appears to be substantially stable whereas some coastal areas are still subsiding at a rate of about 10 mm year with a significant threat to the environment and the infrastructures as well although to a lesser extent than in the past decades

land subsidence due to groundwater withdrawal in the northern beijing plain china abstract beijing is an international metropolis where over exploration of water resource makes land subsidence becoming more and more serious the related problems cannot be avoided in the coming years because of the giant increase of population the aims of this study are to quantify land subsidence over the period 2003 to 2010 grasp the evolution of the process and investigate the relation with the triggering factors in the northern area of the beijing plain various data including deep compaction from vertical multiple borehole extensometers land subsidence from persistent scatterer interferometry and leveling surveys groundwater levels hydrogeological setting from wellbores and landsat tm image were collected and effectively used to detect the spatial and temporal features of land subsidence and its possible relation with groundwater level changes compressible layer thickness and urban development results show that land subsidence is unevenly distributed and continuously increased from 2003 to 2010 the average loss of elevation over the monitoring period amounted to 92 5 mm with rates up to 52 mm y the distribution of the subsidence bowl is only partially consistent with that of the groundwater depression cone because of the variable thickness of the most compressible fine deposits in fact extensometers reveal that silty clay layers account for the larger contribution to land subsidence with the 15 m thick silty clay layer between 102 and 117 m depth accounting for about 25 of the total subsidence finally no clear correlation has been observed between the subsidence rates and the increase of the load on the land surface connected to the impressive urban development this study represents a first step toward the development of a physically based model of the subsidence occurrence to be used for planning remediation strategies in the northern beijing plain

postglacial paleoceanography of hudson bay stratigraphic microfaunal and palynological evidence cores containing representative sequences of postglacial sediments in northern and southern hudson bay were analyzed for their microfaunal foraminifers and ostracods and palynological dinocysts