the late paleozoic el imperial formation western argentina glacial to post glacial transition and stratigraphic correlations with arc related basins in southwestern gondwana abstract the el imperial formation of the san rafael basin records a succession of depositional environments during the latest mississippian to earliest permian that span before during and after the glaciation of west central argentina at the base of the formation a restricted marine environment is recorded in mudstone containing marl and rippled and deformed sandstone beds this unit or sequence 1 is incised by a deltaic facies association composed of cross bedded sandstone and conglomerate that form at least 5 stacked gilbert deltas the deltaic facies association grades upward into the glacially influenced facies association made up of stratified diamictite mudstone with dropstones and massive deformed sandstone indicating deposition by wet based tidewater glaciers that calved icebergs into the basin with contributions from mass movement processes the glacially influenced facies association is overlain by mudstone and horizontally laminated and cross bedded sandstone of the post glacial open marine facies association recording post glacial transgression followed by relative sea level fall the deltaic glacially influenced and post glacial open marine facies associations comprise sequence 2 sequence 2 is incised by conglomerate of the upper fluvial member or sequence 3 the strata of the el imperial formation are correlated to those of the other arc related basins of western argentina rio blanco calingasta uspallata and tepuel a bashkirian transgression and fluvial incision in the el imperial formation correlate with events in the rio blanco and calingasta uspallata basins to the north whereas glaciation continues to the south in the tepuel basin through the early permian the deviating stratigraphic record of the tepuel basin may be the result of its higher latitudinal position during the pennsylvanian early permian and higher altitude due to either tectonic convergence of the patagonian microplate or convergence along the panthalassan margin of southwestern gondwana

sedimentary record of a fluctuating ice margin from the pennsylvanian of western gondwana parana basin southern brazil abstract the parana basin is a key locality in the context of the late paleozoic ice age lpia because of its location east of the andean proto margin of gondwana and west of contiguous interior basins today found in western africa in this paper we document the sedimentary record associated with an ice margin that reached the eastern border of the parana basin during the pennsylvanian with the aim of interpreting the depositional environments and discussing paleogeographic implications the examined stratigraphic succession is divided in four stacked facies associations that record an upward transition from subglacial to glaciomarine environments deposition took place during deglaciation but was punctuated by minor readvances of the ice margin that deformed the sediment pile tillites well preserved landforms of subglacial erosion and glaciotectonic deformational structures indicate that the ice flowed to the north and northwest and that the ice margin did not advance far throughout the basin during the glacial maximum consequently time equivalent glacial deposits that crop out in other localities of eastern parana basin are better explained by assuming multiple smaller ice lobes instead of one single large glacier these ice lobes flowed from an ice cap covering uplifted lands now located in western namibia where glacial deposits are younger and occur confined within paleovalleys cut onto the precambrian basement this conclusion corroborates the idea of a topographically controlled ice spreading center in southwestern africa and does not support the view of a large polar ice sheet controlling deposition in the parana basin during the lpia

southern california permanent gps geodetic array continuous measurements of regional crustal deformation between the 1992 landers and 1994 northridge earthquakes the southern california permanent gps geodetic array pgga was established in 1990 across the pacific north america plate boundary to continuously monitor crustal deformation we describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes we compare displacement rates at four site locations with those reported by feigl et al 1993 which were derived from an independent set of global positioning system gps and very long baseline interferometry vlbi measurements collected over nearly a decade prior to the landers earthquake the velocity differences for three sites 65 100 km from the earthquake s epicenter are of order of 3 5 mm yr and are systematically coupled with the corresponding directions of coseismic displacement the fourth site 300 km from the epicenter shows no significant velocity difference these observations suggest large scale postseismic deformation with a relaxation time of at least 800 days the statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets two possible noise models fit the pgga data equally well as described in the companion paper by zhang et al this issue the pre landers data are too sparse and heterogeneous to derive a reliable noise model under a fractal white noise model for the pgga data we find that the velocity differences for all three sites are statistically different at the 99 significance level a white noise plus flicker noise model results in significance levels of only 94 43 and 88 additional investigations of the pre landers data and analysis of longer spans of pgga data could have an important effect on the significance of these results and will be addressed in future work

recent mass movement processes on the ebro continental slope nw mediterranean abstract mass movement is an important process controlling the sedimentary structure and growth patterns of the ebro continental slope during recent time at least quaternary about 37 of the slope surface is affected by mass movement features which are variable in distribution size and morphology the northern and central sectors are mainly affected by erosive canyons with gullies on their upper courses and massive and chaotic slump bodies on the middle and lower courses the southern sector is mainly affected by large scale slides 10 km and debris flow deposits in the three sectors the slope is also locally affected by small scale slides

on the origin of the itarare group basal nonconformity and its implications for the late paleozoic glaciation in the parana basin brazil abstract outcrop studies of the itarare group in the alfredo wagner area along the eastern margin of the parana basin in brazil reveal a partially exhumed nnw sse oriented glacial paleovalley the carboniferous rio do sul formation represents the basal interval of the glacially influenced itarare group and rests directly on precambrian basement rocks this nonconformity is thought to represent an areal scouring surface as indicated by the series of glacially carved linear depressions that were incised into the glaciated bedrock during glacial advances these large scale erosional landforms differ in their extent by orders of magnitude and include wide deep troughs as well as narrower shallower gouges glacial troughs and gouges usually display smaller scale subglacial erosion landforms such as polished and grooved striations on their walls and floors these indicate the nnw motion of a warm based grounded glacier in addition large scale erosional features represent local topographic lows within the major glacial paleovalley these local lows are large enough to contain part of the succeeding deglacial deposits which thin toward and onlap the wall of these depressions we grouped these deglacial deposits into six genetic facies associations fa 1 to 6 within three fining upward glacial cycles fa 1 is composed of black shale and represents an initial marine flooding event it can be correlated with the regionally widespread lontras shale fa 2 is composed of sandstones and mudstones associated with flood derived hyperpycnal flows and occasionally with surge type turbidites fa 3 is represented by plastered or injected matrix supported conglomerates emplaced as lodgment tills fa 4 comprises matrix and clast supported conglomerates sandstones and mudstones attributed to ice rafting and concentrated flows in grounding line fan facies this unit also contains ice keel dragging features carved into soft substrate fa 5 is composed of dropstone bearing black shale related to a second major marine flooding event within the paleovalley fa 6 comprises sandstones associated with channelized surge type turbidites forming the second turbidite system in the succession as these deposits are confined to a paleovalley we infer that sedimentation was influenced by topographically controlled ice streams instead of non confined widespread ice lobes as previously suggested reconstructing south america and southern africa in their positions during the lpia suggests that the glacial valleys then present in the namibia area may have extended further into the eastern margin of the parana basin in this scenario confined outlet glaciers would have flowed out from the namibian windhoek ice cap and terminated along the eastern margin of the parana basin

postglacial uplift neotectonics and seismicity in fennoscandia abstract fennoscandia has experienced major uplift in postglacial time which is assumed to reflect a glacial isostatic process connected to the melting of the last ice sheets extensive modelling of the isostatic movements show that the applied deglaciation and uplift model fit the observations well there are however areas with significant deviations between uplift measurements and regional model predictions the misfit between observations and the isostatic uplift modelling is interpreted here to reflect a tectonic component of the uplift the objective of the present investigation is to isolate this tectonic uplift component interestingly enough the areas found partly correspond to areas with pronounced seismic activity and the assumption that the postglacial rebound is responsible for much of the observed onshore seismicity is substantiated we conclude that there seems to be present day deformation along the shoreline of mid norway southern norway shoreline and mountain areas and along the swedish east coast with the centre northeast of the gulf of bothnia that cannot be explained by glacial isostasy not all of the deformations in these areas are necessarily co seismic the study suggests that such vertical deformations are small in magnitude and overprint the glacial rebound the deformations may be a consequence of the plio pleistocene erosional pattern which is of glacial origin

interlaminated ice proximal glacimarine sediments in muir inlet alaska muir inlet in glacier bay alaska is a glacial fjord receiving a tremendous volume of sediment annually the rate of sediment accumulation is greatest proximal to muir glacier about 9 m yr 1 and decreases away from the glacier the primary sediment sources are meltwater streams discharging at subglacial and ice marginal positions to form overflows interflows and underflows continuous turbidity currents overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge these effects produce cyclic deposits of a thin fine grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina this lamina couplet is termed a cyclopel underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems underflow deposits occur only in proximal positions 0 5 km from glacier face and are coarse grained reverse to normal graded and exhibit an increase in sorting and sand content up layer ice rafted debris identified as particles 177 m is ubiquitous though low 5 by weight and occurs as isolated particles frozen pellets or as lenses that in cores may have a lamina appearance proximally ice rafted debris is difficult to identify because proximal sediment is often as coarse grained deposited sediment may be reworked by tidal currents and sediment gravity flows depositional processes operating in muir inlet produce interlaminated sand silt clay that characterizes sediment proximal to a glacier and fines seaward to mud sediment is classified into one of three sediment types 1 1 type i sediment is very fine grained mean 8 65 7 17 o low in sand 0 1 11 2 and very poorly to poorly sorted it is the dominant sediment type in muir inlet and is transported by plumes and deposited by suspension settling 2 2 type ii sediment is fine to coarse grained mean 6 70 3 12 o low to high in sand 5 1 86 6 and very poorly to moderately sorted it represents reworked sediment proximal plume deposits or coarse grained laminae of cyclopels 3 3 type iii sediment is coarse grained mean 3 89 2 38 o high in sand 58 0 100 0 and poorly to well sorted it is deposited by sediment gravity flows or underflows

a depositional record of deglaciation in a paleofjord late carboniferous pennsylvanian of san juan province argentina the role of catastrophic sedimentation the combination of high sediment supply rates and ample accommodation within fjords provides high resolution records of deglaciation ancient fjord fills provide the potential for three dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process we describe the fill jejenes formation of a well exposed late carboniferous pennsylvanian glacial valley and its tributaries these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments the geometry of the valley and its tributaries is controlled by the underlying lower paleozoic lithologies a deep valley with steep sides exists where the bedrock is massive limestones and a broader shallower valley exists where the bedrock is generally a fine grained olistostrome the valleys are locally floored with diamictites including both in situ tillites and remobilized diamictites in the trunk valley these are locally overlain by a small shallow water delta the major part of the valley fill consists of a 150 m thick mudstone dominated succession probably generated by plumes of glacial outwash containing numerous dropstones that decrease in abundance down the fjord the mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys each of which has a distinctive clast suite related to the local subcrop the entire succession is overlain by 300 m of sandy turbidites of which the upper part includes large mass transport complexes intercalated within the succession in the trunk valley are structureless graded silty mudstones lacking dropstones but with abundant large wood fragments close to the steep western margin of the trunk valley each of these massive mudstones is underlain by a slump or debris flow locally containing meter scale blocks of ordovician limestone from the valley side we interpret these as a consequence of rockfalls from the steeper valley sides triggering debris flows on the subaqueous fjord slopes we suggest that large solitary waves were generated as the rockfalls entered the water traveling along the fjord and stripping vegetation from the shoreline large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds these deposits and other mass flow deposits within the succession emphasize the potential importance of catastrophic sedimentation within deglacial successions

thick and fast sedimentation in a pleistocene fiord lake of british columbia canada the central interior plateau of british columbia canada is dissected by numerous elongate glacially overdeepened lake basins akin to coastal fiords an air gun seismic reflection investigation 242 km of trackline of okanagan lake 120 km long 3 5 km wide shows that the pleistocene sediment fill is up to 792 m thick and that bedrock has been excavated by repeated pleistocene glacial erosion to nearly 650 m below sea level the depth of bedrock incision below the surrounding plateau is more than 2000 m exceeding that of the grand canyon in arizona the total volume of sediment infill within the narrow trenchlike basin is more than 90 km 3 and several lines of evidence suggest that this fill accumulated rapidly during a single phase of glaciolacustrine sedimentation during late wisconsin deglaciation of the region after 15 ka similar fiord lake basins up to 100 km long are common in the interior of british columbia if the data from okanagan are representative these basins may represent a major previously unrecognized component of the total glacial sediment flux to the ocean overdeepening below sea level and the focusing of large volumes of glacial sediment and meltwater into such basins are of considerable glaciologic significance and may record the fast unstable flow of ice streams during deglaciation of the cordilleran ice sheet

postseismic relaxation following the 1994 mw6 7 northridge earthquake southern california 1 we have reexamined the postearthquake deformation of a 65 km long linear array of 11 geodetic monuments extending north south across the rupture reverse slip on a blind thrust dipping 40 s 20 w associated with the 1994 mw6 7 northridge earthquake that array was surveyed frequently in the interval from 4 to 2650 days after the earthquake the velocity of each of the monuments over the interval 100 2650 days postearthquake appears to be constant moreover the profile of those velocities along the length of the array is very similar to a preearthquake velocity profile for a nearby similarly oriented array we take this to indicate that significant postseismic relaxation is evident only in the first 100 days postseismic and that the subsequent linear trend is typical of the interseismic interval the postseismic relaxation postseismic displacement less displacement that would have occurred at the preseismic velocity is found to be almost wholly parallel n70 w to the nearby 40 km san andreas fault with only negligible relaxation in the direction of coseismic slip n20 e on the northridge rupture we suggest that the n70 w relaxation is caused by aseismic right lateral slip at depth on the san andreas fault excess slip presumably triggered by the northridge rupture finally using the dieterich 1994 stress seismicity relation we show that return to the preseismic deformation rate within 100 days following the earthquake could be consistent with the cumulative number of m 2 5 earthquakes observed following the main shock

postglacial transgressions in late paleozoic basins of western argentina a record of glacioeustatic sea level rise the areas marginal to main glaciated centers are appropriate sites to distinguish the record of glacioeustatic sea level fluctuations the late paleozoic basins of western argentina show a marginal position with respect to the glaciated areas of eastern south america brazil in three of these basins tarija calingasta uspallata and central patagonian widespread glacial marine diamictites and their gravity reworked counterparts pass upward to open marine fine clastics mudstones shales and scarce fine sandstones with fossils of the levipustula zone of middle carboniferous late namurian westphalian age the presence of fine grained marine sequences capping the diamictitic deposits is interpreted as the sedimentary response to a glacioeustatic sea level rise expressed as a transgression in stratigraphic terms the glacioeustatic nature of this sea level rise is confirmed by the interbasinal facies based correlation of the transgressive episode and the paleolatitudinal positioning of this portion of gondwanaland during carboniferous times

facies characteristics of a proglacial turbiditic sand lobe at svalbard abstract a shallow marine turbiditic lobe inferred to be associated with an ice contact delta was deposited during the last glaciation weichselian at svalbard the norwegian arctic the postglacially raised sandy lobe is exposed in a 200 m long river section and exhibits six units that reflect an early phase of glaciomarine mud deposition followed by three episodes dominated by deposition from sandy turbidity currents the lobe is characterized by a complex pattern of turbidite filled erosional features from thin scour fills reflecting a highly mobile flow pattern to stacked chute fill deposits showing confined flow the sandy turbidites show rhythmic deposition of massive to graded laminae deposited from suspension alternating with faint laminae or ripple cross lamination deposited from tractional transport semi continuous turbidity currents are thought to have been generated by retrogressive slumping of ice proximal well sorted sandy deposits on the delta front and slope the lateral and vertical changes of lithofacies within the sandy lobe are mainly attributed to normal mechanisms of turbiditic lobe growth with only minor effect from synsedimentary glacier terminus movement and minor changes in the meltwater outflow position this detailed mapping of facies changes allows a fairly accurate reconstruction of the axis of the former discharge outlet

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

sedimentary environments and facies in an arctic basin itirbilung fiord baffin island canada abstract itirbilung fiord typifies a deep arctic basin that experiences episodic sedimentation events cycled principally by aeolian transport nival and glacier melt with punctuations by mass sediment failures a quaternary sedimentary fill exceeding 150 m is found in two of the fjord s four sub basins basin circulation is associated with meltwater influx during the summer wind generated drift during the fall accompanied by deep water exchanges winter isohaline generated circulation and tidal currents which operate over the entire year sediment accumulation decreases down the basin this general trend is interrupted by side entry fan deltas that locally contribute large volumes of sediment basin deposits are largely ponded between the fjord walls although two of the fjord s sills are mantled by hemipelagic deposits five seismo stratigraphic units are identified and may represent sedimentary deposits associated with a single phase of ice sheet advance and retreat the upper three seismic units were cored and contain seven sedimentary facies that show little correlation between sub basins pebbly sandy mud from the melt of debris laden ice burrowed mottled mud reflecting the bioturbation of hemipelagic deposits wispy laminated mottled mud from low velocity currents and or melt out of seasonal sea ice cover and bioturbation laminated sand and mud from the hypopycnal flows from rivers graded coarse sand gravel and pebbly sand and sand reflecting very rapid deposition from high concentration turbidity currents or from sandy debris flows and cross bedded sands that may relate to the reworking of turbidity current deposited sands possibly by reverse flow mechanisms

depositional settings and evolution of a fjord system during the carboniferous glaciation in northwest argentina abstract fjord systems represented by glacial diamictites and postglacial transgressive shales formed in the basins of western argentina during the late carboniferous gondwana glaciation well exposed fjord deposits of the guandacol formation were studied in the loma de los piojos region protoprecordillera where they fill a 2 9 km wide paleovalley with steep side walls and a relatively flat floor the valley cross cuts lower devonian sandstones and mississippian mudstones and sandstones and provides evidence of glacial abrasion including striated pavements and glacial microtopography grooves ridges and striae based on the analysis of seven sedimentary logs eight sedimentary facies in the valley fill were recognized a massive diamictites b laminated mudstones with dropstones c stratified diamictites d clast supported conglomerates and sandstones e deformed diamictites conglomerates and sandstones f folded diamictites g mudstones interbedded with sandstones and h stacked and amalgamated sandstones these sedimentary facies are grouped into two principal facies assemblages that represent different stages of the paleovalley fill assemblage 1 is composed of diamictites facies a c and f laminated mudstones with dropstones facies b and conglomerates facies d and e which represent glacially influenced sedimentation in the paleovalley assemblage 2 represents the paleovalley fill when glacial influence ceased and comprises laminated mudstones interbedded with sandstones facies g and stacked sandstone beds facies h that mostly record deltaic sedimentation stratigraphic relationships plant fossils found in the paleovalley walls and palynological assemblages recovered in mudstones of facies d help to establish an early pennsylvanian age for both the incision and the filling of the paleovalley the studied paleovalley records an exceptional example of the western gondwanan glacial to postglacial transition due to the continuous stratigraphic succession within the paleovalley as well as palynological megafloristic and radiometric data this example provides a complete framework of the late carboniferous postglacial evolution in western gondwana

decadal interactions between the western tropical pacific and the north atlantic oscillation the relationship between interdecadal variations of tropical sea surface temperature sst in the last 120 years and circulation anomalies related to the north atlantic oscillation nao is investigated in this study using an atmospheric general circulation model agcm we confirm observational evidence that variations in the sst gradient in the western tropical pacific are related to the nao anomalies on decadal timescale and may be contributing to the shift towards the positive nao phase observed in the late 20th century the role played by the indian ocean nao teleconnection advocated in recent studies focused on the last 50 years is also assessed in the context of the 120 year long record it is suggested that a positive feedback between the pacific sst and the hemispheric circulation pattern embedding the decadal nao signal may act to enhance the internal variability of the coupled ocean atmosphere system and justify the stronger teleconnection found in observational data than in sst forced agcm experiments

structural transect of the western transverse ranges california implications for lithospheric kinematics and seismic risk evaluation a retrodeformable cross section that integrates surface and subsurface data across the western transverse ranges california illustrates an actively developing fold and thrust belt that began forming at 2 3 ma high level thrusts are interpreted to root in a mid crustal detachment at 12 15 km depth which coincides with the maximum depth of earthquakes the cross section documents 53 km of convergence above the mid crustal detachment dividing this by the time since onset of deformation yields convergence rates of 17 6 26 5 mm yr the high density lithospheric anomaly beneath the transverse ranges is related to subduction of lower crust and lithosphere below the mid crustal detachment to balance the shallow crustal shortening thrust ramps coincide with zones of high seismicity in the transverse ranges this suggests that ramp regions have the highest potential for compressive earthquake events e g the recent whittier narrows earthquake of october 1 1987 m sub l 5 9 occurred along the eastern part of a ramp zone

crustal strain near the big bend of the san andreas fault analysis of the los padres tehachapi trilateration networks california in the region of the los padres tehachapi geodetic network the san andreas fault saf changes its orientation by over 30 degree from n 40 degree w close to that predicted by plate motion for a transform boundary to n 73 degree w the strain orientation near the saf is consistent with right lateral shear along the fault with maximum shear rate of 0 38 plus minus 0 01 mu rad yr at n 63 degree w in contrast away from the saf the strain orientations on both sides of the fault are consistent with the plate motion direction with maximum shear rate of 0 19 plus minus 0 01 mu rad yr at n 44 degree w the strain rate does not drop off rapidly away from the fault and thus the area is fit by either a broad shear zone below the saf or a single fault with a relatively deep locking depth the fit to the line length data is poor for locking depth d less than 25 km for d of 25 km a buried slip rate of 30 plus minus 6 mm yr is estimated the authors also estimated buried slip for models that include the garlock and big pine faults in addition to the saf slip rates on other faults are poorly constrained bymore the los padres tehachapi network the best fitting garlock fault model had computed left lateral slip rate of 11 plus minus 2 mm yr below 10 km buried left lateral slip of 15 plus minus 6 mm yr on the big pine fault within the western transverse ranges provides significant reduction in line length residuals however deformation there may be more complicated than a single vertical fault a subhorizontal detachment on the southern side of the saf cannot be well constrained by these data the authors investigated the location of the saf and found that a vertical fault below the surface trace fits the data much better than either a dipping fault zone located south of the surface trace less

sedimentary imprints of former ice sheet margins insights from an end ordovician archive sw libya fromthe proterozoic to the quaternary the evolution of the earthwas characterised by recurrent periods of glaciation however the margins of many ancient ice sheets are poorly defined on palaeogeographic reconstructions the extent and outlines of ancient ice sheets can be better understood through careful documentation of sediments deposited at the ice sheet margin an outstanding example is provided herein based on an end ordovician archive in libya tihemboka area murzuq basin the four sets of structures include i subglacial glaciotectonic structures and soft sediment deformations from flowing glacier ice such as intraformational glacial striae intraformational deformation shear planes sheath folds normal microfaults and large scale glaciotectonic folds and thrusts ii structures resulting from overpressured subglacial meltwater flows such as clastic dykes and tunnel valleys iii proglacial depositional structures and facies related to highmagnitude meltwater floods such as sandstone intraclasts large scale bedforms resulting from supercritical flows climbing dune cross stratification and kettle holes and iv deformation structures resulting from free floating and nonglacier ice such as ice keel scours and ice crystal marks such a set of structures points to an ice marginal essentially continental depositional setting and provides an excellent suite of criteria to identify margins of ancient ice sheets in the stratigraphic record at a regional scale a reconstruction through time and space of the related depositional wedge is proposed this corresponded to a seismic scale n120 m in thickness 40 km in length ice marginal wedge in front of an essentially warm based ice sheet inducing concomitant large scale glaciotectonic deformation glacial basin and tunnel valley downcuttings the related ice front was associated with high energy meltwater flows feeding a network of deeply incised proglacial channels downstream and beyond them a fluvioglacial deltaic system shallow ice marginal permafrost most likely affected the depositional wedge at a larger scale the tihemboka ice marginal wedge is interpreted as related to a stillstand period over the gondwana platform developed over an estimated interval of a few thousands of years based on these data the conditions that arose in a particularly favourable context for the development the preservation and the identification of ice marginal wedges in the geological record are reviewed significant meltwater derived sediment deposition and aggradation in an accommodation space resulting either from preglacial inheritance glacial downcuttings and or glacio isostatic lithospheric flexure or active tectonic subsidence 1 myr are required for their formation and subsequent preservation

depositional models for the glaciomarine sequences of andean late paleozoic basins of argentina abstract diamictite bearing late paleozoic sequences of probably glacial origin crop out in three basins of western argentina 1 the tarija basin 2 the calingasta uspallata basin and 3 the central patagonian basin the tarija section shows clear evidence of soft sediment deformation in a shallow marine environment slump overfolds and hook like and pull apart structures are common in lenses of well sorted sandstones within a sequence mostly composed of massive matrix supported pebbly mudstones the overall shallowing upward trend of the section suggests alluvial progradation underlying fine grained rocks represent quiet water prodelta deposits the diamictites suggest a delta slope position and the overlying red mudstones with cross bedded sandstones and conglomerates correspond to delta plain deposits in the calingasta uspallata basin the hoyada verde formation represents the best example of an ice contact glaciomarine depositional system with minor gravity flow deposits massive matrix supported sandy diamictites associated with a boulder pavement together with sandstone and conglomerate channels represent grounded ice deposits grading to subglacial flow tills thin bedded matrix supported muddy diamictites with dropstones are the product of a process of gravity resedimentation debris flows and ice rafting pebbly shales represent shelf sedimentation with local deposition from floating ice the ansilta formation shows characteristic features of low and high turbidity current dominated environments basal diamictites resemble debris flow deposits and are associated with thickening upward sequences of bouma tb c turbidites and massive sandstones with fluid scape structures these two sections described above represent the end members of a continuum from glaciomarine rocks to gravity induced deposits formed by subaqueous reworking of glacial debris fine grained rocks associated with diamictites contain marine fossils belonging to the livipustula zone of westphalian age middle carboniferous the central patagonian diamictites appear to be clearly associated with classical turbidites with bouma sequences resedimented conglomerates and high density turbidity current sandstones the conglomerates and sandstones form composite channels with common amalgamation and internal scour surfaces the depositional models proposed for the diamictite bearing sequences of the three basins can be placed in a broader model which embraces several types of complex interactions among glaciomarine nearshore and gravity flow dominated environments

discrepancy between geological and geodetic deformation rates in the ventura basin space geodesy provides a new tool for measuring neotectonic deformation which when combined with geological and geophysical observations and models can be used to infer rates and styles of deformation in the ventnra basin region of southern california the geodetically measured convergence rates of 7 10 mm yr 1 ref 1 are significantly lower than the 20 25 mm yr 1 estimated from geological data2 3 here we investigate the possible implications of this discrepancy it might be for example that temporal variations cause the short and long term convergence rates to differ but if this were the case we would expect to observe the long term rate by extending the geodetic measurements over a broader region yet only 11 3 mm yr 1 of regional convergence is observed4 our preferred explanation of the discrepancy is that the geological models require revision and to this end we present two deformation models that satisfy both the geological and geodetic constraints our modelling suggests that the faults bounding the basin are locked at the surface but are slipping at depths below 2 5 km

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

ocean heat transport sea ice and multiple climate states insights from energy balance models abstract several extensions of energy balance models ebms are explored in which i sea ice acts to insulate the atmosphere from the ocean and ii ocean heat transport is allowed to have some meridional structure controlled by the wind with minima at which the ice edge can rest these new models support multiple stable ice edges not found in the classical ebm and a hysteresis loop capable of generating abrupt warming as the ice edge jumps from mid to high latitudes the new equilibria are demonstrated in two classes of model in which the wind stress is either specified externally or generated interactively wind stress is computed by introducing a dynamical constraint into the ebm to represent the simultaneous meridional transport of energy and angular momentum in the atmosphere this wind stress is used to drive ocean gyres with associated structure in their meridional heat transport so that the atmosphere and ocean are coupled together both thermally and mechanically

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

co existing climate attractors in a coupled aquaplanet the first step in exploring the properties of dynamical systems like the earth climate is to identify the different phase space regions where the trajectories asymptotically evolve called attractors in a given system multiple attractors can co exist under the effect of the same forcing at the boundaries of their basins of attraction small changes produce large effects therefore they are key regions for understanding the system response to perturbations here we prove the existence of up to five attractors in a simplified climate system where the planet is entirely covered by the ocean aquaplanet these attractors range from a snowball to a hot state without sea ice and their exact number depends on the details of the coupled atmosphere ocean sea ice configuration we characterise each attractor by describing the associated climate feedbacks by using the principal component analysis and by measuring quantities borrowed from the study of dynamical systems namely instantaneous dimension and persistence

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

seismic triggering of submarine slides in soft cohesive soil deposits abstract the geological profile of many submerged slopes on the continental shelf consists of normally to lightly overconsolidated clays with depths ranging from a few meters to hundreds of meters for these soils earthquake loading can generate significant excess pore water pressures at depth which can bring the slope to a state of instability during the event or at a later time as a result of pore pressure redistribution within the soil profile seismic triggering mechanisms of landslide initiation for these soils are analyzed with the use of a new simplified model for clays which predicts realistic variations of the stress strain strength relationships as well as pore pressure generation during dynamic loading in simple shear the proposed model is implemented in a finite element program to analyze the seismic response of submarine slopes these analyses provide an assessment of the critical depth and estimated displacements of the mobilized materials and thus are important components for the estimation of submarine landslide induced tsunamis

reassessment of mid carboniferous glacial extent in southwestern gondwana rio blanco basin argentina inferred from paleo mass transport of diamictites abstract late paleozoic glacial diamictites occur in many localities in western argentina indicating that the region was strongly affected by glaciation during the mid carboniferous late serpukhovian early bashkirian in most instances these diamictites are found in steeply walled paleovalley settings in the andean precordillera this study presents new data from a locality north of the precordillera that suggests an additional distinct volume of ice existed in the region during the carboniferous the glacigenic diamictites in the rio blanco basin were ultimately emplaced as gravity flows precluding inferences of paleo ice volume fold nose orientation and soft sediment groove orientations within the diamictites indicate that the deposits were emplaced from north to south suggesting that glacial ice was most likely not sourced from the proto precordillera at this locality requiring the need for another ice center to the north of the basin diamictite facies indicates that the sediment was initially supplied to the study area by a warm based glacier

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

postglacial rebound and fault instability in fennoscandia summary the best available rebound model is used to investigate the role that postglacial rebound plays in triggering seismicity in fennoscandia the salient features of the model include tectonic stress due to spreading at the north atlantic ridge overburden pressure gravitationally self consistent ocean loading and the realistic deglaciation history and compressible earth model which best fits the sea level and ice data in fennoscandia the model predicts the spatio temporal evolution of the state of stress the magnitude of fault instability the timing of the onset of this instability and the mode of failure of lateglacial and postglacial seismicity the consistency of the predictions with the observations suggests that postglacial rebound is probably the cause of the large postglacial thrust faults observed in fennoscandia the model also predicts a uniform stress field and instability in central fennoscandia for the present with thrust faulting as the predicted mode of failure however the lack of spatial correlation of the present seismicity with the region of uplift and the existence of strike slip and normal modes of current seismicity are inconsistent with this model further unmodelled factors such as the presence of high angle faults in the central region of uplift along the baltic coast would be required in order to explain the pattern of seismicity today in terms of postglacial rebound stress the sensitivity of the model predictions to the evects of compressibility tectonic stress viscosity and ice model is also investigated for sites outside the ice margin it is found that the mode of failure is sensitive to the presence of tectonic stress and that the onset timing is also dependent on compressibility for sites within the ice margin the evect of earth rheology is shown to be small however ice load history is shown to have larger evects on the onset time of earthquakes and the magnitude of fault instability

glaciomarine sequence stratigraphy in the mississippian rio blanco basin argentina southwestern gondwana basin analysis and palaeoclimatic implications for the late paleozoic ice age during the tournaisian the late palaeozoic ice age lpia has been well recorded in the uppermost mississippian pennsylvanian of gondwana nevertheless little is known about the temporal and geographic dynamics particularly during the early mississippian we report on exceptional tournaisian glaciomarine strati graphic sections from central argentina rio blanco basin encompassing 1400 metres these succes sions contain conspicuous glacigenic strata with age constraints provided by palaeontological data and u pb detrital zircon age spectra a variety of marine glaciomarine and fan deltaic environments indicate relative sea level variations mainly associated with tectonism and repetitive cycles of glacial activity provenance analysis indicates a source from the sierras pampeanas basement located to the east fifteen sequences were grouped into three depositional models 1 transgressive systems tracts tst to high stand systems tracts hst sequences unaffected by glacial ice 2 lowstand systems tracts lst to tst and then to hst with glacial in uence and 3 non glacial falling stage systems tract fsst to tst and hst the glacial evidence indicates that the oldest mississippian glacial stage of the lpia in southwestern gondwana is constrained to the middle tournaisian in contrast with previous descriptions of gondwanan coeval glacial records our sequence analysis confirms complex hierarchical climate varia bility rather than a single episode of ice advance and retreat supplementary material https doi org 10 6084 m9 figshare c 5011424

co seismic displacements of the 1994 northridge california earthquake the 17 january 1994 northridge california earthquake significantly deformed the earth s crust in the epicentral region displacements of 66 survey stations determined from global positioning system gps observations collected before and after the earthquake show that individual stations were uplifted by up to 417 5 mm and displaced horizontally by up to 216 3 mm using these displacements we estimate parameters of a uniform slip model fault geometry and slip are estimated independent of seismological information using monte carlo optimization techniques that minimize the model residuals the plane that best fits the geodetic data lies 1 to 2 km above the plane indicated by aftershock seismicity modeling for distributed slip on a coplanar yet larger model fault indicates that a high slip patch occurred up dip and northwest of the mainshock hypocenter and that less than 1 m of slip occurred in the uppermost 5 km of the crust this finding is consistent with the lack of clear surface rupture and with the notion that the intersection with the fault that ruptured in 1971 formed the up dip terminus of slip in the northridge earthquake displacements predicted by either of these simple models explain most of the variance in the data within 50 km of the epicenter on average however the scatter of the residuals is twice the data uncertainties and in some areas there is significant systematic misfit to either model the co seismic contributions of aftershocks are insufficient to explain this mismatch indicating that the source geometry is more complicated than a single rectangular plane

paleoseismicity the swedish case abstract sweden is part of an old cratonic area it was repeatedly glaciated during the quaternary after the 20 ka glaciation maximum it has experienced a glacial isostatic uplift of over 800 m numerous paleoseismic indices have been recorded giving evidence of frequent high magnitude earthquakes from the time at around and just after the deglaciation late holocene archaeoseismic fracturing is also reported these observations violate all claims of a possible safe long term repository for high level nuclear waste some 500 m down in the bedrock

late paleozoic paleoclimatology of central west argentina abstract based on sedimentologic and paleontological characteristics present in the sedimentary record of the calingasta uspallata and paganzo basins a model of paleoclimatic evolution for the late paleozoic of central west argentina is proposed additional evidence is also provided by data from other basins of southern san rafael and tepuel basins and northern tarija basin west argentina five paleoclimatic stages have been defined paleoclimatic stage i tournalism visean early carboniferous is characterized by temperature and humid preglacial conditions as evidencedin the el raton and maliman formations calingasta uspallata basin plant remains of archeosigillaria and lepidodendropsis zone are present in both units the paleoclimatic stage ii namurian early westphalian middle carboniferous comprises widespread glacial deposits including glaciomarine sequence in the westernmost basins calingasta uspallata western paganzo san rafael and tepuel and terrestrial tillites and glaciolacustrine fine clastics in some areas of the paganzo basin fossils of the levipustula fauna are distinctive in the glaciomarine deposits of this stage and in the overlying postglacial fine clastics of the basal portion of stage iii substage iiia the paleoclimatic stage iii of middle carboniferous late westphalian age corresponds to postglacial transgressions that flooded the previously glaciated shelves in the calingasta uspallata and tepuel basins terminal glaciolacustrine deposits substage iiia indicate of the demise of glacial conditions and coal measures of fluvial affinity in the paganzo basin substage iiib probably this postglacial stage was characterized by high humidity and moderate temperatures this stage is paleobiologi defined by a floral assemblage known as nbg nothorhacopteris botrychiopsis and ginkgophyllum the paleoclimatic stage iv late carboniferous stephanian early permian corresponds to a time interval characterized by seasonally dry climates and a progressive amelioration in humidity clear evidence of these climatic conditions is present in several localities in the paganzo basin the first astherothecae and glossopteris leaves are found finally paleoclimatic stage v middle late permian is dominated by red beds thick eolian sequences and saline lake facies deposited under arid to semi arid conditions coeval volcanism derived from the west is expressed by interbedded tuffs and agglomerates calingasta uspallata paganzo and san rafael basins

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

the subsurface record of the late palaeozoic glaciation in the chaco basin bolivia the late palaeozoic glaciation was the longest of the phanerozoic era it is recorded in numerous gondwanan basins with some such as the chaco basin having a high petroleum potential in this basin the quality of the available seismic well and outcrop data permits us to characterize the late palaeozoic glacial record palaeovalleys that are c 500 m deep and c 7 km wide have been analysed here focusing on the glaciogenic carboniferous deposits seismic data with well ties and outcrop analogues provide new sedimentological insights the palaeovalley infill is imaged as a chaotic seismic facies overlain by an aggrading prograding prism interpreted as tillites covered by a fluvio deltaic system tillites form both under the ice and during rapid ice recession whereas fluvio deltaic systems can only originate from a stable ice margin and last until the ice sheets withdraw inland these two depositional modes are repeated several times generating a progressive burial of the carboniferous palaeovalleys this succession of erosions and fills records major glacial stages including a series of glacial and interglacial phases from the late devonian to the early permian depicting the late palaeozoic glacial history of the chaco basin seems crucial for the localization of potential good reservoirs

geodetic observations of the m 5 1 january 29 1994 northridge aftershock geodetic observations of the january 29 1994 m 5 1 aftershock of the northridge earthquake are consistent with seismic solutions showing left lateral oblique slip on a northeast striking steeply dipping fault thirty second solutions of the data from the station showing the maximum observed displacement 35 mm indicate neither precursory nor immediate post seismic motion to the aftershock the aftershock does appear to be superimposed over the longer term northridge post seismic deformation field inversions of the data yield a potency of 2 6 0 3 x 10 3 km 3 slightly higher than that determined by seismic methods combining the potency with estimates of rigidity from p and s wave velocities yields a moment that is consistent with seismic moment solutions

glacial rebound and sea level change in the british isles observations of sea levels around the coastline of the british isles for the past 10 000 15 000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the late devensian ice sheet a high resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea level change and which demonstrates that the observations are the result of i the glacio isostatic crustal rebound in response to the unloading of the ice sheet over britain and to a lesser degree of the ice sheet over fennoscandia and ii the rise in sea level from the melting late pleistocene ice sheets including the response of the crust to the water loading the hydro isostatic effect the agreement between model and observations is such that there is no need to invoke vertical crustal movements for great britain and ireland of other than glacio hydro isostatic origin the rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea level change to approximate the eustatic sea level rise the observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation preliminary solutions are presented which indicate an upper mantle viscosity of 3 5 1020 pas a lithospheric thickness of about 100 km or less and an ice model that was not confluent with the scandinavian ice sheet during the last glaciation and whose maximum thickness over scotland is unlikely to have exceeded about 1500 m

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

linking glacial interglacial states to multiple equilibria of climate glacial interglacial cycles are often described as an amplified global response of the climate to perturbations in solar radiation caused by oscillations of earth s orbit however it remains unclear whether internal feedbacks are large enough to account for the radically different glacial and interglacial states here we provide support for an alternative view glacial interglacial states are multiple equilibria of the climate system which exist for the same external forcing we show that such multiple equilibria resembling glacial and interglacial states can be found in a complex coupled general circulation model of the ocean atmosphere sea ice system the multiple states are sustained by ice albedo feedback modified by ocean heat transport and are not caused by the bi stability of the ocean s overturning circulation in addition expansion contraction of the southern hemisphere ice pack over regions of upwelling regulating outgassing of co 2 to the atmosphere is the primary mechanism behind a large pco 2 change between states

recent fault movement and palaeoseismicity in western scotland abstract field study at two locations in western scotland is described and gives evidence for fault movement and seismic activity during the late and post glacial epochs the evidence comprises levelling survey of raised marine shorelines remote sensing study of lineaments radiocarbon dating of quaternary sediment and detailed field examination of faults and fault gouge material vertical fault displacements of up to 3 m are observed on a c 10 500 year old raised marine shoreline on the isle of mull and repeated predominantly lateral movement is observed on a prominent 14 km long fault lineament active since ice retreat and as recently as c 2000 yrs b p the fault movements are located close to the edge of the area formerly covered by the loch lomond readvance ice cap 11 000 10 000 yrs b p they are considered to have been caused by rapid rates of isostatic rebound soon after deglaciation

stress loading from viscous flow in the lower crust and triggering of aftershocks following the 1994 northridge california earthquake following the m w 6 7 northridge earthquake significant postseismic displacements were resolved with gps using a three dimensional viscoelastic model we suggest that this deformation is mainly driven by viscous flow in the lower crust such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate most aftershocks within the rupture zone especially those that occurred after the first several weeks of the main shock may have been triggered by continuous stress loading from viscous flow the long term decay time of aftershocks about 2 years approximately matches the decay of viscoelastic loading and thus is controlled by the viscosity of the lower crust our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow

fennoscandian earthquakes whole crustal rupturing related to postglacial rebound local and regional earthquake locations provide seismic evidence that large shield earthquakes have occurred in northern fennoscandia these paleoearthquakes with fault lengths of up to 160 kilometers and average displacements of up to 15 meters were triggered by nonisostatic compressive stresses caused by the removal of the ice at the end of the last deglaciation the fennoscandian faults were probably formed by single events that ruptured through most of the crust the largest event moment magnitude mw 8 2 was larger than other known stable continent earthquakes outside failed rifts or extended crust

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

deformation in the santa barbara channel from gps measurements 1987 1991 geodesy is one of the few techniques that can be used to estimate strain rates across the submerged structures in the santa barbara channel by resolving relative surface velocities the global positioning system gps can be used to infer crustal deformation rates independent of geologic models gps measurements from the period 1987 1991 have been used to derive velocities for a 8 station network bounding the channel these estimates are based on 10 gps experiments each of several days in length over this 4 5 year period precision of individual determinations of intersite vectors range from 3 to 7 mm for the horizontal components and average 20 mm in the vertical the gps data indicate high rates of shortening in the eastern channel 6 1 mm yr at n16 3e and low rates of deformation in the western channel comparisons with previous geodetic studies suggest that deformation in the region has not been uniform over the last 100 years

the magnitude 6 7 northridge california earthquake of january 17 1994 the most costly american earthquake since 1906 struck los angeles on 17 january 1994 the magnitude 6 7 northridge earthquake resulted from more than 3 meters of reverse slip on a 1 5 kilometer long south dipping thrust fault that raised the santa susana mountains by as much as 70 centimeters the fault appears to be truncated by the fault that broke in the 1971 san fernando earthquake at a depth of 8 kilometers of these two events the northridge earthquake caused many times more damage primarily because its causative fault is directly under the city many types of structures were damaged but the fracture of welds in steel frame buildings was the greatest surprise the northridge earthquake emphasizes the hazard posed to los angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes

effects of mass wasting on the stratigraphic architecture of a fjord valley fill correlation of onshore shear wave seismic and marine seismic data at trondheim norway abstract a combined record of onshore high resolution shear wave seismic and marine p wave seismic data shows the near shore stratigraphic organisation of a fjord valley fill at trondheim central norway the overall stratigraphy shows a typical fjord valley fill of up to 160 m in thickness that is composed of glaciomarine and fjord marine sediments overlain by deltaic deposits which in the onshore section are draped by an anthropogenic fill an interval characterised by low shear wave velocities below the onshore anthropogenic fills is shown by sampled drillings to comprise part clay and part organic deposits the seismic record reveals evidence of recurrent mass wasting events that include landslide debris turbidite deposits and channel features a chronological framework for the stratigraphy is provided by existing radiocarbon dates for local deglaciation and mass wasting events the combined onshore offshore datasets document the lateglacial to holocene development of an emerging fjord and delta system affected by major mass wasting events the architectural development of the younger part of the stratigraphy is interpreted as particularly affected by two known mass wasting events each involving several million m 3 of debris a thick layer of debris from a 3500 cal yr event probably resulted in a blockage of the subaqueous channels diversion of turbidity currents and deposition of lateral accretion packages whereby local fjord sedimentation temporarily increased a 2200 cal yr event resulted in a sudden reorganisation of the distributary system whereby distal delta sedimentation abruptly shifted north to northeastwards to an area temporarily subjected to marine erosion during fall of relative sea level the study adds to the understanding of landslides and low stiffness zones in the area of importance for near shore geohazard assessment the study also provides insight into the stratigraphic variability of fjord valley fills and highlights the interplay between fjord marine sedimentation marine abrasion delta progradation and mass wasting during late stages of fjord filling

deglaciation seismotectonics a principal influence on intraplate seismogenesis at high latitudes abstract in many high latitude stable continental regions deglaciation dominates the current crustal strain field interference between polarised tectonic and radial deglaciation strain fields affects the deviatoric stress state and fault stability margins and in consequence both the levels and properties of seismicity throughout glacial loading and unloading the most notable present day affects of this strain interference are predicted to include alternating quadrants of enhanced seismicity and aseismicity around rebound domes and former peripheral forebulges such strain interference can explain much of the geography and timing of holocene earthquake occurrence across northern europe and eastern north america

deformation kinematics in the western united states determined from quaternary fault slip rates and recent geodetic data we estimate the horizontal velocity gradient tensor field from quaternary fault slip rates and recent global positioning system gps and very long baseline interferometry vlbi velocity solutions in the western united states transform plate boundary zone the total velocity obtained from the quaternary fault slip rate data across the entire plate boundary is within 1 mm yr of the nuvel 1a predicted pacific pa north american na plate motion velocity but directions are 5 6 anticlockwise of directions given by nuvel 1a the total velocity obtained from inversion of recent geodetic data is 2 3 anticlockwise from the nuvel 1a na pa velocity but the difference between the two is not significant at the 95 confidence level the discrepancy between the total pa na motion obtained from the geological data and nuvel 1a indicates that a marginally significant amount of ne sw shortening possibly as much as 5 mm yr is missing overall in the geologic data shortening may occur in the long term in the offshore and coastal areas of california where such shortening is required in the shorter term geodetic solution the seismic moment released in the last 148 years is 59 of the total moment release rate expected from long term strain rate field including both seismic and aseismic deformation derived from the inversion of geological data with nuvel 1a far field pa na motion constraints the accumulated strain in the areas containing the southern san andreas fault san jacinto fault the san francisco bay area and the area containing the ventura basin in the western transverse ranges in the last 148 years is the equivalent to that which could be released by an mw 7 0 earthquake in each 50 100 15 km3 crustal volume if strain is to be released seismically in these areas

deglacial paleoseismicity in sweden the 9663 bp iggesund event abstract the iggeesund event is an example of the high seismicity which occurred in fennoscandia during deglaciation as a function of the high rate of glacial isostatic uplift this event is dated to varve 9663 bp the iggesund hudiksvall area is represented by intensive postglacial fracturing of the bedrock recorded over an area of at least 50 50 km the most remarkable locality is the boda cave system a hill fractured into a field of large detached blocks with a cave system of more than 2 km length in the varve year 9663 bp an extensive turbidite was spread over an area of 210 80 km liquefaction structures are recorded over an area of 80 30 km and can be assigned to the same varve year structures and deposits of a tsunami are recorded over 80 50 km

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

late paleozoic paleofjord in the southernmost parana basin brazil geomorphology and sedimentary fill abstract in the southernmost part of the parana basin records of the late paleozoic glaciation occur in a discontinuous form preserved in paleovalley systems excavated in the crystalline basement this paper addresses one of these paleovalleys the mariana pimentel which extends over 60 km with nw se valley direction and a constant width of 2 5 km with the objective of demonstrating that the paleovalley worked as a fjord during the glaciation period its origin as well as sedimentary fill and morphology were analyzed the paleovalley morphology was obtained through electrical resistivity electrical sounding and lateral mapping and mathematical modeling in four transverse sections the morphology of the paleovalley documented by the u shape steady width and high depth reaching up to 400 m are typical features of modern glacial valleys the sedimentary facies that fill the base of the paleovalley such as rhythmites and dropstones with thickness up to 70 m and diamictites with faceted pebbles up to 5 m thick are signs of its glacial origin during the glaciation period the paleovalley had a connection to the epicontinental sea located to the northwest extended toward namibia and was excavated by glaciers from the highlands of this region thus the evidence attests that the mariana pimentel paleovalley was a fjord during the late paleozoic glaciation the duration of the late paleozoic glaciation which is longer than the quaternary glaciation the apatite fission track that suggests erosion up to 4 km thick in the study area and the lack of preserved hanging valleys in the mariana pimentel indicate that the paleovalley once featured a higher dimension furthermore the existence of paleofjords excavated in the border of the basement corroborates the idea of small ice centers controlled by topography during the late paleozoic glaciation

deformation following the 1994 northridge earthquake m 6 7 southern california following the 1994 mw 6 7 northridge earthquake a 65 km long north south array of 11 geodetic monuments was established across the rupture the array was surveyed with gps ten times in the 4 25 yr after the earthquake although there is evidence for modest nonlinear postseismic relaxation in the first few weeks after the northridge earthquake the deformation in the subsequent four years can be adequately described by constant station velocities the observed s70 e velocity components are consistent with the deformation expected from steady strain accumulation on the san andreas fault the n20 e velocity components indicate that the southern northridge fault block is moving almost as a unit n20 e with repect to the northern fault block the motion being accommodated by a zone of convergence width 20 km at the north end of the northridge rupture

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

the role of oceans and sea ice in abrupt transitions between multiple climate states the coupled climate dynamics underlying large rapid and potentially irreversible changes in ice cover are studied a global atmosphere ocean sea ice general circulation model with idealized aquaplanet geometry is forced by gradual multi millennial variations in solar luminosity the model traverses a hysteresis loop between warm ice free conditions and cold glacial conditions in response to 6 5wm 22 variations in global annual mean insolation comparison of several model configurations confirms the importance of polar ocean processes in setting the sensitivity and time scales of the transitions a sawtooth character is found with fasterwarmingandslowercooling reflectingtheopposingeffectsofsurfaceheatingandcoolingonupper ocean buoyancy and thus effective heat capacity the transition from a glacial to warm equable climate occurs in about 200 years in contrast to the freshwater hosing scenario transitions are driven by radiative forcing and sea ice feedbacks the ocean circulation and notably the meridional overturning circulation moc does not drive the climate change the moc and associated heat transport collapses poleward of the advancing ice edge but this is a purely passive response to cooling and ice expansion the moc does however play a key role in setting the time scales of the transition and contributes to the asymmetry between warming and cooling

stable waterbelt climates controlled by tropical ocean heat transport a nonlinear coupled climate mechanism of relevance to snowball earth ongoing controversy about neoproterozoic snowball earth events motivates a theoretical study of stability and hysteresis properties of very cold climates a coupled atmosphere ocean sea ice general circulation model gcm has four stable equilibria ranging from 0 to 100 ice cover including a waterbelt state with tropical sea ice all four states are found at present day insolation and greenhouse gas levels and with two idealized ocean basin configurations the waterbelt is stabilized against albedo feedback by intense but narrow wind driven ocean overturning cells that deliver roughly 100 w m 2 heating to the ice edges this requires three way feedback between winds ocean circulation and ice extent in which circulation is shifted equatorward following the baroclinicity at the ice margins the thermocline is much shallower and outcrops in the tropics sea ice is snow covered everywhere and has a minuscule seasonal cycle the waterbelt state spans a 46 w m 2 range in solar constant has a significant hysteresis and permits near freezing equatorial surface temperatures additional context is provided by a slab ocean gcm and a diffusive energy balance model both with prescribed ocean heat transport oht unlike the fully coupled model these support no more than one stable ice margin the position of which is slaved to regions of rapid poleward decrease in oht convergence wide ranges of different climates including the stable waterbelt are found by varying the magnitude and spatial structure of oht in both models some thermodynamic arguments for the sensitivity of climate and ice extent to oht are presented

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

neotectonics and paleoseismicity within the stockholm intracratonal region in sweden abstract a number of sites with fresh faults and fractures have been mapped in detail their postglacial and sometimes late glacial age is confirmed they form simple and similar patterns consistent with stress release due to a combination of acting forces they are associated with the peak rate of glacial isostasy and increased strain rates by two orders of magnitude they often cut straight across bedrock hills between so called weak zones the fault throws correspond to approximately magnitude 7 on the richter scale sedimentary and morphological data confirm the seismo tectonic origin newly discovered large scale network of crossing faults is found to have changed the course of the stockholm esker in a way that reveals at least two major seismo tectonic events this is consistent with paleoseismic events of magnitude 7 or more

late pennsylvanian aridification on the southwestern margin of gondwana paganzo basin nw argentina a regional expression of a global climate perturbation abstract paleosols of the paganzo group preserve a shift from the cool climate of the glaciated high latitudes of gondwana to a long term aridification punctuated by shorter term fluctuations in moisture regime in the late carboniferous a quantitative reconstruction of paleoclimate inferred from the major element chemistry of paleosol horizons and the stable isotope geochemistry of soil formed minerals and organic matter indicates that the climate varied substantially during deglaciation along the southwestern margin of gondwana in the middle pennsylvanian including two geologically abrupt shifts to notably drier conditions this dynamic climate terminates in a dry subhumid moisture regime characterized by steppe dry scrub floral provinces quantitative estimates of net primary production during the post glacial interval inferred from paleosol major element geochemistry are consistent with a mesic soil temperature regime in agreement with paleotemperatures inferred from pedogenic goethite d and 18 o contemporaneous aridification is well expressed in paleotropical continental records with middle to late pennsylvanian aridification coincident with an abrupt evolutionary change in many marine and terrestrial species the synchrony of aridification between the high and low paleo latitudes and concomitant major restructuring of some ecosystems suggests that a paleoclimate change of global nature occurred during the moscovian and kasimovian

stratigraphy and palynology of a late paleozoic glacial paleovalley in the andean precordillera argentina fil limarino carlos oscar consejo nacional de investigaciones cientificas y tecnicas oficina de coordinacion administrativa ciudad universitaria instituto de geociencias basicas aplicadas y ambientales de buenos aires universidad de buenos aires facultad de ciencias exactas y naturales instituto de geociencias basicas aplicadas y ambientales de buenos aires argentina

the jormungand global climate state and implications for neoproterozoic glaciations 1 geological and geochemical evidence can be interpreted as indicating strong hysteresis in global climate during the neoproterozoic glacial events 630 ma and 715 ma standard climate theory only allows such strong hysteresis if global climate enters a fully glaciated snowball state however the survival of photosynthetic eukaryotic marine species through these glaciations may indicate that there were large areas of open ocean a previously proposed slushball model for neoproterozoic glaciations could easily explain the survival of these organisms because it has open ocean throughout the tropics but there is only a small amount of hysteresis associated with the slushball state in this paper a new state of global climate the jormungand state is proposed in this state the ocean is very nearly globally ice covered but a very small strip of the tropical ocean remains ice free the low ice latitude of the jormungand state is a consequence of the low albedo of snow free bare sea ice if the ice latitude propagates into the subtropical desert zone it can stabilize without collapsing to the equator because subtropical ice covered regions have a relatively low top of atmosphere albedo as a result of the exposure of bare sea ice and relatively lower cloud cover moreover there is strong hysteresis associated with the jormungand state as greenhouse gas levels are varied because of the high albedo contrast between regions of bare and snow covered sea ice the jormungand state is illustrated here in two different atmospheric global climate models and in the budyko sellers model by offering a scenario that could explain both strong hysteresis in global climate and the survival of life the jormungand state represents a potential model for neoproterozoic glaciations although further study of this issue is needed

snowball versus slushball earth dynamic versus nondynamic sea ice 1 modeling studies of the neoproterozoic snowball earth offer two variations for snowball conditions the original hard snowball earth where the ocean is completely covered by sea ice and an alternate slushball earth or soft snowball where there is an equatorial oasis of open water we use the university of victoria earth system climate model to show that the soft snowball result is only possible when dynamics are excluded from the sea ice component of the model using a purely thermodynamic sea ice component the soft snowball condition is stable whereas with a dynamic and thermodynamic sea ice component it is not as the behavior of dynamic sea ice largely depends on wind stress we compare simulations using two different wind fields a zonally averaged present day wind field and a wind field derived by a general circulation model the fast ocean atmosphere model using neoproterozoic conditions another consequence of using dynamic sea ice is that the sea ice does not become sufficiently thick to flow under its own weight when there is open water this suggests that sea glacier dynamics are not important for snowball inception

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

postseismic deformation associated with the 1992 m ω 7 3 landers earthquake southern california following the 1992 m 7 3 landers earthquake a linear array of 10 geodetic monuments at roughly 5 km spacing was established across the emerson fault segment of the landers rupture the array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it the array was surveyed by global positioning system 0 034 0 048 0 381 1 27 1 88 2 60 and 3 42 years after the landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation the temporal behavior is described roughly by a short term decay time 84 23 days exponential relaxation superimposed upon an apparently linear trend because the linear trend represents motions much more rapid than the observed preseismic motions we attribute that trend to a slower decay time greater than 5 years postseismic relaxation the curvature of which cannot be resolved in the short run 3 4 years of postseismic data about 100 mm of right lateral displacement and 50 mm of fault normal displacement accumulated across the geodetic array in the 3 4 year interval covered by the postseismic surveys those displacements are attributed to postseismic right lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace the right lateral slip amounted to about 1 m directly beneath the geodetic array and the fault normal displacement is apparently primarily a consequence of the curvature of the rupture these conclusions are based upon dislocation models fit to the observed deformation however no dislocation model was found with rms residuals as small as the expected observational error

submarine slide scars and mass movements in karmsundet and skudenesfjorden southwestern norway morphology and evolution abstract shallow seismic sections multibeam bathymetric images and geotechnical investigations of the seafloor in karmsundet and skudenesfjorden sw norway have revealed the occurrence of large slide scars and associated mass movement deposits the slide escarpments are up to 30 40 m high and 8 km long with up to 20 10 6 m 3 of sediment released during a single event of retrogressive sliding the slide scars show a range of associated seafloor topography reflecting various modes of sediment displacement the variation in the escarpment morphology and sediment deformation style can be attributed to the varied intensity of liquefaction sliding involved mud deposits of allerod younger dryas to early holocene age but partly also deposits older than ca 12 000 14 c years bp the sediment failures were probably triggered by seismic reactivation of a local fault by postglacial regional isostatic rebound prior to failure the seafloor deposits were undercompacted and metastable due to high pore pressure the presence of shallow gas and the relatively steep local slope created by the formation of a major scour trough by sea currents minor gravitational sliding may still occur along some of the escarpments although engineering slope stability analysis indicates that the deposits can be regarded as stable in the present day conditions of static load and the anticipated weak sporadic earthquakes with an occurrence likelihood of 10 4 year and a peak acceleration of 0 25 g

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

postglacial faulting in eastern canada nature origin and seismic hazard implications abstract at more than 70 locations in southeastern canada and the adjacent united states tiny bedrock faults displace glacial striations that are about 10 000 years old these reverse faults mostly of small displacement occur in a broad arc from western ontario to newfoundland the faults lie near the margin of the laurentian ice sheet strike generally tangential to it and imply compression nearly normal to the ene directed contemporary regional stress these observations and some age relationships suggest that the faults formed very soon after deglaciation perhaps in the first few thousand years after ice melting in each place and probably represent the release of stresses caused by flexural deformation of the upper crust although the individual offsets are small the faults are believed to be pervasive and individual outcrops reflect amounts of stress relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

earthquake and flood induced turbidites in the saguenay fjord quebec a holocene paleoseismicity record abstract a 38 m long piston core from the deep basin of the saguenay fjord quebec recorded rapidly deposited layers rdl interpreted to represent major floods and earthquakes over the past 7200 years high resolution physical magnetic and sedimentological analyses revealed at least 14 rdl generally with a sandy base and a light gray color interbedded with hemipelagic sediments digital x radiography and grain size analyses at