middle miocene southern ocean cooling and antarctic cryosphere expansion magnesium calcium data from southern ocean planktonic foraminifera demonstrate that high latitude similar to55degreess southwest pacific sea surface temperatures ssts cooled 6degrees to 7degreesc during the middle miocene climate transition 14 2 to 13 8 million years ago stepwise surface cooling is paced by eccentricity forcing and precedes antarctic cryosphere expansion by similar to60 thousand years suggesting the involvement of additional feedbacks during this interval of inferred low atmospheric partial pressure of co2 pco 2 comparing ssts and global carbon cycling proxies challenges the notion that episodic pco2 drawdown drove this major cenozoic climate transition sst salinity and ice volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat vapor transport triggering ice growth and global cooling

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

radiocarbon deglaciation chronology of the thunder bay ontario area and implications for ice sheet retreat patterns the sensitivity of ice sheets to climate change influences the return of meltwater to the oceans here we track the laurentide ice sheet along a w400 km long transect spanning about 6000 yr of retreat during the major climate oscillations of the lateglacial thunder bay ontario is near a major topographic drainage divide thus terrestrial ablation processes are the primary forcers of ice margin recession in the study area during deglaciation three major moraine sets were produced and have been assigned minimum ages of 13 9 0 2 12 3 0 2 12 1 0 1 and 11 2 0 2 cal ka bp from south to north these define a slow retreat w10 50 m a prior to major climate oscillations which was then followed by

cold based laurentide ice covered new england s highest summits during the last glacial maximum to better understand glacial history and process in new england northeastern united states a mountainous area overrun by the laurentide ice sheet we measured three cosmogenic nuclides in nine upland samples the concentrations of 10be and 26al in some samples collected near the summits of katahdin maine and mount washington and little haystack mountain new hampshire are 2 10 times higher than expected for a single exposure period considering field evidence indicating that continental ice covered all new england peaks during the last glacial maximum in situ 14c exposure ages from the summits are much younger suggesting that high elevation sampling sites were ice covered before and during the last glacial maximum field and isotopic data are consistent with new england summits being covered in part by cold based continental ice that did not erode much rock the contrast in erosion rates between stable summits and deeply eroded valleys likely contributes to the development and maintenance of northern appalachian topography

paleoenvironmental reconstruction of the early to middle miocene central paratethys using stable isotopes from bryozoan skeletons stable carbon and oxygen isotope values from single bryozoan colonies were used to reconstruct the paleoenvironments of the early to middle miocene ottnangian to badenian sediments of the central paratethys this approach utilizes a locally abundant allochem while avoiding matrix and multiple allochem contamination from bulk rock samples bryozoan colonies and a few foraminifera and rock matrix samples from 14 localities yielded 399 carbon and oxygen isotope values data from six of the localities 15 of the total number of samples were interpreted as having been diagenetically altered and were rejected the remaining data indicate a primarily localized upwelling signal with lesser variation caused by global climatic and regional tectonic forcing of sea level salinity and temperature paleotemperatures were calculated to range from 12 to 21 c despite potential taxonomic and diagenetic problems bryozoan colonies are a powerful underutilized source of paleoenvironmental carbon and oxygen isotope data

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

southern laurentide ice sheet retreat synchronous with rising boreal summer insolation establishing the precise timing for the onset of ice sheet retreat at the end of the last glacial maximum lgm is critical for delineating mechanisms that drive deglaciations uncertainties in the timing of ice margin retreat and global ice volume change allow a variety of plausible deglaciation triggers using boulder 10 be surface exposure ages we date initial southern laurentide ice sheet lis retreat from lgm moraines in wisconsin usa to 23 0 0 6 ka coincident with retreat elsewhere along the southern lis and synchronous with the initial rise in boreal summer insolation 24 23 ka we show with climate surface mass balance simulations that this small increase in boreal summer insolation alone is potentially sufficient to drive enhanced southern lis surface ablation we also date increased southern lis retreat after ca 20 5 ka likely driven by an acceleration in rising isolation this near instantaneous southern lis response to boreal summer insolation before any rise in atmospheric co 2 supports the milankovic hypothesis of orbital forcing of deglaciations

ecospace variability along a carbonate platform at the northern boundary of the miocene reef belt upper langhian austria the south western edge of the leitha mountains in the southern vienna basin austria exposes parts of an upper langhian middle badenian shallow water 30 m carbonate platform the study of its ecospace comprises sedimentological and palaeontological data of 4 up to 36 m thick carbonate sections of the mullendorf quarries which have been logged and subjected to detailed investigation and sampling the sedimentary record is dominated by coralline algal debris sands which represent 7 distinct lithofacies bioclastic coralline algal mollusc facies hyotissa facies isognomon facies coral facies rhodolith facies bryozoan facies all these facies are described in detail in respect to lithology and biota and are palaeoecologically interpreted striking features of these limestone successions are periodical intercalations of coral and mollusc rich horizons their formation had been triggered by water turbidity and low amplitude changes in relative sea level these relations are especially interesting as the platform carbonates formed at the northern edge of the langhian peri mediterranean reef belt water turbidity as ecological master factor and depth played the fundamental role in ecosystem and community expression within ecospace the lateral distribution and the ecological relations between the various facies types allow proposing an ecospace occupation model

formation of compound strike slip fault zones mount abbot quadrangle california abstract numerous strike slip fault zones in granitic rocks of the mount abbot quadrangle california developed from steeply dipping subparallel joints these joints generally were less than 50 m long and were spaced several centimeters to several meters apart some joints subsequently slipped and became small faults simple fault zones formed as oblique dilatant fractures splay fractures linked non coplanar faults side to side and end to end these simple fault zones are as much as 1 km long and accommodated displacements as great as 10 m compound fault zones formed as splay fractures linked small faults and simple fault zones they are as much as several kilometers long and accommodated displacements as great as 100 m these zones are distinctly different from riedel shear zones and the mechanics of their formation are unlikely to be described well by mohr coulomb mechanisms simple and compound fault zones are composed of non coplanar segments that join at steps or bends splay fracture length determines step widths the longest splay fractures occur along the longest fault zones allowing step widths to increase as the length and displacement across the zones increase these findings are consistent with the structure of some active seismogenic faults and they provide a mechanically consistent field based conceptual model for fault zones that grow in basement rocks from a preexisting set of joints

late wisconsinan ice sheet flow across northern and central vermont usa abstract a compilation of over 2000 glacial striation azimuths across northern and central vermont northeastern usa provides the basis for interpreting a sequence of ice flow directions across this area the oldest striations indicate widespread ice flow to the southeast obliquely across the mountains similarly oriented striations between northern vermont and the ice sheet s terminus in the gulf of maine suggest that a broad area of southeast ice flow existed at the last glacial maximum younger striations with more southerly azimuths on both the mountain ridgelines and within adjacent valleys indicate that ice sheet flow trajectories in most areas rotated from southeast to south parallel to the north south alignment of the mountains as the ice sheet thinned this transition in ice flow direction was time transgressive from south to north with the green mountains eventually separating a thick south flowing lobe of ice in the champlain valley from a much thinner lobe of south flowing ice east of the mountains while this transition was taking place yet ice was still thick enough to flow across the mountains ice flow along a narrow 65 km long section of the green mountains shifted to the southwest such that ice was flowing into the champlain valley the most likely process driving this change was a limited period of fast ice flow in the champlain valley a short lived ice streaming event that drew down the ice surface in the valley the advancing ice front during this period of fast ice flow may be responsible for the luzerne readvance south of glens falls new york valley parallel striations across the area indicate strong topographic control on ice flow as the ice sheet thinned

early mesozoic southward migration of cordilleran transpressional terranes oblique plate convergence can cause forearc arc and back arc regions of active margin orogenic belts to behave as semi independent terranes relative to bordering continental and oceanic lithospheric plates these terranes called here transpressional terranes are bound by the subduction zone on one side by arc parallel strike slip faults in the forearc in the volcanic arc or in the back arc region on the other and are underlain by throughgoing basal decollements these terranes undergo shortening in a direction perpendicular to the subduction zone and migrate as coherent structural bodies parallel to the subduction zone along bounding strike slip faults many terranes of the north american cordillera may have behaved in this manner and perhaps did not travel across the pacific basin but rather were always peripheral to north america we propose that during the triassic to mid cretaceous portions of the cordillera borderland generally were displaced southward with respect to the north american craton due to left oblique convergence since the mid cretaceous they moved northward due to right oblique subduction the proposed displacements are consistent with structural paleomagnetic and paleontologic data and with the relative and absolute motions of north america and the pacific basin plates based on hotspot reference frame models

multiproxy reconstruction of the middle miocene požega palaeolake in the southern pannonian basin ne croatia prior to the badenian transgression of the central paratethys sea abstract the pannonian basin of croatia is the largest back arc extensional basin on the european continent located between the alps carpathians and dinarides syn rift subsidence started at 18 ma and predated the onset of the miocene climate optimum mco 17 14 7 ma in this paper we investigate the evolution of the fluvial lacustrine palaeoenvironment just prior to the transgression of the central paratethys sea studies are based on a 17 m thick section of the po ega palaeolake in the southern pannonian basin using palaeobiological mollusks ostracods palynomorphs fish otoliths mineralogical and sedimentological data our results reveal fluctuating freshwater and brackish conditions and a pulsating water budget which we relate to phases in which the basin was alternatively hydrologically open and closed we infer that the alternating environmental conditions can be best explained by dry and wet periods respectively droughts produced stagnant conditions algae overproduction and increased salinity levels supporting the survival of sporadically invading brackish water species the wet periods on the other hand led to lake highstand episodes expansion of lake area and to the widespread development of profundal facies the lake basin eventually became overfilled and connected through outflowing rivers with the central paratethys sea however the absence of brackish marine assemblages in the po ega palaeolake nevertheless indicates that there was no marine water inflow from the central paratethys at that time

cave sediments constrain the latest pleistocene advance of the laurentide ice sheet in the champlain valley vermont usa laurentide ice sheet advance vermont usa

middle miocene seasonal temperature changes in the styrian basin austria as recorded by the isotopic composition of pectinid and brachiopod shells abstract using the isotope record on pectinid and brachiopod shells we reconstructed middle miocene palaeotemperatures for a shelf environment in the styrian basin austria bivalve shells of macrochlamys sp collected from different horizons of the lower badenian leitha limestone show 18 o values in the range of 3 to 0 peedee belemnite the large intrashell variability of 3 indicates significant seawater temperature fluctuation the results suggest that despite the high geographical latitude ca 40 n the climate in southern austria was warm subtropical with a pronounced seasonality at that time in contrast the 18 o isotopic composition of a pectinid flabellipecten sp and an indeterminate terebratulid brachiopod from the siliciclastic deposits overlying the leitha limestone ranges between 0 and 1 this indicates cooler mean annual temperatures and reduced seasonal variations a 39 ar 40 ar age on fresh volcanic biotites shows a value of 14 2 0 1 ma the tuffs containing the biotites are located below the layer containing the terebratulid and the flabellipecten sp the stable isotope and radiogenic data suggest that the drop in temperature is in direct relationship with the east antarctic ice sheet expansion which started at ca 14 ma due to the variation in temperature the subtropical fauna in the retznei quarry disappeared during the early miocene and the biogenic limestones were replaced by clastic sediments the 18 o isotopic profiles from three pectinids collected from the leitha limestone indicate that these grew within ca 1 5 years growth interruptions occurred during the warm season because during this period the pectinids very likely used their energy for the growth and maturation of gonads carbon isotopic compositions vary between 0 and 2 statistical tests show that for some of the analyzed shells the cyclicity of the 13 c profiles may be explained by the temperature dependent fractionation between air co 2 and dissolved bicarbonate

port eliza cave north american west coast interstadial environment and implications for human migrations abstract the timing of late pleistocene glacial advance retreat relative sea level and environmental viability between 25 and 12 5 ka 14 c yrs bp remain a key issue in the feasibility of a coastal migration route for the first north americans this is discussed on the basis of stratigraphic radiometric and faunal data for port eliza cave a raised sea cave on the west coast of vancouver island british columbia ice cover is indicated by the occurrence of 2 m of laminated clay representing deposition in a subglacial lake from immediately below this clay a diverse vertebrate fauna of marmot vole marten cervid and various species of birds and fish was recovered yielding ages of 18 16 ka these dates and others from the region show that ice cover on the outer coast was brief from ca 15 5 14 ka the fish species indicate that relative sea level was close to the cave and that salmon runs were likely present the terrestrial vertebrate fauna is consistent with a cool open parkland environment with maximum summer temperatures cooler than present these conditions lasted until at least 16 ka with a diverse fauna and favorable climate humans could have survived here on a mixed marine terrestrial diet confirming the viability of the coastal migration hypothesis for this portion of the route

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

time calibration of sedimentary sections based on insolation cycles using combined cross correlation dating the gone badenian stratotype middle miocene paratethys vienna basin austria as an example cross correlation between insolation intensities and a combination of sedimentary characters is introduced to obtain precise time calibration of sedimentary cycles the first step is to transfer the section scale into ages using power spectra comparing the main periods with orbital cycles while in the second step the standardized values of sedimentary signals are cross correlated with the standardized insolation curve as an example for the applicability of the method we investigated calcium carbonate organic carbon in a 9 m sampled section from the historical badenian stratotype at baden sooss lower austria comparing courses of geochemical parameters between the historical stratotype and a nearby drilled 102 m scientific core resulted in continuation of the core section into the stratotype cross correlation between magnetic susceptibility ms combined with the negatively correlated calcium carbonate content of the drilled section on the one side and summer solar insolation at 65 northern latitude on the other resulted in an extremely significant correlation between 14 221 and 13 982 ma this is younger than the before estimated time frame 14 379 to 14 142 ma based on cross correlation between ms and the orbital 100 kyr eccentricity and 41 kyr obliquity cycles the direct continuation of the drilled section by the stratotype covering a time span of 17 7 kyr consequently dates the badenian stratotype between 13 982 and 13 964 ma therefore the upper limit of the stratotype assigned to the early badenian puts it close to the langhian seravallian boundary at 13 82 ma demonstrating the need for revising the badenian stratigraphic subdivision based on orbital cycles especially the middle badenian wielician substage

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

evidence from the lake champlain valley for a later onset of the champlain sea and implications for late glacial meltwater routing to the north atlantic abstract ocean circulation models indicate that freshwater runoff from the north american continent during the last deglaciation may have had an effect on north atlantic ocean circulation and thereby have altered regional climate one such example is a flood from lake agassiz which has been proposed by previous workers to have caused the onset of the younger dryas at around 12 850 calibrated years b p by entering the north atlantic through the gulf of st lawrence we present two radiocarbon ages from terrestrial organic sources in the champlain valley that we associate with the pre champlain sea proglacial lake phases a musk ox bone with an ams age of 11 362 115 14 c years b p 13 438 13 020 calibrated years b p and a wood fragment with an ams age of 10 901 76 14 c years b p 12 995 12 793 calibrated years b p these ages together with a glacial lacustrine varve estimate suggest that the initiation of the champlain sea may not have occurred until after the onset of the younger dryas if the lake agassiz flood event occurred before the opening of the champlain sea then the floodwaters would have been diverted down the champlain and hudson valleys to the north atlantic another possibility is that the agassiz flood may have been contemporaneous with the opening of the gulf of st lawrence it is also possible that there may have been a large enough flood produced by meltwater originating in the champlain valley and st lawrence lowlands at the inception of the champlain sea to have affected ocean circulation without the influence of lake agassiz

integrated stratigraphy and 40ar 39ar chronology of early middle miocene sediments from dsdp leg 42a site 372 western mediterranean abstract an integrated magneto biostratigraphic framework is presented for middle miocene sediments of dsdp site 372 located in the western mediterranean detailed biostratigraphic analysis shows a nearly complete sequence of early middle miocene calcareous plankton bioevents in the mediterranean including the lco last common occurrence of the nannofossil sphenolithus heteromorphus which has been astronomically dated in the ras il pellegrin rip section on malta island abels h a hilgen f j krijgsman w kruk r w raffi i turco e zachariasse w j 2005 long period orbital control on middle miocene global cooling integrated stratigraphy and astronomical tuning of the blue clay formation on malta paleoceanography 20 pa4012 doi 10 1029 2004pa001129 11 pp thermal demagnetization of discrete samples revealed a characteristic low temperature component with dual polarities despite a weak paleomagnetic signal the resultant magnetostratigraphic record combined with the calcareous plankton biostratigraphy is straightforwardly correlated to the geomagnetic polarity time scale ck95 of cande and kent cande s c kent d v 1995 revised calibration of the geomagnetic polarity time scale for the late cretaceous and cenozoic j geophys res 100 6093 6095 and the astronomical tuned neogene time scale atnts04 of lourens et al lourens l j hilgen f j laskar j shackleton n j wilson d 2004 the neogene period in gradstein f m ogg j g smith a g eds a geologic time scale cambridge univ press pp 409 440 the subchrons recorded in site 372 succession range from c5br up to c5aar to confirm the magnetostratigraphic calibration 40ar 39ar dating was performed on feldspar of two volcanic ash layers the radio isotopic dating indicates a younger age for these two ash layers compared to the magnetostratigraphic calibrated ages according to the ck95 and atnts04 age models however if the astronomically calibrated age of 28 21 0 04 ma is used for the fish canyon standard fcs the age for the older ash layer exactly matches its atnts04 age ages for bioevents were calculated assuming constant sedimentation rates between magnetostratigraphic age tie points the s heteromorphus lco has an age of 13 54 ma and 13 63 ma according to ck95 and atnts04 respectively which is consistent with the astronomical tuned age of 13 65 ma determined at rip section abels h a hilgen f j krijgsman w kruk r w raffi i turco e zachariasse w j 2005 long period orbital control on middle miocene global cooling integrated stratigraphy and astronomical tuning of the blue clay formation on malta paleoceanography 20 pa4012 doi 10 1029 2004pa001129 11 pp we therefore conclude that the magnetostratigraphic calibration of dsdp site 372 is correct and that for the time being this site can be considered as a reference section for the early middle miocene of the mediterranean region

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

cosmogenic nuclide ages for new england coastal moraines martha s vineyard and cape cod massachusetts usa abstract cosmogenic nuclide exposure ages for 13 glacially transported boulders atop the martha s vineyard moraine ma usa indicate that the southeastern margin of the laurentide ice sheet reached its maximum extent during the last glaciation 23 200 500 yr ago another 10 age determinations from the younger buzzards bay moraine near woods hole ma indicate that this moraine complex was formed 18 800 400 yr ago these ages correlate approximately with the terminations of cooling cycles recorded in greenland ice cores and coeval ice rafting events suggesting that the marginal position of this sector of the ice sheet was tightly coupled to north atlantic climate during the last glacial maximum

benchmark data of a changing sea palaeogeography palaeobiogeography and events in the central paratethys during the miocene abstract the reconstruction and interpretation of terrestrial ecosystems and vegetational patterns in the central european miocene have to take into account the influence of a vast landlocked water body namely the paratethys sea as a northern appendage of the early mediterranean sea it spanned a north south gradient of at least 4 latitude and has been suggested to represent some kind of palaeothermometer which reflected slight expansions or restrictions of climatic belts due to its vulnerable marine connections it was also highly susceptible to major global sea level fluctuations which are reflected in phases of endemism hence a fairly continuous record of marine nearshore assemblages throughout the miocene reflects an extraordinary interplay of sea level fluctuations changes in climate immigrations and blooms in autochthonous elements whilst biostratigraphic implications of these patterns were recognised early in palaeontology a biogeographic model is still lacking the intermingling of palaeogeographic terms with those restricted to biogeography is still commonly used a situation which can be overcome by integrating data from different biota into a new palaeobiogeographic scheme herein a data set of 1809 species level taxa gastropoda and foraminifera serves as the base for interpretations gastropods in particular turned out to be of greatest value for the differentiation of palaeobiogeographic units due to sensitive reactions to all environmental parameters and occupying a wide range of ecological niches based on the excellent gastropod record the proto danubian province early danubian p danubian p balatonian p and a proto caspian subprovince are defined the biogeographic reorganisations are associated with five major biotic events within the gastropod faunas these big five comprise four extinctions the late ottnangian extinction event loee the mid badenian extinction event mbee the badenian sarmatian extinction event bsee the sarmatian pannonian extinction event spee and one exceptional immigration origination event termed the early badenian build up event ebbe foraminifera are less valuable for palaeobiogeographic purposes in the area and time slice studied endemisms are generally lower and turn over rates less dramatic they are however very useful for stratigraphic correlations with the mediterranean and atlantic areas this fairly well calibrated marine biostratigraphy of the central paratethys serves as stratigraphic backbone and control for continental stratigraphy

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

history of recurrent activity along a major fault in northeastern mexico mesozoic and tertiary faulting within a 280 km long west northwest trending zone in coahuila mexico is inferred from stratigraphic and structural evidence the fault forms the northern boundary of the late jurassic early cretaceous coahuila island uplift on the south during the jurassic and early cretaceous is indicated by a large detrital lithosome that formed on the northern side of the fault clast size within the early cretaceous part diminishes northward where the unit is divided into upper and lower parts by a limestone tongue these two early cretaceous detrital units plus two jurassic conglomerates at valle san marcos suggest episodic pre tertiary movement deformation of 242 2 m y old granites at valle san marcos also reflects several periods of pre tertiary movement uplift on the north along the same fault zone during the tertiary laramide raised permian and jurassic rocks into juxtaposition with cretaceous limestones extensive left lateral movement is neither proven nor precluded nevertheless because of the size orientation general location and times of movement of the fault we suggest that it may either be part of the megashear postulated by several authors for northern mexico or a splay of that megashear

rapid early holocene deglaciation of the laurentide ice sheet the demise of the laurentide ice sheet during the early holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the northern hemisphere and thus allows an assessment of rates of ice sheet decay as well as attendant contributions to sea level rise here we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the laurentide ice sheet when melting ice contributed about 1 3 and 0 7cm of sea level rise per year respectively our simulations with a fully coupled ocean atmosphere model suggest that increased ablation due to enhanced early holocene boreal summer insolation was the predominant cause of laurentide ice sheet retreat although the surface radiative forcing in boreal summer during the early holocene is twice as large as the greenhouse gas forcing expected by the year 2100 the associated increase in summer surface air temperatures is very similar we conclude that our geologic evidence for a rapid retreat of the laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the greenland ice sheet over the coming century

genesis stability and preservation potential of large lateral moraines of alpine valley glaciers towards a unifying theory based on findelengletscher switzerland abstract lateral moraines are prominent features of glaciated landscapes in high mountain environments and key landforms in glacier and palaeoclimatic reconstructions yet compared to smaller moraines they have been little studied and several aspects are not well understood we here present detailed sedimentological results from the lateral moraines of findelengletscher in sw switzerland to gain new insights into the formation of these landforms the lateral moraines studied here stand up to 140 m above the valley floor are over 3 km long and strongly asymmetrical in cross profile with distal slopes between 29 and 36 and proximal slopes that are commonly 41 64 but locally reach angles of up to 80 recorded lithofacies comprise loose clast and matrix supported stratified diamicts and intercalated sorted sediments in the distal slopes and near the crestline overconsolidated matrix supported massive and weakly stratified diamicts and streaked out sorted sediment lenses in the core and proximal slopes and partly intercalated dark brown layers overlain by loose and consolidated diamicts exposed in near vertical walls in the proximal flank these are interpreted as supraglacial debris flow units with intercalated fluvial wash horizons glaciotectonised and subglacial traction till with boudinaged and streaked out sediment lenses and palaeosoils overlain by sediment produced by overtopping of the former moraine surface during a subsequent advance of the glacier clast shape analysis and process observations reveal that the dominant mode of transport is subglacial and glaciofluvial and that the main mode of sediment delivery to the moraines is by debris flows after the material has been transferred from the bed via englacial debris bands and meltout at the surface this differs from previous studies that found that a supraglacial source was dominant sedimentary structures clast fabric and process observations during the 1979 1980 readvance of findelengletscher strongly suggest that proximal layers of reworked pre existing sediments and or basal traction zone till have been plastered onto the moraine core in several locations causing a high degree of overconsolidation and strongly clustered fabric eigenvalues s 1 0 94 with clustering parallel to the moraine crestline this suggests that a combination of basal lateral drag and lateral plastering produces the observed proximal stability and ensures a high preservation potential we develop a conceptual model that describes alpine lateral moraines as structurally complex landforms that do not just record a single event as often surmised and we discuss implications for palaeo glacier reconstruction and the application of numerical dating methods

cave sedimentation in the new guinea highlands this paper investigates the nature and processes of sedimentation of allogenic cave deposits in the high relief everwet karsts of montane new guinea under the high intensity rainfall regime episodic mass movements in small karst catchments provide a wide range of sediment textures from clayey gravels to fine clays these allogenic sediments are deposited into pools of water within the caves giving sedimentary structures analogous to turbidites diamictons within the cave relate to episodic mudflows in the catchment these deposits move as fluidized masses in a manner similar to some esker deposits cross stratified sediments are formed by dumping of pulses of sediment laden water into deep pools extremely fine grained clays and muds accrete parallel to underlying surfaces following flood pulses these deposits represent the last phase of catchment instability when a small amount of slopewash occurs catchment processes are dominated by solution and episodic mass movements when the thick root mat which masks the ground is disrupted some slopewash occurs but it is not a major component in catchment processes

upper bathyal trace fossils document palaeoclimate changes introductionichnofossils are good indicators ofenvironmental conditions in the geo logical past especially in the marinerealm bromley 1996 the oxygencontent and food availability areimportant for the burrowing organ isms and their uctuations in uencevertical distribution of trace fossilsalong sedimentary pro les savrdaand bottjer 1986 1994 wetzel anduchman 1998 2001 savrda 2007 bottom conditions in the oceans arein uenced by the climate trace fossils fig 1 exceedingly preserve informa tion about environmental conditionsat the time when they were produced but trace fossils of burrowing organ isms re ect environmental conditionsat a younger time compared with thehorizon where the burrows occur thetime interval burrowed by a de nedtrace fossil producer thus depends onthe sedimentation rate and penetra tion depth of the burrower with respect to the usefulness oftrace fossils for interpreting marinepalaeoenvironments the questionarises about the in uence of thepalaeoclimate on deep water tracefossil assemblages and how theseassemblages preserve this signal thisidea was already applied to latecretaceous erba and premoli silva 1994 savrda 1995 and eocene sed iments heard et al 2008 ndingcorrelations of trace fossils with orbi tal cycles stratigraphical andpalaeoenvironmental frameworka 102 m long section of predomi nantly middle miocene langhian sediments from a core in the southernvienna basin austria geographicalcoordinates utm wgs84 e016 13 44 n47 59 24 was investi gated using a multidisciplinaryapproach leading to the reconstruc tion of palaeoenvironmental condi tions ba ldi and hohenegger 2008 c oric and hohenegger 2008 hohe negger et al 2008b pervesler et al 2008 rupp and hohenegger 2008 wagreich et al 2008 according tothese investigations the sediments ofthis section represent sea oor condi tions of the upper bathyal in thewestern part of the paratethys sea harzhauser and piller 2007 pilleret al 2007 during the early middlemiocene the sedimentary successionconsists of more than 95 bioturbat ed marly shales wagreich et al 2008 whereby the upper part 6 40 m is condensed by tectonic distur bance hohenegger et al 2008a thedeeper section 40 102 m shows con tinuous sedimentation fig 2 thewhole section can be astronomicallytuned from 14 379 to 14 142 ma ago fig 2 based on the strong coinci dence of periods in anisotropicmagnetic susceptibility ams the calcium carbonate and organiccarbon content measured in the lower tectonically undisturbed section andon the correlation of these periodswith orbital cycles this dating ho henegger et al 2008a b is con rmedby the biostratigraphic tie points or bulina suturalis and the lack of heli cosphaera waltrans abdul aziz et al 2008 the average sedimentation rateis 470 mm ka

the new north american varve chronology a precise record of southeastern laurentide ice sheet deglaciation and climate 18 2 12 5 kyr bp and correlations with greenland ice core records new glacial varve records from long cores combined with records from key surface exposures and new radiocarbon ages have allowed the correction consolidation expansion and calibration of ernst antevs9 original new england varve chronology nevc in the connecticut valley of new england u s a the varve records have been reformulated with corrections and a new numbering system as the new north american varve chronology navc which is a continuous 5659 yr varve sequence that spans most of the last deglaciation 18 200 12 500 yr bp in the northeastern united states rates of ice recession for separate intervals terminated by abrupt glacial stillstands and readvances have been determined for western new england ice recession history is coupled to varve thickness changes that depict changes in meltwater production in the connecticut valley and show the relationship of changes in ablation rate summer climate variation to glacial readvances and periods of halted and rapid ice recession up to 300 m yr comparison of varve thickness records to greenland ice core climate records show that after 15 000 yr bp climate changes of sub century and longer scales recorded in both records appear identical and synchronous after 15 000 yr bp therefore there was a link between north atlantic climate and marginal processes of the southeastern sector of the laurentide ice sheet lis prior to 15 000 yr bp when the lis was closer to an equilibrium condition retreat rates were generally lower and changes in varve thickness and ablation were more subtle but can still be linked to ice sheet activity only weak relationships between varve thickness changes and greenland climate are evident suggesting that changes in the southeastern lis during this time may have been significantly influenced by climate patterns unique to the north american continent or ice dynamics

climatically influenced interactions between the mediterranean and the paratethys during the tortonian 1 the paratethys was a separate branch of the tethys ocean that developed as a series of inland seaways brackish lakes and wetlands within the interiors of central eastern europe and western asia during the oligocene neogene a short lived connection between the mediterranean sea and the paratethys continental realm toward the very end of the messinian salinity crisis is documented on the basis of the paratethyan affinity of the brackish shallow water faunas in several mediterranean localities nevertheless there are at present only a few comparative studies on stratigraphy paleobiogeography and paleoceanography of these two contiguous neogene provinces e g benson 2000 in this study we compare and integrate different stratigraphic data sets from middle upper miocene sequences of the central mediterranean and the western pannonian basins central paratethys that are seen as parts of a complex paleoclimatic and paleoceanographic system on the basis of this comparison we propose that the paratethys had a long lived influence on the large scale oceanographic circulation of the eastern mediterranean at least since the tortonian between 9 7 and 7 5 ma that is well before the onset of the messinian lagomare event 5 5 ma the integrated stratigraphy of coeval marine tortonian and continental transdanubian strata presented here suggests that mutual interaction and interdependence of climate subsystems ostensibly developed over the mediterranean area and central eastern europe continent and were orbitally forced long eccentricity insolation forcing is hypothesized to have exerted a broad control on the freshwater budget of the brackish pannonian basin and the consequent oceanographic setting of the mediterranean region

the ivaň canyon a large miocene canyon in the alpine carpathian foredeep abstract during the latest early miocene a large drainage system developed in the alpine carpathian foreland transporting sediments through a prominent submarine canyon along the narrow corridor between the south eastern bohemian massif and the waschberg danice unit the canyon followed the alpine carpathian foredeep from lower austria towards the north and northeast into the czech republic 3 d seismic data allow the mapping of this 600 m deep structure over a distance of 25 km and a width of 5 km despite its dimension making it the largest submarine erosive and sedimentary structure of the neogene alpine carpathian foredeep this canyon has not been previously recognised herein it is interpreted as shelf indenting canyon that formed due to a combination of isostatic rebound along a terminating thrust front and sea level change during the terminal early miocene the canyon fill comprises reworked littoral deposits with a typical early miocene tropical micro and macrofauna the exact timing of this refilling remains unclear smaller channel structures in surface outcrops representing potential tributaries of the canyon suggest a more or less synsedimentary filling soon after indention finally the top part of the canyon was eroded around the early middle miocene boundary probably related to a global 3rd order sea level drop and caped by marine marls during the subsequent early middle miocene transgression with the sudden onset of the subsidence of the northern vienna basin during that time the drainage system abruptly moved southward shedding its sediments into the newly opening vienna basin this explains the rather abrupt abandonment of the huge canyon feature whose fan deposits are unknown so far

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

high resolution calcareous nannoplankton palaeoecology as a proxy for small scale environmental changes in the early miocene within a 5 5 m thick succession of upper burdigalian cnp zone nn4 shallow neritic sediments from the north alpine foreland basin in lower austria a high resolution section of finely laminated sediment with a thickness of 940 5 mm was logged the section was continuously sampled resulting in 100 samples covering a thickness of 10 mm each an integrated approach was applied to these samples in order to study proxy records including calcareous nannoplankton geochemical and geophysical data multivariate statistics on the autochthonous assemblage were used to evaluate the ecological preferences of each taxon and to rule out possible contamination of the signal by taphonomic processes in order to assess changes in the assemblage composition throughout the section three taphogroups were defined using both the autochthonous and allochthonous nannofossils based on the distribution of these taphogroups five distinct intervals were defined that are indicative of centennial to decadal changes in palaeoenvironmental conditions combining these results with other proxies geochemistry geophysics we were able to reconstruct short term small scale variations in terms of temperature primary productivity bottom water oxygenation organic matter flux freshwater influx and changes in relative sea level in a highly dynamic shallow marine setting this study represents the first such high resolution analysis performed on a marine succession of late burdigalian age it is also a first attempt to analyse outcrop data on such a high resolution sub milankovitch scale with respect to calcareous nannoplankton in conjunction with geochemical and sedimentological data

thermoluminescence chronology of toronto area quaternary sediments and implications for the extent of the midcontinent ice sheet s we report direct dating by thermoluminescence tl methods of key quaternary stratigraphic horizons in the toronto area tl ages indicate that 1 most of the exposed sediments of the don formation at the sampled site were probably deposited during the closing phase of the sangamon interglacial 80 ka oxygen isotope stage 5a not the climatic optimum substage 5e 120 130 ka as generally supposed 2 overlying deltaic strata of the scarborough formation which accumulated in an ice dammed ancestral lake ontario were deposited between 60 and 50 ka early wisconsin oxygen isotope stage 4 3 the sunnybrook diamict overlying the scarborough formation was deposited in the middle wisconsin at 40 45 ka oxygen isotope stage 3 likely by glaciolacustrine processes rather than before 65 ka as previously supposed 4 sediments of the upper thorncliffe formation lying stratigraphically just beneath the last glacial maximum hallton till were deposited at 23 ka consistent with reliable 14 c dating thus the earliest wisconsin incursion of the proto laurentide ice sheet into the lake ontario basin as recorded by the scarborough formation probably did not take place until at least 60 ka and did not extend south and southwest of the toronto area until after 25 ka ice free conditions probably persisted over large areas of midcontinent north america from the end of the illinoian glaciation at 130 ka to the late wisconsin glacial maximum at 20 ka

astronomically forced teleconnection between paratethyan and mediterranean sediments during the middle and late miocene abstract a high resolution correlation between an orbital tuned middle and early late miocene record of the central paratethys and an astronomically calibrated mediterranean deep marine composite record is proposed the astronomical tuning of the sarmatian and pannonian sedimentary record in the vienna basin confirms that the beginning of the pannonian regional stage lower tortonian dated in this work at 11 42 my is very close to the miller event mi5 it coincides with a period of minimum amplitude in the 1 2 myr obliquity cycle which in the mediterranean marine record corresponds with a drastic change in the planktonic foraminiferal fauna in addition the warmer period between mi5 and mi6 corresponding to a maximum in the long term 2 3 myr eccentricity cycle coincides with a long interval of lignite deposition in the paratethyan realm the sedimentation pattern shown by high frequency cyclicity between lignite and normal sediments reflects a primary influence of 100 kyr eccentricity cycles on the sedimentation system of the central paratethys which corresponds with small and large scale sapropel clusters hierarchical organization in the mediterranean record the badenian sarmatian boundary astronomically dated at 13 32 myr does not coincide with a low amplitude variation in the 1 2 myr obliquity cycle and any mi events this orbital configuration is supported by the paleoclimatic and paleoecologic data of the late badenian and early sarmatian which both represent a warm temperate system with stagnant bottom water conditions finally the transitional phase from a temperate early sarmatian to a warmer late sarmatian associated with predominant carbonate sedimentation coincides with the glacio eustatic isotope event mi4 while the entire late sarmatian spans a complete 1 2 myr obliquity cycle

probability of moraine survival in a succession of glacial advances emplacement of glacial moraines normally results in obliteration of any older moraines deposited by less extensive glacial advances a process we call obliterative overlap a probability analysis of the likely impact of obliterative overlap on the completeness of the glacial record assumes that moraines were deposited at various distances from their glacial source areas randomly over time assuming randomness and obliterative overlap after 10 glacial episodes the most likely number of surviving moraines is only three the record of the pleistocene is in agreement with the probability analysis the 10 glaciations during the past 0 9 m y inferred from the deep sea record resulted in moraine sequences in which only two or three different aged moraine belts can generally be distinguished

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

lacustrine sediments in porter cave central indiana usa and possible relation to laurentide ice sheet marginal positions in the middle and late wisconsinan abstract proglacial lakes formed in the late quaternary with the advance of the laurentide ice sheet into mill creek valley of central indiana these lakes backfilled into the mouth of porter cave deposited organic matter and thinly bedded silty sediment that conforms to the underlying cave floor and shelves optical and radiocarbon ages indicate that deposition of fine grained sediments into porter cave occurred in two proglacial lake phases during marine oxygen isotope stage mis 3 ca 40 to 30 cal ka and mis 2 ca 27 to 18 cal ka the latter phase is consistent with other proxy evidence for ice sheet extent and timing we contend that the ice sheet lobe that dammed a proglacial lake during mis 3 in central indiana was 7 km behind the last glacial maximum limit based on current topography this conclusion is in opposition to previous assessments which infer ice free conditions in central illinois and central indiana ca 130 to 25 ka the paucity of mis 3 deposits may be due to erosion by the more extensive mis 2 ice sheet with glacial lacustrine sediments preserved in the protective confines of porter cave this outlet lobe in central indiana may be short lived and reflects a variable response of lobes of the laurentide ice sheet during mis 3 with expansion possibly associated with cooling during heinrich event 4

constraints on miocene oceanography and climate in the western and central paratethys o sr and nd isotope compositions of marine fish and mammal remains abstract the paratethys evolved as a marginal sea during the alpine himalayan orogeny in the oligo miocene sediments from the northern alpine molasse basin the vienna and the pannonian basins located in the western and central part of the paratethys thus provide unique information on regional changes in climate and oceanography during a period of active alpine uplift oxygen isotope compositions of well preserved phosphatic fossils recovered from the sediments support deposition under sub tropical to warm temperate climate with water temperatures of 14 to 28 c for the miocene 18o values of fossil shark teeth are similar to those reported for other miocene marine sections and using the best available estimates of their biostratigraphic age show a variation until the end of the badenian similar to that reported for composite global record the 87sr 86sr isotope ratios of the fossils follow the global miocene seawater trend albeit with a much larger scatter the deviations of 87sr 86sr in the samples from the well constrained seawater curve are interpreted as due to local input of terrestrially derived sr contribution of local sources is also reflected in the end values consistent with input from ancient crystalline rocks e g bohemian massif and or mesozoic sediments with end 7 excluding samples showing local influence on the water column an average end value of 7 9 0 5 may be inferred for the miocene paratethys this value is indistinguishable from the end value of the contemporaneous indian ocean supporting a dominant role of this ocean in the western and central paratethys

the beginning development and termination of the middle miocene badenian salinity crisis in central paratethys abstract middle miocene badenian evaporites of the carpathian region are underlain and overlain by deep water deposits the onset of evaporite deposition was sudden but not synchronous in all facies zones and the deposition of evaporites was controlled by the evolution of carpathian orogen in the carpathian foredeep and most probably in other basins the badenian evaporites represent the lower part of the nn6 zone halite and associated deposits in the central part of the badenian evaporite basin show the same facies successions and marker beds can be traced across and between individual basins characteristic marker beds made it possible to correlate various facies zones of the marginal ca sulfate platform these marker beds seem to reflect events that may be related to sudden and widespread changes in water chemistry which in turn imply major changes in basin hydrology the onset of the evaporitic deposition in the carpathian foredeep was clearly diachronous and the evaporites deposited in the basin centre preceded the beginning of evaporite sedimentation in the marginal basin however depositional history in the marginal basin and the basin centre was the same a general transgressive sequence of evaporites found in the carpathian foredeep resulted from the migration of facies zones induced by the nappe movement isotopic studies of badenian foraminifers occurring below evaporites suggest that the interrupted communication of the paratethys with the ocean was a consequence of eustatic sea level fall possibly related to climatic cooling and it was coupled with a tectonic closure of connection with the tethys thus both tectonics and eustacy have contributed to the origin of salinity crisis sedimentological and geochemical data indicate recycling of evaporites throughout most of the evaporite deposition the recycling at the end of gypsum deposition in the marginal sulfate platform was accompanied by a change in the hydrology of the central paratethys that was tectonically driven and possibly related to the block tectonic phase manifested in the marginal part of the carpathian foredeep basin the change in hydrology implied the dilution of brines by inflowing marine water and this terminated the middle miocene badenian salinity crisis the onset of the badenian salinity crisis shows great similarities to the onset of the messinian salinity crisis and the terminations of both crises were different

cyclostratigraphic dating in the lower badenian middle miocene of the vienna basin austria the baden sooss core the scientific borehole baden sooss penetrates a succession of badenian langhian middle miocene sediments at the type locality of the badenian the old brickyard baden sooss in the vienna basin the sedimentary succession of the 102 m cored interval consists of more than 95 bioturbated medium to dark gray marly shales with carbonate contents between 11 and 25 and organic carbon contents between 0 35 and 0 65 biostratigraphic investigations on foraminifera mainly lower part of upper lagenid zone and calcareous nannoplankton standard zone nn5 indicate an early badenian langhian age cycles in carbonate content organic carbon content and magnetic susceptibility have been identified by power spectra analysis correlations between the three variables are extremely significant using cross correlation periods around 40 m correlate significantly with the 100 kyr 1 eccentricity cycle the 20 m periods with the obliquity cycle and the 15 to 11 m periods with both precession cycles wavelet transformation and decomposition of composite periodic functions were used to obtain the position of the cycle peaks in the profile cross correlation with orbital cycles la2004 dates the baden sooss core between 14 379 1 and 14 142 my 9 kyr

tectono stratigraphic evolution of eastern mexico during the break up of pangea a review abstract the lower jurassic cenomanian successions of mexico can be grouped into two different tectono stratigraphic systems that were developed under the influence of two distinct geodynamic processes 1 the mesozoic atlantic system of mexico which occupies the eastern two thirds of the country and was dominantly influenced by the break up of pangea and consequent opening of the atlantic ocean and 2 the mesozoic pacific system of mexico which is exposed along its western margin and was controlled by the subduction of the farallon plate beneath the pacific margin of north america the mesozoic atlantic system of mexico can be subdivided into two tectono stratigraphic subsystems representing the two main tectonic stages of the break up of pangea the early middle jurassic rift subsystem was developed during the initial stage of lithospheric attenuation of western equatorial pangea which is evidenced by the opening of a number of right lateral transtensional troughs that were opened according to the nw se regional extension imposed by north america south america divergence rift related troughs were progressively infilled by continental to marginal marine deposits and locally by volcanic lava flows that display a geochemical signature typical of supra subduction settings based on these characteristics the rift subsystem is interpreted in this work as a hybrid tectono stratigraphic domain that displays characteristics that are typical both of the mesozoic atlantic system of mexico and mesozoic pacific system of mexico reflecting the superposition of the atlantic and pacific tectonic processes during the initial phase of north america south america divergence by late callovian time most of intra continental extension in western equatorial pangea had occurred and was followed by anticlockwise rotation of the yucatan block to its present position and initial seafloor spreading in the gulf of mexico the opening of the gulf of mexico promoted the incursion of marine waters in eastern mexico and the onset of carbonate basins and platforms that make up the late jurassic cenomanian drift and cooling subsystem the lack of arc like igneous rocks in the drift and cooling subsystem suggests that by the late callovian the mesozoic atlantic system of mexico was developed independently of the tectonic processes related to subduction along the pacific margin according to our synthesis the mesozoic atlantic system of mexico represents a unique stratigraphic record that was developed at least in part under the combined influence of two main tectonic processes that are 1 the divergence between north america and south america and 2 the subduction of the farallon plate in light of this the mesozoic atlantic system of mexico can be considered a natural laboratory to explore the evolution of complex geodynamic settings related to the interaction of plate tectonic boundaries

incipient axial collapse of the main cordillera and strain partitioning gradient between the central and patagonian andes lago laja chile 1 lago laja is a late quaternary volcanic dammed lake located near the drainage divide of the south central andes field observations lake reflection seismic profiles bathymetry and remote sensing data reveal an active fault system that runs parallel to the volcanic arc along the axis of the main cordillera the lago laja fault system llfs normal faults of this extensional system cut late pleistocene volcanics 2 7 mm yr since 7 1 ka the llfs accounts for 0 7 of arc normal extension at an average minimum rate of 1 2 mm yr and strain rate of 10 14 s 1 seismites and surface ruptures evidence m 6 paleoearthquakes the main cordillera at 37 s is a large scale pop up structure uplifted by thrusting along its foothills in this light we interpret extension in the axial and highest part of the andes as incipient synorogenic gravitational collapse in response to uplift and crustal thickening thermal weakening due to elevated heat flow and postglacial lithospheric rebound and unbending have probably contributed to the arc limited collapse and holocene acceleration of deformation rates the lack of significant strike slip offsets along the llfs as well as along both foothills thrust systems at 37 s contrasts with the intra arc dextral fault zone south of 38 s regional structural data indicates that north of 38 s diffusely distributed strain reflects low partitioning of oblique subduction while to the south deformation is localized in a discrete strike slip fault zone along the volcanic arc reflecting a higher degree of partitioning we relate this strain partitioning gradient to favorable fault orientations in the fore arc north of the arauco peninsula a major seismotectonic boundary

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

synextensional pliocene pleistocene eruptive activity in the camargo volcanic field chihuahua mexico the camargo volcanic field is the largest mafic alkalic volcanic field in the mexican basin and range province and the relationship between volcanism and normal faulting is especially strong the camargo volcanic field lies in the northern part of the province midway between the sierra madre occidental and trans pecos texas it is formed by pliocene pleistocene 4 7 0 09 ma intraplate mafic alkalic volcanic rocks some of which contain peridotite pyroxenite and granulite xenoliths the volcanic field covers 3000 km2 and has an estimated volume of 120 km3 erupted from 300 recognized vents twenty six new 40ar 39ar age determinations for the camargo volcanic field and its environs show that volcanic activity began in the southwest part of the field and shifted toward the northeast at 15 mm yr the average magmatic eruption rate during growth of the field was 0 026 km3 k y the camargo volcanic field lies within an accommodation zone with west dipping faults and east tilted blocks to the north and east dipping faults and west tilted blocks to the south these faults are expressed in the volcanic field by a n30 w trending graben with scarps up to 100 m high through its central part volcanism and faulting were at least in part coeval and younger volcanic products commonly drape fault scarps that cut earlier lavas normal faulting is bracketed between 4 7 and 2 1 ma and may have also migrated northeastward estimated vertical slip rates on four pliocene faults range from 0 03 mm yr a likely long term rate to 1 67 mm yr interpreted as a short term rate operative during periods of active faulting northwest striking normal faults that cut alluvial fan deposits and pleistocene lavas in the northern camargo volcanic field and geomorphic evidence for recent uplift to the south of the volcanic field suggest that the region is still extending

morphology of glacial striae implications for abrasion of glacier beds and fault surfaces glacial striae recently exposed on carbonate bedrock adjacent to saskatchewan glacier alberta provide information about the mechanics of abrasion beneath temperate glaciers and along fault surfaces the striae consist of plowed grooves that vary smoothly in width and depth but are located where similar variations in normal stress between the bed and subglacial rock fragments were unlikely finite element calculations of stresses in bedrock beneath abrading fragments suggest that under constant normal loading plowing elements with steep leading edges will plow progressively deeper into the bed with sliding whereas those with more gently inclined leading edges will climb out of their grooves results of simple experiments in which limestone slabs were pushed beneath fixed plowing elements indicate a similar dependence on contact geometry this dependence together with rotation of fragments during glacier sliding provides a plausible origin for the three characteristic shapes of striae in the area shapes of striae indicate that abrading fragments commonly rotate affecting depths of plowing and the shear stress supported by abrading debris an important refinement in models of glacial abrasion would be the incorporation of fragment rotations into estimates of abrasion rates and debris influenced glacier sliding velocities some striae become progressively deeper and wider down glacier and then end abruptly similar to some fault striae that have been linked to stick slip phenomena they may form as a result of tensile fracture at depth in front of plowing asperities that is not necessarily dependent on stick slip motion other minor structures along faults that are used as shear sense indicators may result from the same process

a series of large late wisconsinan meltwater floods through the champlain and hudson valleys new york state usa abstract the champlain valley in northeastern new york lies at the junction of two important late wisconsinan proglacial outflow routes the hudson valley to the south and the st lawrence valley to the northeast freshwater outflow from proglacial lakes in the hudson champlain valleys glacial lake albany vermont and the combined ontario and st lawrence valleys glacial lake iroquois may have affected ocean circulation and thereby altered climate during the last deglaciation we have estimated steady state and three flood pulse discharges from these large meltwater reservoirs into the north atlantic using channel geometry and a high resolution digital elevation model of the late wisconsinan paleogeography of the region we estimate the steady state meltwater discharge into the north atlantic to be 0 3 0 6 sv the first flood event was a combined iroquois vermont outflow at around 10 900 14 c yr bp that released 700 km 3 of meltwater into the north atlantic through the hudson valley with an estimated discharge of 1 1 sv a second outflow event released 2500 km 3 through the hudson valley shortly after the first event finally approximately 1500 km 3 was released to the north atlantic through the gulf of st lawrence at the incursion of the champlain sea about 150 300 years later

some fine grained sedimentation phenomena in caves fine grained sedimentation in caves often occurs by the parallel accretion of laminations upon the underlying bedforms these laminations show remarkable persistence in unit thickness and grain size in a down passage direction a translatory flow mechanism ofdeposition is postulated which results in the rhythmic pulsing of sediment laden water into subterranean lakes in response to variations in surface climate the sediments are pulsed into standing water via multiple inputs often resulting in coarser sediment being deposited on steeper slopes than on more gentle slopes the final extension of this sediment input is the complete filling of the cave passage to the roof the problem of sediment stability on steep slopes remains an unanswered anomaly

engineering geological properties of leitha limestone from historical quarries in burgenland and styria austria abstract this research has focused predominantly on assessing the most important physical and mechanical properties of leitha limestone rock samples and of a separate oolitic limestone sample in conjunction with sedimentological and microfacies analyses the microfacies characteristics of these samples together with their other technical properties help to explain why the leitha limestone is an important material for monuments and for restoration work rock samples for laboratory tests were collected from 12 sites located within alpine neogene basins samples for the assessment of rock properties were taken from abandoned quarries in the kaisersteinbruch bruckneudorf military area from abandoned and active quarries at st margarethen and from the aflenz underground quarry to broaden the scope of the investigations previous research results from quarries at st margarethen mannersdorf wolfsthal and hundsheim were also included thin sections were made from one of the drill cores from each quarry the microfacies analysis of the leitha limestone samples indicated a spectrum from encrusting coralline algae boundstones to coralline algae grainstones and rudstones and also included variable quantities of other bioclasts and siliciclasts the detailed results revealed considerable differences between the various samples which are considered to be from a shallow marine intertidal to subtidal paleoenvironment with variable hydrodynamic conditions the rock quality and durability were assessed through laboratory testing of physical and mechanical properties including measurements of real and apparent density porosity water absorption capacity uniaxial compressive strength ucs for both dry and water saturated rock samples and for samples following repeated freeze thaw cycles the coefficient of softening and the coefficient of freezing all investigated rock samples had different porosities and absorption capacities they also differed in their ucs values which were very variable but mostly belonged to the weak rock category ucs below 50 mpa five of the tested rock samples had higher ucs values and were consequently ranked in the firm rock category the microfacies investigation proved to be a valuable tool for interpreting the measured engineering geological properties in particular the porosity and rock strength

analysis of multiple cosmogenic nuclides constrains laurentide ice sheet history and process on mt mansfield vermont s highest peak abstract constraining glacial history and process on mt mansfield the highest peak in vermont 1339 m a s l provides insight into how the laurentide ice sheet shaped the underlying landscape when latest pleistocene ice retreated and how upland and lowland glacial histories relate here we quantify in situ cosmogenic 10be in 20 bedrock and boulder surfaces as well as in situ cosmogenic 14c in three of those surfaces to assess subglacial erosion and exposure history isotopic concentrations indicate that mt mansfield s lower elevations 400 1200 m a s l were deeply eroded by at least several meters during the last glaciation and then deglaciated rapidly 10be ages across this elevation span are indistinguishable and average 13 9 0 6 ka n 15 suggesting that 800 m of ice thinning occurred within at most about a millennium conversely the higher elevations 1200 m a s l preserve a more complex geomorphic history mt mansfield s summit surfaces contain 10be from previous periods of exposure indicating that the mountaintop landscapes were likely preserved beneath cold based weakly erosive glacial ice exposure ages from the shorter lived isotope 14c are younger 9 7 and 11 7 ka suggesting that mt mansfield s summit was covered until the early holocene perhaps by snowfields ice carapaces and or till our findings in context of previous work suggest that thinning laurentide ice flowed through the valleys for at most hundreds of years following deglaciation of the uplands but that the summit remained shielded by ice or sediment for millennia after the valleys became ice free

stratigraphic evidence of a pre wisconsinan interglaciation in the adirondack mountains new york abstract multiple tills separated by interbedded lake sediments were temporarily exposed during open pit mining at sanford hill near newcomb in the central adirondack mountains of northeastern new york radiocarbon ages of wood fragments from brown clay between two tills at that site indicate an age older than 55 000 yr b p a pollen profile in the brown pond clay tahawus clay records a transition from initial domination by pine spruce and birch to an oak pollen zone the upward disappearance of spruce and decrease of pine and birch are accompanied by diversification and increase in hardwood pollen this assemblage includes several warm climate hardwood species that are not represented in the postglacial flora of the region suggesting that the biota existed during an interglacial or interstadial interval that was warmer and or longer than postglacial time accordingly the tahawus clay is tentatively assigned to the sangamon interglaciation and probably to marine oxygen isotope substage 5e truncation of the tahawus clay by glacial erosion may account for the absence of a sangamon paleosol

long period orbital control on middle miocene global cooling integrated stratigraphy and astronomical tuning of the blue clay formation on malta 1 application of an astronomical age model to a bulk carbonate oxygen isotope record in the ras il pellegrin section on malta indicates that the major step in the middle miocene global cooling 13 82 ma 0 03 coincides with minimum eccentricity values associated with the 400 kyr cycle and minimum obliquity amplitudes associated with the 1 2 myr cycle this orbital configuration is very similar to that found for comparable oxygen isotope enrichment events in the late paleogene and neogene the stepwise character of the middle miocene cooling event appears to be controlled by the combined influence of the 100 kyr eccentricity cycle and the 172 kyr cycle in obliquity amplitude the integrated stratigraphy further allows extension of the astronomical polarity timescale to the top of chron c5acn the boundary between the globigerina limestone and the blue clay formation coincides with the major step in middle miocene global cooling and provides a level suitable for placing the physical reference point for the langhian serravallian boundary

orbitally paced climate evolution during the middle miocene monterey carbon isotope excursion one of the most enigmatic features of cenozoic long term climate evolution is the long lasting positive carbon isotope excursion or monterey excursion which started during a period of global warmth after 16 9 ma and ended at similar to 13 5 ma approximately 400 kyr after major expansion of the antarctic ice sheet we present high resolution 1 9 kyr astronomically tuned climate proxy records in two complete sedimentary successions from the northwestern and southeastern pacific odp sites 1146 and 1237 which shed new light on the middle miocene carbon isotope excursion and associated climatic transition over the interval 17 1 12 7 ma we recog nize three distinct climate phases with different imprints of orbital variations into the climatic signals 1146 and 123 7 delta 18 o delta 13 c 1237 xrt fe fraction 63 pm 1 climate optimum prior to 14 7 ma characterized by minimum ice volume and prominent 100 and 400 kyr variability 2 long term cooling from 14 7 to 13 9 ma principally driven by obliquity and culminating with rapid cryosphere expansion and global cooling at the onset of the last and most pronounced delta 13 c increase 3 icehouse mode after 13 9 ma with distinct 100 kyr variability and improved ventilation of the deep pacific the monterey carbon isotope excursion 16 9 13 5 ma consists overall of nine 400 kyr cycles which show high coherence with the long eccentricity period superposed on these low frequency oscillations are high frequency variations 100 kyr which closely track the amplitude modulation of the short eccentricity period in contrast to delta 13 c the delta 18 o signal additionally shows significant power in the 41 kyr band and the 1 2 myr amplitude modulation of the obliquity cycle is clearly imprinted in the 1146 delta 18 o signal our results suggest that eccentricity was a prime pacemaker of middle miocene climate evolution through the modulation of long term carbon budgets and that obliquity paced changes in high latitude seasonality favored the transition into the icehouse climate c 2007 elsevier b v all rights reserved

impacts of orbital forcing and atmospheric carbon dioxide on miocene ice sheet expansion the processes causing the middle miocene global cooling which marked the earth s final transition into an icehouse climate about 13 9 million years ago myr ago 1 4 remain enigmatic tectonically driven circulation changes 5 6 and variations in atmospheric carbon dioxide levels 7 8 have been suggested as driving mechanisms but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult here we present high resolution climate proxy records covering the period from 14 7 to 12 7 million years ago from two complete sediment cores from the northwest and southeast subtropical pacific ocean using new chronologies through the correlation to the latest orbital model 9 we find relatively constant low summer insolation over antarctica coincident with declining atmospheric carbon dioxide levels at the time of antarctic ice sheet expansion and global cooling suggesting a causal link we surmise that the thermal isolation of antarctica played a role in providing sustained long term climatic boundary conditions propitious for ice sheet formation our data document that antarctic glaciation was rapid taking place within two obliquity cycles and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change