diagnostic features and field criteria in recognition of tectonic sedimentary and diapiric melanges in orogenic belts and exhumed subduction accretion complexes abstract multiple episodes of deformation during the tectonic evolution of orogenic belts and ancient subduction accretion complexes cause obfuscation of primary block in matrix fabric of melanges and thereby making the recognition of their tectonic sedimentary or diapiric origin difficult here we present a comprehensive overview and synthesis of a diverse set of field based stratigraphic and structural criteria which are at the base of geological mapping rules to differentiate between various melange types developed by disparate geological processes and mechanisms we first define the current concepts of melange and melange nomenclature and describe the most diagnostic features of tectonic sedimentary and diapiric melanges at different scales we discuss some of the main issues complicating the application of these diagnostic criteria such as i similarities between the block in matrix fabric of different melange types formed in partially lithified sediments at shallow structural levels ii transformation of fabric elements with increased depth due to tectonic reworking and recrystallization processes iii significance of exotic versus native blocks in melange matrix and iv age relationships between blocks and matrix in a melange we introduce two additional criteria in approaching these complexities and in recognizing different processes of polygenetic melanges formation in the field when primary diagnostic fabrics were reworked by multiple deformational events these new criteria are based on i the coherence between lithological compositions of melange components blocks and matrix and characteristics and tectonic evolution of the geodynamic setting of their formation tectonic environment criterion and ii specificity and kinematic coherence in the distribution of deformation between blocks and the matrix deformation criterion the discussed diagnostic criteria can be applied to all field based investigations of melanges and broken formations in orogenic belts and exhumed subduction accretion complexes around the world regardless of their location age and tectonic history

paleotectonic significance of the quartzite of the sauratown mountains window north carolina recent mapping within the metamorphic core of the southern appalachians has led to the identification of several internal basement massifs interpreted to be windows that expose parautochthonous basement beneath the main thrust sheet one such internal massif is exposed within the inner piedmont of north carolina by the sauratown mountain window and is overlain by a cover sequence of arkose schist and quartzite detailed examination of the primary cross stratification types preserved within the quartzite at pilot mountain indicates that deposition took place in several marine environments ranging from foreshore to inner shelf deposits of similar origin within the early cambrian north american passive margin sediments appear to thin west to east from 80 m at the chilhowee group type locality at chilhowee mountain 300 km west southwest of pilot mountain to 40 m within the unaka belt 150 km west of pilot mountain the quartzite at pilot mountain is more than 45 m thick and therefore does not appear to represent a distal part of this passive margin sequence alternatively two paleotectonic interpretations seem plausible 1 quartzites of the sauratown mountains window north carolina represent late proterozoic tallulah falls ashe formation equivalent deposition along a sea floor high associated with the rifted basement terrane during the rift phase prior to the opening of iapetus or 2 quartzites of the sauratown mountains window north carolina represent latest proterozoic to early cambrian chilhowee group time equivalent deposition on an isolated rifted continental fragment during the drift phase of the north american iapetus margin evolution

biomarker proxy shows potential for studying the entire quaternary arctic sea ice history recently a novel and promising biomarker proxy for reconstruction of arctic sea ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons ip25 so far ip25 records have been restricted to the last 150 kyr bp here we present a biomarker record from ocean drilling program odp site 912 going back to the pliocene pleistocene boundary and indicating that sea ice of variable extent occurred in the fram strait southern yermak plateau area at least since about 2 2 ma furthermore our data support the idea that a combination of ip25 and open water phytoplankton biomarker data pip25 index may give more reliable and quantitative estimates of past sea ice cover at least for the study area this study reveals that the novel ip25 pip25 biomarker approach has potential for semi quantitative paleo sea ice studies covering the entire quaternary and motivate to carry out further detailed high resolution research on odp iodp material using this proxy

laterally and vertically accreted tidal deposits in the upper proterozoic madina kouta basin southeastern senegal west africa abstract the association of laterally and vertically accreted tidal deposits characterizes part of the upper proterozoic epicontinental deposits of the west african platform these deposits consist of symmetric thickening up thinning up decimetre to metre thick units bounded by centimetre thick argillaceous layers containing mud cracks each unit comprises neap spring tidal bundles in progradational cross bedded sandstones bounded above and below by aggradational flat bedded sand silt alternations the units are interpreted as deposits resulting from migration of subaqueous dunes lateral accretion over mud flats vertical accretion in an intertidal zone the cyclic organization of the units although imperfect because of preservation potential of strata cannot be explained by the dune field migration alone a periodic variation in the tidal environment of unknown origin but of longer duration than neap spring cycles is suggested

insights into circum arctic sea ice variability from molecular geochemistry abstract geological records of past sea ice such as those contained in arctic marine sediments offer an opportunity to strengthen our understanding of long term sea ice variability provided unambiguous paleo sea ice proxies can be developed one such recently proposed proxy is ip25 a highly branched isoprenoid alkene biosynthesized exclusively by sea ice dwelling diatoms haslea spp which is well preserved in marine sediments and could be used to reconstruct past changes in spring sea ice extent however little is known about regional scale controls on ip25 production in sea ice limiting its wider applicability as a paleo sea ice proxy to address this issue we examined the distributions of ip25 and the marine productivity biomarkers dinosterol and brassicasterol in a suite of surface sediment samples distributed across the arctic we find a statistically significant logarithmic relationship between ip25 and spring sea ice cover in sediment samples from arctic and subarctic sites in the pacific n 96 r2 0 67 p

semi quantitative estimates of paleo arctic sea ice concentration based on source specific highly branched isoprenoid alkenes a further development of the pip25 index abstract previously reported concentration data for highly branched isoprenoid hbi alkenes and the sterol 24 methylcholesta 5 22e dien 3 ol brassicasterol or epi brassicasterol obtained from 45 barents sea surface sediments reflecting contrasting sea ice conditions have been combined together in the form of the pip 25 index with outcomes compared with recent mean decadal satellite derived spring and summer sea ice concentrations reasonably good positive linear relationships were found between pip 25 indices and spring sea ice concentration with the strongest correlation found when using a tri unsaturated hbi hbi iii as the open water counterpart to the sea ice biomarker ip 25 likely as a result of the greater sensitivity and selectivity of hbi iii to the neighbouring sea ice conditions compared to epi brassicasterol the quality of the linear fits between p iii ip 25 i e pip 25 based on hbi iii and spring sea ice concentration together with their respective spatial distributions were also far less dependent on the balance factor c than for p b ip 25 i e pip 25 based on epi brassicasterol which may have important positive consequences for down core semi quantitative sea ice reconstruction and when making comparisons between outcomes from different arctic regions or climatic epochs in contrast consistently weak linear relationships were observed between individual biomarkers and spring or summer sea ice concentration and between pip 25 values and summer sea ice concentration however we provide evidence that a lower limit threshold for p iii ip 25 might represent a useful qualitative proxy for the past occurrence of summer sea ice surface sediment biomarker data from other regions will be needed before the significance of our findings can be fully evaluated

identification of contrasting seasonal sea ice conditions during the younger dryas abstract a palaeo sea ice reconstruction for northern norway for the interval ca 13 8 7 2 cal ka bp has been performed using a combined organic geochemical proxy based study of a marine sediment core jm99 1200 obtained from andfjorden 69 15 95 n 16 25 09 e and the outcomes compared with a series of other palaeoclimate studies carried out previously within this study particular emphasis has been placed on the identification of the sea ice conditions during the younger dryas and the application of different biomarker based proxies to both identify and quantify seasonal sea ice conditions firstly the appearance of the specific sea ice diatom proxy ip 25 at ca 12 9 cal ka bp in the sedimentary record has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the younger dryas stadial the near continuous occurrence of ip 25 for the next ca 1400 yr demonstrates seasonal sea ice during this interval although variable abundances suggest that the recurrent conditions in the early mid younger dryas ca 12 9 11 9 cal ka bp changed significantly from stable to highly variable sea ice conditions at ca 11 9 cal ka bp and this instability in sea ice prevailed for the subsequent ca 400 yr during which an extremely short interval of permanent or near permanent sea ice was observed at ca 11 75 cal ka bp at ca 11 5 cal ka bp ip 25 disappeared from the record indicating ice free conditions that signified the beginning of the holocene the ip 25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate p b ip 25 data from which more quantitative measurements of sea ice were determined p b ip 25 data were consistent with consecutively seasonal then infrequent sea ice cover for the early mid and late younger dryas while further comparisons of the p b ip 25 data with the outcomes of previous correlations with modelled sea ice concentrations suggested that these intervals were characterised by ca 60 90 and ca 0 60 sea ice cover respectively both qualitative and quantitative sea ice records were also consistent with sea surface temperature and other palaeoclimate estimates derived previously from various other proxy studies the contrasting seasonal sea ice conditions during the younger dryas were further verified through a comparison of the concentrations of ip 25 with those of another highly branched isoprenoid hbi alkene that is di unsaturated and believed to also be produced by sea ice diatoms the ratio of the hbi diene to ip 25 termed dip 25 is believed to provide a useful indicator of stability or variability in sea ice conditions and complements the outcomes from the ip 25 and p b ip 25 index data the identification of contrasting seasonal sea ice conditions during the younger dryas will likely contribute to the debate regarding the climatic impacts that took place during this intriguing interval

quantitative measurement of the sea ice diatom biomarker ip25 and sterols in arctic sea ice and underlying sediments further considerations for palaeo sea ice reconstruction abstract the lipid content of sea ice samples collected in 2011 and 2012 from resolute passage in the canadian arctic archipelago was measured and compared with related samples obtained from the amundsen gulf in 2008 the highly branched isoprenoid hbi sea ice biomarker ip 25 was found in sea ice samples from each study consistent with its formation by diatoms during the spring bloom our analysis also revealed the occurrence of a number of sterols in arctic sea ice and these were rigorously identified and quantified for the first time concentrations of ip 25 and sterols exhibited some variability between sampling studies with somewhat higher values in samples from resolute in 2012 than for the other two datasets consistent with a general increase in biomass however major differences in biomarker concentration between sampling studies were not observed an estimate of the proportion of arctic sea ice diatoms that produce ip 25 ca 1 5 was obtained by comparison of the concentration of ip 25 in the samples with those in laboratory cultures of known hbi producing diatoms and cell enumeration in selected sea ice samples the estimate is similar to the proportion of haslea spp in the same samples providing further support to the suggestion that at least some species of the haslea genus may be responsible for the biosynthesis of ip 25 and related hbi diatom lipids in arctic sea ice and that ip 25 is made by a relatively small proportion of sea ice diatoms in contrast median sterol ip 25 values were all substantially higher than those in cultures of hbi producing diatoms suggesting that sterols are made by the majority of sea ice diatoms the sterol ip 25 ratio was quite variable between locations and samples likely as a result of differences in diatom assemblage however a comparison of individual and median sterol ip 25 values in sea ice with those from surface sediments from different arctic regions demonstrated that sterols from sea ice diatoms may in some cases have a significant impact on the sedimentary budget this should be considered carefully for quantitative estimates of palaeo sea ice reconstruction using methods such as the pip 25 index which are based on the relative concentrations of ip 25 and sterols in arctic marine sediment cores

sea ice variations in the central canadian arctic archipelago during the holocene abstract a sea ice record for barrow strait in the canadian arctic archipelago caa is presented for the interval 10 0 0 4 cal kyr bp this holocene record is based primarily on the occurrence of a sea ice biomarker chemical ip25 isolated from a marine sediment core obtained from barrow strait in 2005 a core chronology is based on 14c ams dating of mollusc shells obtained from ten horizons within the core the primary ip25 data are compared with complementary proxy data obtained from analysis of other organic biomarkers stable isotope composition of bulk organic matter benthic foraminifera particle size distributions and ratios of inorganic elements the combined proxy data show that the palaeo sea ice record can be grouped according to four intervals and these can be contextualised further with respect to the holocene thermal maximum htm spring sea ice occurrence was lowest during the early mid holocene 10 0 6 0 cal kyr bp and this was followed by a second phase 6 0 4 0 cal kyr bp where spring sea ice occurrence showed a small increase between 4 0 and 3 0 cal kyr bp spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the htm elevated spring sea ice occurrences continued from 3 0 to 0 4 cal kyr bp although they were more variable on shorter timescales within this fourth interval we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the mediaeval warm period and the little ice age respectively comparisons are made between our proxy data with those obtained from other palaeo climate and sea ice studies for the caa

complementary biomarker based methods for characterising arctic sea ice conditions a case study comparison between multivariate analysis and the pip 25 index abstract the discovery of ip25 as a qualitative biomarker proxy for arctic sea ice and subsequent introduction of the so called pip25 index for semi quantitative descriptions of sea ice conditions has significantly advanced our understanding of long term paleo arctic sea ice conditions over the past decade we investigated the potential for classification tree ct models to provide a further approach to paleo arctic sea ice reconstruction through analysis of a suite of highly branched isoprenoid hbi biomarkers in ca 200 surface sediments from the barents sea four ct models constructed using different hbi assemblages revealed ip25 and an hbi triene as the most appropriate classifiers of sea ice conditions achieving a 90 cross validated classification rate additionally lower model performance for locations in the marginal ice zone miz highlighted difficulties in characterisation of this climatically sensitive region ct model classification and semi quantitative pip25 derived estimates of spring sea ice concentration spsic for four downcore records from the region were consistent although agreement between proxy and satellite observational records was weaker for a core from the west svalbard margin likely due to the highly variable sea ice conditions the automatic selection of appropriate biomarkers for description of sea ice conditions quantitative model assessment and insensitivity to the c factor used in the calculation of the pip25 index are key attributes of the ct approach and we provide an initial comparative assessment between these potentially complementary methods the ct model should be capable of generating longer term temporal shifts in sea ice conditions for the climatically sensitive barents sea

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

structural evolution of a major appalachian salient recess junction consequences of oblique collisional convergence across a continental margin transform fault most orogenic belts exhibit broadly arcuate regional map view trends of structural patterns commonly the inflection between opposing curves recesses and salients is a transverse zone marking a linear array of along strike contrasts in regional structure and stratigraphy analysis of such transverse zones can provide insight into the processes affecting orogenic curvature curvature is especially distinctive along the west flank of the appalachians where the tightest salient recess juncture is a thinned skinned transverse zone in georgia separating the alabama recess and tennessee salient and extending entirely across the width of deformed laurentian cover rocks this zone s most notable feature is a large oblique hanging wall ramp within the frontal metamorphic allochthon formed during alleghanian collisional events the basal decollement steps several kilometers stratigraphically upward across this ramp from proterozoic basement and its overlying late proterozoic rift sequence tennessee salient southwestward into basal cambrian and younger rocks alabama recess this ramp resulted from oblique sinistral displacement of the allochthon against an earlier east facing dextral continental margin transform fault that initially separated adjacent rifted margins of opposite polarity differences in the distribution thickness and facies of units indicate that important variations in basin geometry existed across the curvature inflection before paleozoic deformation suggesting that the orogenic curvature in part results from an inherited basin architecture translation of the allochthon over the ramp caused deflection of the tectonic transport trajectory major cross folding and rotation of earlier structures associated out of plane deformation propagated outward across the foreland producing the array of thinned skinned transverse structures aligned into the transverse zone

evolution of the murphy synclinorium southern appalachian blue ridge usa abstract the western blue ridge allochthon of the southern appalachians is dominated by the 180 km long murphy synclinorium paired with anticlinoria to the northwest these are first generation northwest overturned doubly plunging large amplitude and wavelength 10 km isoclinal folds contemporaneous with peak neo acadian orogeny visian 335 345 ma regional metamorphism the synclinorium folds a regional unconformity separating neoproterozoic rift and lower paleozoic drift sequences from a younger successor basin sequence strain analysis of metaconglomerates from lithologic groups above and below the unconformity indicates coaxial low to moderate oblate to nearly plane strain in both groups the synclinorium evolved via nnw sse crustal shortening 32 combined with orthogonal nne ssw sub horizontal flow stretching 35 45 sub parallel to the developing fold axes differences in metamorphic grade and paleodepth 10 17 km of the exposed synclinorium had essentially no effect on strain magnitudes retrodeformation of the embedded regional unconformity reveals a very broad synclinal warping of the rift and drift facies units predating superposition of the murphy synclinorium suggesting tectonic inheritance in the latter structure s origin the earlier mild deformation is post early cambrian and may represent the only vestige of the dynamic effects of the middle ordovician taconic orogeny to be found in this region

the arctic sea ice biomarker ip25 a review of current understanding recommendations for future research and applications in palaeo sea ice reconstructions in recent years a novel proxy for the past occurrence of arctic sea ice has been proposed that is based on the variable marine sedimentary abundance of an organic geochemical lipid derived from sea ice diatoms in the spring this lipid termed ip25 ice proxy with 25 carbon atoms is a highly branched isoprenoid mono unsaturated alkene that appears to be sufficiently stable in sediments to permit meaningful palaeo sea ice reconstructions to be carried out over short to long term timescales since the first proposed use of ip25 as a proxy for palaeo sea ice by belt et al 2007 a number of laboratories have measured this biomarker in arctic sediments and it is anticipated that research activity in this area will increase further in the future the content of this review is divided into a number of sections firstly we describe the scientific basis for the ip25 proxy and its initial discovery in arctic sea ice sedimenting particles and sediments secondly we summarise the relatively few studies that have to date concentrated on examining the factors that influence the production and fate of ip25 and we identify some areas of future research that need to be addressed in order to improve our understanding of ip25 data obtained from sedimentary analyses what is clear at this stage however it that the presence of ip25 in arctic marine sediments appears to represent a proxy measure of past seasonal sea ice rather than permanent or multi year ice conditions thirdly we highlight the importance of rigorous analytical identification and quantification of ip25 especially if measurements of this biomarker are going to be used for quantitative sea ice reconstructions rather than qualitative analyses alone presence absence fourthly we review some recent attempts to make the interpretations of ip25 biomarker data more detailed and quantitative by combining sedimentary abundances with those of phytoplankton and other sea ice derived biomarkers thus the bases for the so called pip25 and dip25 indices are described together with an overview of potential limitations concluding that investigations into the use of these indices needs further research before their full potential can be realised in the final section we provide a summary of ip25 based palaeo sea ice reconstruction case studies performed to date these case studies cover different arctic regions and timescales spanning decades to tens of thousands of years

paleozoic age of the walden creek group ocoee supergroup in the western blue ridge southern appalachians implications for evolution of the appalachian margin of laurentia in the foothills of the great smoky mountains in tennessee low grade metamorphic rocks of the walden creek group ocoee supergroup contain a fossil assemblage composed of trilobites bryozoans ostracodes pelmatozoans algae and agglutinated foraminifers indicating a silurian or younger age the new paleontological data contradict older ideas on the neoproterozoic age of the walden creek group the walden creek group was not deposited in a continental rift basin preceding the opening of the iapetus ocean but possibly in a pull apart basin formed in a transtensional event during the acadian orogeny there is no field evidence indicating that the walden creek group is separated from the lower units of the ocoee supergroup by a basin wide unconformity and hiatus a tentative geodynamic model is presented for the ocoee supergroup basin the model is dependent on paleontological data indicating a paleozoic age for the walden creek group and concentrates on lithologic petrographic and basin characteristics the model allows for the possibility that the entire ocoee supergroup was deposited in a paleozoic transtensional basin

high resolution record of late glacial and deglacial sea ice changes in fram strait corroborates ice ocean interactions during abrupt climate shifts the transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar north atlantic knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern fram strait a key area for water mass exchange between the arctic ocean and the north atlantic for the past 30 ka bp this reconstruction is based on the distribution of the sea ice biomarker ip25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western svalbard during the late glacial 30 ka to 19 ka bp recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic and or atmospheric variability a long lasting perennial sea ice coverage in eastern fram strait persisted only at the very end of the last glacial maximum i e from 19 2 to 17 6 ka bp and was abruptly reduced at the onset of heinrich event 1 coincident with or possibly even inducing the collapse of the atlantic meridional overturning circulation amoc further maximum sea ice conditions prevailed during the younger dryas cooling event and support the assumption of an amoc reduction due to increased formation and export of arctic sea ice through fram strait a significant retreat of sea ice and sea surface warming are observed for the early holocene

reinterpretation of the greenbrier fault great smoky mountains new petrofabric constraints and implications for southern appalachian tectonics the greenbrier fault in the southern appalachian blue ridge was defined as a premetamorphic younger over older thrust fault with a minimum 23 km of displacement subsequent studies accepted the original interpretation and further proposed that the fault represents a taconian foreland style ramp flat system the sole evidence for a foreland fold and thrust belt in the southern appalachians new structural and petrofabric observations in the great smoky mountains region permit reassessment of the original interpretation all major foliations mylonitic s c fabric and shear band cleavage in phyllonites s tectonites in the foot wall steep disjunctive shear band cleavage in footwall and hanging wall crenulation cleavage and schistosity above garnet grade are postmetamorphic and have similar ne strike and se dip all foliations in the foot wall are overprinted within meters of the fault by the s c shear band cleavage this fabric represents the youngest deformation event observed and postdates prograde and retrograde mineral assemblages indicating postmetamorphic slip along the contact no premetamorphic fault fabrics are present along the fault even in the lowest grade rocks postmetamorphic foliations near the fault may be accounted for by differential slip during folding of hanging wall and foot wall lithologies due to competency contrasts reconstitution of snowbird footwall meta siltstones into a phyllitic s c tectonite correlates with similar lithologies and fabrics that define the footwall along strike and that yield carboniferous ages for noncoaxial shear deformation the evidence permits the alternative interpretation that the greenbrier is a faulted stratigraphic contact that does not require tens of kilometers of displacement or deposition in separate basins along the extending laurentian margin and does not represent a foreland ramp flat system the general lack of premetamorphic folds and foliations in ocoee metaclastic rocks i e relatively static taconic barrovian regional metamorphism correlates with the absence of regional deformation in the southern appalachian foreland at a time middle ordovician when central and northern appalachian taconic type fold and thrust belts developed postmetamorphic middle to late paleozoic shortening of the entire great smoky mountain basement cover sequence and folding and extrusion of the competent great smoky group rocks relative to the underlying snowbird group may have produced km scale offset along the fault

formation of high pressure metabasites in the southern appalachian blue ridge via taconic continental subduction beneath the laurentian margin 1 tectonic models that account for the occurrence of eclogite retrograde eclogite peridotite and migmatitic basement gneisses in the southern blue ridge invoke closure of a small ocean basin between the eastern blue ridge ebr and western blue ridge wbr in this obducted ophiolite model franciscan type eastward subduction of oceanic crust beneath the piedmont arc occurred prior to obduction of the arc onto the laurentian margin the discovery of kilometer scale eclogite bodies near the ebr wbr boundary are cited as evidence for obducted ophiolite accreted island arc models however thermobarometric estimates based on mineral chemistry from hp metabasites of the western central and eastern blue ridge indicate that eclogites and granulites are medium temperature type 550 900 c inconsistent with the obducted ophiolite model mid ocean ridge basalt subducted beneath continental margins and island arcs rarely reaches temperatures in excess of 550 c thermobarometric comparisons of the present study and a reexamination of deep seismic profiles from the blue ridge allow for a model of westward subduction of continental material beneath laurentia during the taconic orogeny that produced a megamelange now preserved in the central and eastern blue ridge tectonic provinces p t paths determined from blue ridge hp metabasites are similar to p t paths determined previously from caledonian and variscan eclogites thermobarometric similarities imply a common tectonic history of continental collision subduction of continental crust to depths of 50 65 km followed by rapid eduction

variability of sea ice conditions in the fram strait over the past 30 000 years sea ice is a critical component of the climate and oceanographic system in the north atlantic ocean a biomarker record reveals millennial scale and glacial interglacial fluctuations in sea ice coverage in the northernmost atlantic ocean over the past 30 000 years

baffin bay paleoenvironments in the lgm and hs1 resolving the ice shelf question abstract core hu2008029 12pc from the disko trough mouth fan on the central west greenland continental slope is used to test whether an ice shelf covered baffin bay during the last glacial maximum lgm and at the onset of the deglaciation we use benthic and planktic foraminiferal assemblages stable isotope analysis of planktic forams algal biomarkers ice rafted detritus ird lithofacies characteristics defined from ct scans and quantitative mineralogy to reconstruct paleoceanographic conditions sediment processes and sediment provenance the chronology is based on radiocarbon dates on planktic foraminifers using a r of 140 30 14 c years supplemented by the varying reservoir estimates of stern and lisiecki 2013 that provide an envelope of potential ages hu2008029 12pc is bioturbated throughout sediments between the core base at 11 3 m and 4 6 m lgm through hs1 comprise thin turbidites plumites and hemipelagic sediments with greenlandic provenance consistent with processes active at the greenland ice sheet margin grounded at or near the shelf edge abundance spikes of planktic forams coincide with elevated abundance of benthic forams in assemblages indicative of chilled atlantic water meltwater and intermittent marine productivity ird and ip 25 are rare in this interval but brassicasterol an indicator of marine productivity reaches and sustains low levels during the lgm these biological characteristics are consistent with a sea ice covered ocean experiencing periods of more open water such as leads or polynyas in the sea ice cover with chilled atlantic water at depth rather than full ice shelf cover they do not support the existence of a full baffin bay ice shelf cover extending from grounded ice on the davis strait initial ice retreat from the west greenland margin is manifested by a pronounced lithofacies shift to bioturbated diatomaceous mud with rare ird of greenlandic origin at 467 cm 16 2 cal ka bp r 140 yrs within hs1 a spike in foraminiferal abundance and ocean warmth indicator benthic forams precedes the initial ice retreat from the shelf edge at the end of hs1 ip 25 brassicasterol and benthic forams indicative of sea ice edge productivity increase indicating warming interstadial conditions within the bolling allerod interstadial a strong rise in ip 25 content and ird spikes rich in detrital carbonate from northern baffin bay indicate that northern baffin bay ice streams were retreating and provides evidence for increased open water advection of atlantic water in the west greenland current and formation of an ird belt along the w greenland margin

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

mapping recent sea ice conditions in the barents sea using the proxy biomarker ip25 implications for palaeo sea ice reconstructions abstract an analysis of the sea ice proxy ip 25 and the open water phytoplankton indicator brassicasterol has been carried out for 93 surface sediments collected from the barents sea and some additional data from previous studies have been included to augment the analysis further consistent with a specific and selective sea ice diatom origin for ip 25 this biomarker was identified in virtually all sediments from seasonally ice covered locations but was absent from the majority of sites beyond the maximum sea ice extent msie for the period 1983 2002 in contrast brassicasterol was detected in virtually all sediments from the region and concentrations were not at all associated with the msie instead more localised regions of brassicasterol concentrations were identified and these likely reflect different influences on production and deposition when the ip 25 and brassicasterol concentrations were combined together in the form of the previously proposed p b ip 25 index the aforementioned association between ip 25 occurrence and the msie was clarified further and in addition provided more detailed descriptions of sea ice cover in particular p b ip 25 data indicated seasonal sea ice or marginal ice zone conditions for the region of the barents sea within the msie according to previously defined p b ip 25 ranges we also amalgamated the biomarker data from the current study with those derived previously by muller et al 2011 and compared these larger datasets with satellite derived mean spring sea ice concentrations significantly although the correlation between the combined ip 25 concentration dataset with the satellite data was very similar to that reported previously by muller et al 2011 the corresponding correlation using the p b ip 25 values was poorer with the larger dataset and some possible reasons for this are discussed finally in a small number of cases ip 25 was identified in sediments somewhat distal from the msie and it is hypothesised that the occurrence of ip 25 in these sediments results from allochthonous input following sediment advection between shelf and trough environments this is the first reported example that provides evidence for the allochthonous input of ip 25 into marine sediments and it is recommended that this should be considered carefully when carrying out palaeo sea ice reconstructions based on the occurrence of this biomarker in the future

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

on the thermo mechanical evolution of continental lithosphere elastic thickness of continental lithosphere is modified by both mechanical thickening and thinning events and thermal evolution a simple thermo mechanical model can account for the processes of tectonic alteration and subsequent thermal reequilibration of lithospheric thermal structure mechanical thinning or thickening of the lithosphere directly affects its thickness and flexural rigidity after a tectonic event thermal reequilibration proceeds at a rate dependent upon the amount of thinning or thickening and total lithospheric thickness previous tectonic history and the heat flux at the base of the lithosphere heat flux at the base of the lithosphere is controlled by the efficiency of convective mantle heat delivery rapid heat delivery to the base of the lithosphere retards lithospheric thickening whereas slow conductive heat delivery allows lithospheric thickening at the maximum rate the relative importance of thermal effects to mechanical alterations of lithospheric elastic thickness depends on the time scale of concern very thin lithosphere undergoes rapid thermal evolution such that cooling between tectonic events significantly thickens the lithosphere for thick lithosphere conductive heat transport is so slow that only minor changes in thermal structure and no significant changes in elastic thickness take place between tectonic events model results with infinite stretching agree with observations of oceanic lithospheric thickness evolution showing a divergence from a cooling half space at about 70 m y model results also agree with independent estimates of continental thermal evolution in the absence of tectonic events on the longest time scales approaching the age of the earth thermal reequilibration is attained and any tectonic effects are overprinted the time scale at which the transition between mechanically and thermally dominated elastic thickness evolution occurs depends on the heat transport efficiency of the convecting mantle for high nusselt numbers thermal effects take longer to become important even for lower nusselt numbers mechanical effects still dominate on time scales of 108 years crustal radiogenic heat production reduces the equilibrium lithospheric thermal and elastic thickness it also introduces a dependence of equilibrium thickness on tectonic crustal thinning or thickening model results indicate that on time scales of thrust sheet and sedimentary loading in foreland basins mechanical effects dominate the evolution of elastic thickness except for very thin lithosphere the model can be applied to the lithosphere beneath foreland basins so that observed basin geometry can be used to constrain tectonic history prior to loading by thrust sheets and basin sediments

deformation and metamorphic history of the western blue ridge eastern blue ridge terrane boundary southern appalachian orogen 1 the western eastern blue ridge boundary involved formation by premetamorphic thrusting of an oceanic fragment accretionary wedge island arc upon laurentian basement and metasedimentary cover detailed outcrop scale mapping structural and petrographic analysis reveal both terranes experienced the same deformation at the same metamorphic grade early f1 and f2 isoclinal folds are overprinted by f3 open to tight folds f3 transposes s2 to an axial planar cleavage s3 the youngest penetrative feature prekinematic to synkinematic relative to s2 barrovian metamorphism attained kyanite grade in the western blue ridge wbr upper amphibolite facies in the eastern blue ridge ebr and anatexis in both terranes postkinematic m2b is characterized by appearance of fibrolite throughout the kyanite zone coarsening to granular sillimanite and identification of a kyanite sillimanite isograd in the wbr d3 strain was accommodated by dynamic recrystallization of quartz neocrystallization folding and basal slip of micas pressure solution of plagioclase folding of kyanite and fracturing of garnet scattered lower greenschist facies m4 static retrograde metamorphism resulted in replacement of kyanite and garnet by sericite and chlorite respectively although the juxtaposition of two lithologically distinct terranes implies a fault relationship polymetamorphism and deformation obliterated any microfabrics mineral assemblages or structures that might have developed during premetamorphic thrusting the boundary cannot be an extension of a continent scale dextral strike slip fault system inferred to have developed along laurentian margin in the devonian

a biomarker based reconstruction of sea ice conditions for the barents sea in recent centuries variations in sea ice occurrence for the barents sea since c ad 1700 have been determined by analysis of the abundance of the sea ice biomarker ip25 in three marine sediment box cores obtained from locations in the north southeast and southwest parts of the region depth age models for each core were established using excess 210pb activity profiles comparisons between these depth age models with those reported previously for the barents sea suggest that the proxy sea ice record may alternatively extend back to c ad 1500 1600 sedimentation accumulation rates and bulk densities were combined with ip 25 concentrations resulting in temporal changes to ip25 fluxes which have been interpreted in terms of sea ice variability the ip25 sea ice proxy data are also compared with other bulk organic geochemical parameters total organic carbon and c n ratios and with sediment particle size distributions the data indicate ice free conditions for the southwest barents sea for the past c 300 yr consistent

towards quantitative sea ice reconstructions in the northern north atlantic a combined biomarker and numerical modelling approach article i nfo organic geochemical analyses of marine surface sediments from the continental margins of east greenland and west spitsbergen provide for a biomarker based estimate of recent sea ice conditions in the northern north atlantic by means of the sea ice proxy ip25 and phytoplankton derived biomarkers e g brassicasterol and dinosterol we reconstruct sea ice and sea surface conditions respectively the combination of ip25 with a phytoplankton marker in terms of a phytoplankton marker ip25 index pip25 proves highly valuable to properly interpret the sea ice proxy signal as an under or overestimation of sea ice coverage can be circumvented a comparison of this biomarker based assessment of the sea ice distribution in the study area with 1 modern remote sensing data and 2 numerical modelling results reveal a good agreement between organic geochemical satellite and modelling observations the reasonable simulation of modern sea ice conditions by means of a regional ocean sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area the good correlation between modelled sea ice parameters and the biomarker based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross evaluation this combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of ip25 future ip25 studies on marine surface sediments from the arctic realm however are recommended to extend and validate this new attempt of using ip25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions

paleozoic and grenvillian structures in the southern appalachians extended interpretation of seismic reflection data interpretive reprocessing of seismic reflection data has elucidated paleozoic and grenvillian structures in the southern appalachians the seismic data include a 7500 km grid of adcoh seisdata and cocorp reflection profiles that traverse the blue ridge and inner picdmont geologic provinces of north carolina south carolina and georgia surface geology and potential field data were used to constrain the interpretation the reprocessed seismic reflection data have delineated the internal and external geometry of the crystalline blue ridge inner piedmont allochthon including the locations of the blue ridge master decollement haycsville fault and brevard fault zone on the basis of the reprocessed data all of the major faults within the allochthonous upper crust sole in the blue ridge master decollement reflections extending to the southeast from beneath the surface location of the hayesville fault to the blue ridge thrust might be the seismic signature of a high strain zone this implies that internal deformation of the blue ridge allochthon associated with the alleghanian orogeny might have occurred farther to the west than has been previously documented from field studies relative amplitude seismic data enabled the discrimination between blue ridge inner piedmont crystalline rocks and underlying lower paleozoic shelf strata thereby delineating the blue ridge thrust the interpreted geometry constrains the top of the shelf sequence beneath the blue ridge to depths of less than 3 km this relatively shallow depth of the shelf strata together with the presence of duplex structures and bright spots that are imaged within the sequence might imply favorable conditions for hydrocarbon exploration beneath the blue ridge midcrustal reflections from within the upper to iower crust are interpreted to originate from preserved grenvillian structures that were reactivated at the basement surface during late proterozoic early cambrian extension reflection continuity is occasionally disrupted by interpreted post grenvillian pre early cambrian low density intrusions topography at the basement surface possibly caused by the intrusions is interpreted to have controlled the formation of some of the structures within the overlying allochthon including blue ridge and brevard fault zone ramps correlation of seismic time structure contour maps with available gravity data and two dimensional gravity modeling suggest that anomalies in the gravity field can be attributed to low density sources within the autochthonous crust discontinuous reflection packages from depths of 36 42 km are interpreted to originate from the mohorovi i discontinuity the reflectors trend about n15 e with a true dip of approximately 15 nw

identification and characterisation of a novel mono unsaturated highly branched isoprenoid hbi alkene in ancient arctic sediments abstract the occurrence of a novel c 25 highly branched isoprenoid hbi mono unsaturated hydrocarbon in arctic marine sediments from the fram strait is described the structure was determined following synthesis from a closely related diene and nmr spectroscopic analysis the position of the double bond was confirmed by oxidation ruo 4 and comparison of the mass spectrum of the resulting c 19 ketone with that of an authentic sample synthesised previously the same c 19 ketone was also present following oxidation of the fram strait sediment extracts the source of the novel hbi monoene biomarker is not known but is believed to be certain marine diatoms on the basis of structural similarities with other hbis from such sources it does not however appear to be biosynthesised by arctic sea ice diatoms unlike its regio isomer ip 25 an established proxy for arctic sea ice alternatively it may represent a diagenetic product of the sea ice diatom biomarker ip 25 this seems unlikely however on the basis of their respective structures since the new hbi monoene and ip 25 possess similar gas chromatographic and mass spectral properties but probably have contrasting sources we suggest that future paleo sea ice reconstruction studies based on the occurrence of ip 25 should pay further attention to the rigorous assignment of this biomarker in marine sediment extracts some suggestions for achieving this based on analytical purification and mass spectrometric measurements are provided

source specific biomarkers as proxies for arctic and antarctic sea ice abstract over the last decade or so certain source specific c25 highly branched isoprenoid hbi lipid biomarkers have emerged as useful proxies for arctic and antarctic sea ice thus ip25 ice proxy with 25 carbon atoms and ipso25 ice proxy for the southern ocean with 25 carbon atoms represent binary measures of past seasonal sea ice in the arctic and antarctic respectively a further tri unsaturated hbi generally referred to as hbi iii appears to provide proxy evidence for the region of open water found adjacent to sea ice i e the marginal ice zone miz in both polar regions this review provides an update on current knowledge pertaining to each proxy the first section focuses on describing those studies that have aimed to establish the underlying features of each proxy including source identification and spatial distribution characteristics the second section presents some important analytical considerations pertinent to the accurate identification and quantification of hbi biomarkers the third section describes how each hbi proxy is normally interpreted within the sedimentary record for palaeo sea ice reconstruction purposes this includes the interpretation of individual and combined biomarker profiles such as the pip25 index and multivariate decision tree models a summary of all previous palaeo sea ice reconstructions based on hbis is also given which includes examples that clarify or reinforce our understanding of the individual or combined biomarker signatures some knowledge gaps and areas for future research are also briefly described

characterization of fluvial deposits interbedded with flood basalts neoproterozoic catoctin formation central appalachians usa abstract the catoctin formation infills a neoproterozoic age rift basin associated with the development of the laurentian continental margin one of several similar basins that are distributed along the length of the southern to central appalachian basin the catoctin formation consists of a flood basalt sequence with intercalated sedimentary deposits two types of architectural elements channel element ce and sheet element se are recognized within these sedimentary deposits massive structureless sandstones and conglomerates are the dominant facies within the ce and se and are interpreted to record deposition from hyperconcentrated flows lack of vegetative binding of sediment coupled with a relatively high stream gradient and possibly a high water table enhanced the probability of developing hyperconcentrated flows by the process of bulking addition of sediment to a flow additional facies present are the products of normal stream flow that developed from waning hyperconcentrated flows basaltic effusive rate sediment supply and extension subsidence controlled the generation of ce and se all ce reflect deposition in isolated fluvial channels incised into lava flows and are present within the lower member of the catoctin formation the presence of ce most likely indicates a high rate of lava extrusion low sediment supply and possible high subsidence rates the se composing the sedimentary member of the catoctin formation reflects a decrease in effusive and subsidence rates and a increase in sediment supply from the hinterland overlying the se is the last phase of basin infill characterized by basalts with minor interbedded clastic rocks the final phase of infilling was effected by an increase of effusive and subsidence rates and a potential cutoff of sediment supply the catoctin formation basin displays a more complex infill history than generally associated with the rift deposits of the laurentian margin

abrupt climate changes for iceland during the last millennium evidence from high resolution sea ice reconstructions a high resolution account of icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker ip25 produced by sea ice algae comparison with historical sea ice records demonstrates a strong correlation between documented sea ice occurrences and the ip25 proxy an excellent agreement is also observed between the ip25 record and a diatom based sea surface temperature reconstruction obtained from the same core and the crowley and lowery northern hemisphere temperature reconstruction using this approach we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and or climate conditions around iceland during the little ice age

seasonal sea ice cover during the warm pliocene evidence from the iceland sea odp site 907 abstract sea ice is a critical component in the arctic and global climate system yet little is known about its extent and variability during past warm intervals such as the pliocene 5 33 2 58 ma here we present the first multi proxy ip25 sterols alkenones palynology sea ice reconstructions for the late pliocene iceland sea odp site 907 our interpretation of a seasonal sea ice cover with occasional ice free intervals between 3 50 3 00 ma is supported by reconstructed alkenone based summer sea surface temperatures as evidenced from brassicasterol and dinosterol primary productivity was low between 3 50 and 3 00 ma and the site experienced generally oligotrophic conditions the east greenland current and east icelandic current may have transported sea ice into the iceland sea and or brought cooler and fresher waters favoring local sea ice formation between 3 00 and 2 40 ma the iceland sea is mainly sea ice free but seasonal sea ice occurred between 2 81 and 2 74 ma sea ice extending into the iceland sea at this time may have acted as a positive feedback for the build up of the greenland ice sheet gis which underwent a major expansion 2 75 ma thereafter most likely a stable sea ice edge developed close to greenland possibly changing together with the expansion and retreat of the gis and affecting the productivity in the iceland sea