late quaternary cryostratigraphy of a coastal cliff at martha point southwest banks island western canadian arctic a 5 m thick unlithified sequence consisting of sands silts and minor peats crop out in a coastal cliff within continuous permafrost a well exposed 70 m long section displayed a range of epigenetic ice wedges these could be classified into three generations each at a different stratigraphic level the oldest was truncated by a major thaw unconformity which was overlain by a bed of highly involuted silts with peat clasts interpreted as evidence of a deep palaeoactive layer and associated thermokarst this bed forms part of a regionally extensive thermokarst phase correlated with an early holocene climatic optimum the other two ice wedge horizons postdate the thermokarst event with the youngest approximating to the base of the modern active layer

a model of coastal evolution in a transgressed thermokarst topography canadian beaufort sea abstract the coast of the southern canadian beaufort sea consists of bluffs of ice bearing quaternary sediments and of spits and barrier islands enclosing more or less completely lagoons and complex embayments formed by the breaching of thaw lakes the study of the evolution of this coast developed in a thermokarst topography and of the shallow stratigraphy of the inner continental shelf has resulted in the development of a conceptual model of coastal evolution five stages have been defined in this model which form an idealized continuum of coastal evolution according to the model the formation of embayments spits and barrier islands is primarily controlled by the pre existing topography relative sealevel rise and local sediment supply sealevel rise over a topography of thermokarst basins formed in ice bearing sediments leads to the formation of embayments and rapidly eroding headlands from which spits develop geomorphic evidence suggests that barrier islands mainly form by spit breaching or by erosion of tundra islands breached lake basins act as sediment sinks and may restrict the development of coastal accumulation features spits and barrier islands are rapidly retreating landward the mean retreat rates being 2 2 m a 1 and 3 9 m a 1 respectively on an annual time scale spits and barrier islands retreat in response to episodic storm generated overwash events but on a geologic time scale relative sealevel rise in the major forcing mechanism of landward migration while retreating landward these coastal accumulation features may be drowned and possibly partially preserved in breached lake basins during the holocene transgression the shoreface has undergone erosional retreat partly eroding the pre existing topography but preserving the bottom of some breached thaw lakes and lagoons which are now overlain by a transgressive sand sheet on the inner shelf our observations provide the basis of a semi quantitative model of shoreline changes for the barrier coast of the canadian beaufort sea which relates coastal stability to bluff erosion ground ice content sediment texture offshore sediment supply wave energy volume of breached lake basins relative sealevel rise and regional slope

major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america keuhn s c froese d g carrara p e foit jr f f pearce n j g rotheisler p 2009 major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america quaternary research 71 2 201 216 sponsorship nserc discovery grant alberta ingenuity new faculty award to duane froese

investigating the likelihood of a reservoir offset in the radiocarbon record for ancient egypt some radiocarbon dates for ancient egypt have been significantly offset from the established historical chronology see bonani et al 2001 in this paper short lived plant species collected in egypt between 1700 and 1900 ad were used to investigate the possibility that the radiocarbon record had been influenced by reservoir effects ams radiocarbon measurements were made on 66 known age samples resulting in an average offset from expected values of 19 years the implications of this minor discrepancy on the likelihood of a reservoir process are discussed and the agreement of the data with recent models of radiocarbon seasonality is also considered

radiocarbon dating reveals the timing of formation and development of pedogenic calcium carbonate concretions in central sudan during the holocene abstract calcic soil horizons are common in arid and semi arid lands and represent the result of the progressive accumulation of calcium carbonate in the soil profile over time this process leads to the occurrence of several pedogenic phases of calcium carbonate dissolution precipitation for this reason timing the formation and development of calcic horizons through radiometric dating is not straightforward as time averaging effects due to the superimposition of the same process over time occur on this basis this study aims to define the timing and dynamics of formation and development of pedogenic calcium carbonate concretions from semi arid central sudan highlighting the relevance of a multi disciplinary approach and the effectiveness of radiocarbon dating coupled to an accurate sampling strategy applied to pedogenic carbonates calcic soil horizons bk were sampled during the archaeological excavation of site 16 d 4 at al khiday central sudan and studied by optical cathodoluminescence and scanning electron microscopy as well as by chemical physical and stable isotopes c and o analyses micromorphological analyses reveal the occurrence of distinctive calcitic pedofeatures here described as calcitic cemented nodules and calcitic rich matrix radiocarbon ages obtained for these pedofeatures mostly refer to the early holocene for calcitic cemented nodules 11 5 9 9 and 9 6 cal ka and to the middle holocene for powdery calcitic rich matrix 7 9 7 7 6 3 and 6 1 cal ka samples additionally 13c and 18o values indicate major shifts of environmental conditions from the early to the middle holocene in agreement with the available information from detailed palaeoenvironmental studies carried out in the region in particular early holocene pedogenic calcitic features can be related to short arid phases during general wetter climate conditions whereas those formed in the middle holocene can be related to short humid phases results show that bk horizons were characterized by alternate periods of calcite accumulation precipitation and dissolution and periods of quiescence or extremely slow growth rates thus the formation and development of bk horizons have been a long lasting process significantly influenced by climatic fluctuations this study represents a further step in the comprehension of the development of calcium carbonate concretions and at a wider perspective calcrete the paper also contributes to the definition of a reliable method to radiometrically date the formation of calcic pedofeatures on a broader perspective this work may offer a significant tool for archaeometric studies where the interaction between secondary calcite and archaeological material is significant e g radiocarbon dating of bioapatite in bones and palaeoenvironmental studies in arid lands where bk horizon development is a function of past rainfall

attributes and evolution of an exhumed salt weld la popa basin northeastern mexico an elongate arcuate structure consisting of a fault like displacement surface previously regarded as a reverse fault and parallel synclines within the late cretaceous eocene la popa basin of northeastern mexico are herein reinterpreted as a salt weld and its flanking withdrawal synclines the structure resulted from hanging wall subsidence during evacuation of salt along a formerly diapiric salt wall the la popa weld has an exposed length of 25 km and superficially resembles a growth fault the displacement surface is convex to the southwest and dips south to southwest stratigraphic displacement at the surface is zero at either end and increases to 5 km halfway along the trace of the structure the la popa structure had a two phase history 1 a diapiric phase marked by rise of an elongate salt wall flanked by parallel withdrawal synclines and 2 a subsequent evacuation phase recorded by hanging wall subsidence and stratigraphic welding of footwall and hanging wall as salt evacuated from the former diapir during diapirism thick siliciclastic strata accumulated in the salt withdrawal synclines that formed by downbuilding adjacent to the rising salt wall siliciclastic units thinned toward the salt wall near which they were upturned and developed numerous angular unconformities thick biohermal carbonate lentils accumulated episodically on topographic highs associated with the rising salt wall evacuation of the salt wall caused lateral migration of the hanging wall synclinal hinge and a consequent shift of thickest synkinematic strata toward the developing weld this is the first exposed example of a secondary salt weld described as such in the literature

evaporite diapirs in the la popa basin nuevo leon mexico reconnaissance mapping and stratigraphic work in the la popa basin of nuevo leon northern mexico has revealed two large structural features with cores of gypsum and anhydrite at the surface these features are interpreted to be the surface expression of evaporite diapirs they are exposed in folded sedimentary rocks belonging to the potrerillos formation of the difunta group of maastrichtian age late cretaceous sandstone units within the potrerillos formation pinch out toward the piercement features carbonate lentils composed of rudistid reefs and associated carbonate clastics flank the features and pinch out away from the features into marine shale members of the potrerillos formation most carbonate lentils occur in the immediate vicinity of the evaporite features and are interpreted to be genetically related to the diapirs syndiapiric sedimentary facies patterns can be documented over 4 000 vertical feet 1 200 m of section within the potrerillos formation the large vertical extent of facies peculiarities near the piercement features indicates that the features were active for an extended period corresponding to at least two regressive transgressive cycles during maastrichtian time a radial drainage pattern away from the northern feature indicates that the features are probably active today a limestone inclusion from within one of the features has been dated as kimmeridgian in age zuloaga or smackover equivalent and suggests that the evaporites are probably derived from the jurassic minas viejas formation it is not known at present whether salt underlies the surface crust of gypsum and anhydrite at the time that the first syndiapiric sediments of the potrerillos formation were deposited the minas viejas formation was buried at an estimated depth of 17 000 ft 5 200 m the thick pre laramide cover the pre laramide age of at least some of the syndiapiric sedimentary features and the location of stocks away from major anticlines indicate that the emplacement of the diapirs is not related to laramide compression geostatic loading is considered to be the most important mechanism for emplacement of the domes

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

halokinetic sequences and diapiric structural kinematics in the field two day excursion to la popa basin northeastern mexico exposures of salt diapirs and flanking strata in la popa basin in the mexican states of nuevo leon and coahuila contain world class examples of salt sediment interaction that provided the basis for the concept of halokinetic sequences the basin also contains one of the first secondary salt welds described in outcrop the two day field trip described here provides an easily accessible overview of salt sediment relations within a short distance of monterrey the capital city of nuevo leon the first day constitutes an introduction to basin stratigraphy a traverse through halokinetic sequences at el papalote diapir and visits to the cretaceous paleogene boundary bed and a salt cored detachment fold near the town of hidalgo north of monterrey the second day is a visit to la popa salt weld where stops at several parts of the weld permit comparison of different structural styles developed along the weld the trip begins and ends at the marriott courtyard hotel near the monterrey airport

bayesian modelling of an absolute chronology for egypt s 18th dynasty by astrophysical and radiocarbon methods only a few astrophysical points and synchronisms listed in texts provide anchor points for the absolute chronology of ancient egypt at first we will show how we can re calculate some of these anchor points by using sothic dating based on the arcus visionis method and modelling lunar dates using a bayesian approach then we will discuss two radiocarbon studies carried out on short lived egyptian materials held at the louvre museum that could be attributed to particular reigns or other precise periods using a bayesian approach these dates were combined with the known order of succession and the lengths of reigns sothic and lunar dates were integrated as priors in the model this approach has led to a new proposal for the absolute chronology of egypt s 18th dynasty

halokinetic sequences in carbonate systems an example from the middle albian bakio breccias formation basque country spain in diapir flanks unconformity bounded sedimentary packages associated with gravity driven deposits controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences the bakio breccias formation basque country spain corresponds to redeposited carbonate deposit that developed in response to the bakio diapir growth during the middle albian these deposits provide on of the rare documented example of carbonate dominated halokinetic sequences the bakio breccias formation consists of an alternation of clast and matrix supported breccias calcirudite calcarenite and marl deposited along the flanks of the diapir the description and the analysis of the bakio breccias formation lead to a new model for carbonate dominated halokinetic sequences these sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs while sediments are preferentially deposited in the mini basins adjacent of the diapirs in siliciclastic settings during transgressive system tract carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs forming thick and resistant roof which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities wedge halokinetic sequences during late highstand system tract deposition and lowstand system tract if present platform progradation results in high sediment accumulation in the adjacent depocenters loading the autochthonous salt layer and promote diapir growth and creation of topographic relief in addition if the diapir roof reaches emersion karstification of the carbonate platform top may also favour roof destruction and diapir growth depending on the thickness of the roof developed previously and the amplitude of the sea level fall the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities hook halokinetic sequences furthermore gravity driven deposits are assumed to be more common in carbonate dominated halokinetic sequences compared to their siliciclastic counterparts since carbonate platform aggradation creates steep slopes on the diapir margins leading to the partial collapse of the margin even when limited diapir growth occurs the carbonate dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed

stratigraphic isotopic and mineralogical evidence for an early holocene thaw unconformity at mayo yukon territory ice rich glaciolacustrine sediments near mayo yukon territory reveal a thaw unconformity in the form of truncated ice wedges and abrupt changes in cryotexture the unconformity has been radiocarbon dated at 8870 200 years bp which is within the holocene period of optimal climatic conditions in northern yukon and the mackenzie delta area reported by other workers analysis of the mineralogy of the sediments indicates that the material above the unconformity is enriched in minerals that are the products of a more intense weathering environment than those deeper in the profile oxygen isotope ratios of ground ice in the sediments suggest the presence of two genetically distinct ice units above and below the unconformity an average rate of upward permafrost growth in this area of 0 1 0 2 mm year 1 is calculated for the period since the climatic optimum

new dates for first millennium bc tephra isochrones in ireland three distinct first millennium bc tephras bmr 190 omh 185 gb4 150 have been recognized in irish peat deposits including a previously undated ash bmr 190 we present the results of a programme of high precision 14c wiggle matching on a peat profile containing all three tephras from glen west county fermanagh northern ireland the wiggle match provides highly refined dates of 705 585cal bc for bmr 190 755 680cal bc for omh 185 and 800 758cal bc for gb4 150 the tephras constitute valuable widespread isochrones for palaeoecological research across the first millennium bc when a prolonged 14c calibration plateau between 750 and 400 cal bc presents a major problem to dating and correlating palaeoenvironmental events from multisite multiproxy studies of the period

composition and consequences of the intcal20 radiocarbon calibration curve radiocarbon calibration is necessary to correct for variations in atmospheric radiocarbon over time the intcal working group has developed an updated and extended radiocarbon calibration curve intcal20 for northern hemisphere terrestrial samples from 0 to 55 000 cal yr bp this paper summarizes the new datasets changes to existing datasets and the statistical method used for constructing the new curve examples of the effect of the new calibration curve compared to intcal13 for hypothetical radiocarbon ages are given for the recent holocene the effect is minimal but for older radiocarbon ages the shift in calibrated ages can be up to several hundred years with the potential for multiple calibrated age ranges in periods with higher resolution data in addition the intcal20 curve is used to recalibrate the radiocarbon ages for the glaciation of the puget lowland and to recalculate the advance rate the ice may have reached its maximum position a few hundred years earlier using the new calibration curve the calculated advance rate is virtually unchanged from the prior estimate

syn to post rift diapirism and minibasins of the central high atlas morocco the changing face of a mountain belt the atlas mountains are classically regarded as a failed mesozoic rift arm subject to alpine inversion folding and thrusting here we present new integrated structural and sedimentological studies that have revealed numerous early middle jurassic diapiric ridges and minibasins characterized by distinctive halokinetic structures diachroneity in halokinesis is observed across the central high atlas waning first in the sw during the early middle jurassic jbel azourki and tazoult ridges and continuing to late middle jurassic towards the ne imilchil region the halokinetic structures are readily differentiated from the effects of later alpine deformation allowing a new picture of the central high atlas to emerge the most pervasive deformation in the central high atlas is associated with early middle jurassic diapirism whereas the impact of alpine inversion is mostly focused at the basin margins this new understanding helps explain previously problematic aspects of the atlas mountains which we now recognize as an exceptionally well exposed natural laboratory for understanding the interactions between halokinesis tectonics and sedimentation

salt dome growth thrust fault growth and syndeformational stratigraphy la popa basin northern mexico abstract surface expression of two salt domes and a thrust fault in the la popa basin of northern mexico near monterrey nuevo leon suggest a complex history of interrelated salt tectonics late cretaceous clastic and carbonate sedimentation and thrust fault growth detailed stratigraphic analysis of clastic sediments and shallow marine carbonates of the difunta group campanian and maestrichtian near the two salt domes indicate that delta front sandstones thin and pinch out towards the salt domes successively higher sandstones lap higher and farther onto the domes and probably covered the domes completely during late cretaceous time though present day erosion precludes the certainty of complete coverage during high sea level stands algal and rudistid carbonate banks formed on the flanks of the domes and may also have covered the domes completely facies irregularities in the enclosing sedimentary rocks clearly indicate that the salt domes were active during late cretaceous time though hidden under the allochthonous block of the la popa fault a major northwest southeast trending thrust fault the presence of a third dome is implied by the occurrence of evaporites on the fault plane and by the presence of similar though smaller faults associated with the two exposed domes the la papa fault may be thought of as an out of the syncline southwest verging thrust fault with the overthrust block acting as a trap door for evaporites derived from the salt dome the largest carbonate bank in the basin the 250 meter 800 foot thick la popa limestone lentil occurs only on the upthrown side of this fault the downthrown side is comprised of an unusually thick approximately 4 600 meter 15 000 foot sequence of clastic rocks with an atypically high sand shale ratio this combination indicates that during high sea level stands carbonate banks grew on shoal areas that were present on the overthrust side of the fault during low sea level stands deltaic and shallow marine clastic sedimentation became concentrated in low areas associated with the down thrown side of the fault

a high precision age estimate of the holocene plinian eruption of mount mazama oregon usa the climactic eruption of mount mazama in oregon north america resulted in the deposition of the most widespread holocene tephra deposit in the conterminous united states and south western canada the tephra forms an isochronous marker horizon for palaeoenvironmental sedimentary and archaeological reconstructions despite the current lack of a precise age estimate for the source eruption previous radiocarbon age estimates for the eruption have varied and greenland ice core ages are in disagreement for the mazama tephra to be fully utilised in tephrochronology and palaeoenvironmental research a refined precise and accurate age for the eruption is required here we apply a meta analysis of all previously published radiocarbon age estimations n 81 and perform bayesian statistical modelling to this data set to provide a refined age of 7682 7584 cal yr bp 95 4 probability range although the depositional histories of the published ages vary this estimate is consistent with that estimated from the gisp2 ice core of 7627 150 yr bp zdanowicz et al 1999

high precision dendro 14c dating of two cedar wood sequences from first intermediate period and middle kingdom egypt and a small regional climate related 14c divergence abstract cedar cedrus sp wood from two archaeological contexts in egypt i the first intermediate period coffin of ipi ha ishutef ii a funerary boat at the pyramid of middle kingdom king senusret or sesostris or senwosret iii form floating tree ring sequences since one of the sample sets had been mounted with elmer s glue products in core mounts for dendrochronological examination we investigate whether pretreatment can remove this potential contaminant before 14c dating we find that even in unrealistic cases of extensive glue contamination this can be largely successfully removed making it likely that the samples in this study where moreover only wood samples without traces of glue were employed can provide accurate 14c dates dendro 14c wiggle matching was then employed to provide precise calendar dates for the two tree ring sequences the last extant ring of the ipi ha ishutef coffin lies ca 2081 2064 bc 95 4 probability supporting but refining its assumed date in the case of the senusret iii boat we find a temporary small but important offset within the period ca 2200 1900 bc in contemporary 14c ages between the levant and central and northern europe it is suggested this is likely a result of exaggeration of normal seasonal variations in the uptake of 14c and its latitudinal distribution caused by climate change in the 2200 1900 bc 4200 3900 cal bp y2k interval a date for the last extant ring of the senusret iii boat is probably around 1898 95 1879 76 bc 95 4 probability more consistent with a high middle kingdom egyptian chronology

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

the frequency of ice wedge cracking 1967 1987 at garry island western arctic coast canada the frequency of ice wedge cracking has been studied at garry island northwest territories for the 1967 1987 period sites have included low centre polygons intermediate centre polygons and polygons that do not fit any classification system analyses of crack frequency have included trough characteristics polygon characteristics and ice wedge types the results show that crack frequencies are highly variable within one site and also between two adjacent sites the correlation between crack frequency and a low air temperature is poor crack frequencies for a site with 59 wedges ranged from 8 to 42 between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75 between 1967 and 1987 in view of the wide range in crack frequencies at a given site the use of mean ice wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous the data show that the common twofold classification into active and inactive wedges is difficult to apply be

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

holocene sea level history of the canadian beaufort shelf new radiocarbon ages pertaining to the holocene sea level history of the canadian beaufort shelf are presented the ages were obtained on samples of freshwater and tidal marsh peat beds from offsho

late holocene climatic changes as detected by the growth and decay of ice wedges on the southern shore of hudson strait northern quebec canada the dating of cryoturbated palaeosols associated with past ice wedge activity on late holocene sandy fluvial terraces in a region of continuous permafrost leads to an interpretation of periods of ice wedge growth and active cracking that alternated with periods of decay dormancy and active layer deepening the reconstruc tion corresponds with palaeoclimatic information obtained from existing arctic wide and regional proxy rec ords the little ice age stands out as a period of intense ice wedge activity in the study area it was followed by a warm thawing interval during the first half of the twentieth century from ad 1946 to 1991 a well documented cooling of the climate took place which reactivated 94 of the studied ice wedges the pyramidal shape of ice wedge tops and the depths of the upgrowth features could be correlated between sites several kilometres apart clearly indicating a regional climatic response the mean annual air temperature dropped from about 7 8 c in 1946 to 8 9 c in 1991 the t