deglacial valley fill sedimentation pelly river yukon territory canada abstract a thick sequence of deglacial valley fill was studied along the pelly river yukon territory late wisconsinan deglaciation was by regional stagnation of the cordilleran ice sheet resulting in complex sequences of sediments deposited in glacial lakes many above stagnant ice more than 30 sections were described and measured and eight facies were recognized and interpreted the distribution of sediment reflects control by several systems 1 ice depositing basal tills 2 debris flows in glacial lakes depositing diamicton 3 meltwater streams depositing sorted sediment and 4 melting of underlying ice remobilizing and deforming previously deposited sediment a model is constructed that helps to explain sedimentation along pelly river material was deposited into lakes from melting ice valley slopes and adjacent valleys basal tills are relatively rare with most diamictons representing deposition by sediment gravity flows the presence of large thicknesses of highly disturbed sediments indicates that the sediments were deposited onto ice and subsequently failed undisturbed glaciolacustrine sediments were deposited either in more distal parts of the basin or after most of the ice had ablated the adjacent topography and the height of the glacial limits also influenced sedimentation steeper topography provided coarser sediments for deposition while low elevation of glacial limits reduced the availability of sediment even if steep slopes were present this study further contributes to models of supraglacial sedimentation by documenting that sedimentation was in several lake basins that lateral gradations in grain size are present and that fairly significant amounts of diamicton can be present

coarse grained sediment gravity flow facies in a large supraglacial lake near williams lake in the central interior of british columbia the fraser river exposes long sections of late pleistocene glaciolacustrine sediments selectively preserved within a bedrock trough the dominant facies types are thick normally graded gravels and sands that occupy steeply dipping multistorey channels up to 300 m wide and several tens of metres deep channels appear to have been simultaneously cut and filled by high density turbidity currents in a glacial lake floored by stagnant ice fining upward sediment gravity flow sequences up to 50 m thick may be the product of quasi continuous surging turbidity flows triggered by catastrophic meltwater discharges into the trough or retrogressive failure of ice cored sediments large scale post depositional deformation structures such as synclinal folds normal faults sedimentary dyke swarms and dewatering structures record gravitational foundering of sediment and pore water expulsion caused by the melt of underlying glacier ice melting of buried ice masses along the floor of the trough appears to have controlled the flow paths of turbidity currents by producing sub basins within the overlying sediment pile an idealized model of supraglacial lacustrine sedimentation is developed that may be applicable to other glaciated areas with similar bedrock topography

slope and deep shelf gully sandstones upper jurassic east greenland the upper jurassic hareelv formation of jameson land east greenland occurs in an area of 60 75 km it consists of 200 500 m of black shale with thick closely spaced sandstone bodies the sandstones fill deep steep walled gullies and elongate scours or form more regular laterally extensive parallel sided but erosive gully mouth or lobe deposits both types of sandstone bodies occur completely juxtaposed and systematic vertical or lateral trends in bed thickness or grain size have not been observed the sands were deposited in a deep water shelf basin by high density turbidity currents traveling from basin margin source areas a northeastern source area was represented by a short lived rapidly prograding delta whereas the main northwestern source area was a shallow sandy barrier occurring along the length of a major north northeast striking fault controlled slope voluminous turbidity currents probably were triggered by earthquakes in the fault zone the resulting slope and basinal sand bodies are up to 50 m thick and hundreds of meters wide and may be more than 5 km long in a downcurrent direction they occur in a thick rich oil prone source rock thus they may form potential stratigraphic reservoirs and help drain the source rock the hareelv formation shows important similarities to the ramp facies model for delta fed sand rich turbidite systems however the formation is mainly tectonically controlled and independent of eustatic sea level changes the hareelv formation may serve as a model for an unusual type of stratigraphic hydr carbon reservoir and at least one north sea oil field seems to have formed in an analogous setting

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

unifying criterion for the velocity reversal hypothesis in gravel bed rivers it has been hypothesized that velocity reversals provide a mechanism for maintaining pool riffle morphology in gravel bed rivers an important habitat for salmonids which are at risk in many places worldwide and that are the focus of extensive environmental legislation in europe and north america however the occurrence of velocity reversals has been controversial for over 3 decades we present a simple one dimensional criterion that unifies and explains previous disparate findings regarding the occurrence of velocity reversals results show that reversal depends critically on the ratio of riffle to pool width residual pool depth difference between pool and riffle elevations and on the depth of flow over the riffle suggesting that land management activities which alter channel form or divert water from the channel can have negative impacts on the sustainability of pool riffle habitat in gravel bed rivers

sedimentology and depositional model for glaciolacustrine deposits in an ice dammed tributary valley western tasmania australia quaternary sedimentary successions are described from the linda valley a small valley in western tasmania that was dammed by ice during early and middle pleistocene glaciations mapping and logging of exposures suggest that an orderly sequence of deposits formed during ice incursion occupation and withdrawal from tributary valleys four principal sediment assemblages record different stages of ice occupation in the valley as the glacier advanced a proglacial lacustrine sediment assemblage dominated by laminated silts and muds deposited from suspension accumulated in front of the glacier a subglacial sediment assemblage consisting of deformed lacustrine deposits and lodgement till records the overriding of lake bottom sediments as the glacier advanced up the valley into the proglacial lake as the glacier withdrew from the valley a supraglacial sediment assemblage of diamict gravel sand and silt facies formed on melting ice in the upper part of the valley a lacustrine regression in the supraglacial assemblage is inferred on the basis of a change from deposits mainly resulting from suspension in a subaqueous setting to relatively thin and laterally discontinuous laminated sediments occurrence of clastic dykes and increasing complexity of the geometry of deposits that indicate deposition in a subaerial setting a deltaic sediment assemblage deposited during the final stage of ice withdrawal from the valley consists of steeply dipping diamict and normally graded gravel facies formed on delta foresets by subaqueous sediment gravity flows the sediment source for the delta which prograded toward the retreating ice margin was the supraglacial sediment assemblage previously deposited in the upper part of the valley a depositional model developed from the study of the linda valley may be applicable to other alpine glaciated areas where glaciers flowed through or terminated in medium to high relief topography

an introduction to the rhynie chert the terrestrialization of life has profoundly affected the biosphere geosphere and atmosphere and the geological magazine has published key works charting the development of our understanding of this process integral to this understanding and featuring in one of the geological magazine publications is the devonian rhynie chert konservat lagerstatte located in aberdeenshire scotland here we provide a review of the work on this important early terrestrial deposit to date we begin by highlighting contributions of note in the geological magazine improving understanding of terrestrialization and palaeozoic terrestrial ecosystems we then introduce the rhynie chert the review highlights its geological setting the caledonian context of the rhynie basin and its nature at the time of deposition of the cherts which host its famous fossils there follows an introduction to the development of the half graben in which the cherts and host sediments were deposited the palaeoenvironment this represented and the taphonomy of the fossils themselves we subsequently provide an overview of the mineralization and geochemistry of the deposit and then the fossils found within the rhynie chert these include six plant genera which continue to provide significant insights into the evolution of life on land a range of different fungi with recent work starting to probe plant fungus interactions lichens amoebae and a range of unicellular eukaryotes and prokaryotes algae and cyanobacteria and finally a range of both aquatic and terrestrial arthropods through continued study coupled with methodological advances rhynie fossils will continue to provide unique insights into early life on land

geochronology of the tardree rhyolite complex northern ireland implications for zircon fission track studies the north atlantic igneous province and the age of the fish canyon sanidine standard abstract the british irish palaeogene igneous province bipip is part of the larger north atlantic igneous province and includes the lava fields of antrim mull and skye the tardree rhyolite complex trc in northern ireland forms an important stratigraphic unit between the lower and upper basalt formations of the antrim lava group alg previous zircon age determinations obtained from the trc have been used as a standard in zircon fission track studies but contradict several 40ar 39ar sanidine and u pb zircon results we provide new 40ar 39ar sanidine and u pb ca tims zircon ages which resolve this discrepancy two sanidine samples from the sandy braes vent and the columnar jointed dome forming rhyolites of tardree forest yield a weighted mean 40ar 39ar age of 61 13 0 42 ma 2 internal error ten u pb ca tims zircon analyses were undertaken eight of which employed the ca tims approach on both multi grain fractions and single grains six of the ca tims data yield a disequilibrium corrected weighted mean 206pb 238u age of 61 32 0 09 ma 2 the consistency of the 40ar 39ar ages with the ca tims u pb zircon age points to a closed system of both k and ar since eruption we propose that the crystallization age of the trc be taken as 61 32 0 09 ma and that the currently used age of the zircon fission track standard 58 4 0 7 ma be changed accordingly this also places the eruption of the trc in magnetochron c26r which is consistent with the reversed polarity magnetic remanence observed in the alg and supports the conclusion of ganerod et al 2010 that the lower basalt formation is older than the vaigat formation in western greenland no resolvable zircon inheritance has been detected by the tims analyses consistent with the fact that the temporal and geographic extent of rhyolitic magmatism within this sector of the bipip was very limited and hence was unlikely to provide inherited magmatic zircons from slightly older magmas antecrysts potentially older zircon xenocrysts would be derived from the underlying caledonian basement 400 ma or yet older rocks these should be easily detectable if the tardree zircon was to be employed as a u pb zircon standard the paired 40ar 39ar and 206pb 238u results from this study indicate an age of 28 393 0 194 ma for the widely used fish canyon sanidine standard and gives further support to the recent calibrations of kuiper et al 2008 and renne et al 2010

40ar 39ar dating of hydrothermal activity biota and gold mineralization in the rhynie hot spring system aberdeenshire scotland this study presents a new high precision 40ar 39ar age for the devonian hot spring system at rhynie hydrothermal k feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock date the hydrothermal activity the fossilised biota and syn k feldspar gold mineralization at 403 9 2 1 ma 2 oxygen isotope data for the parent fluid 4 to 2 show that the k feldspar was precipitated from a dominantly meteoric fluid which mixed with magmatic fluids from a degassing magma chamber the 40ar 39ar age 403 9 2 1 ma 2 when recalculated 407 1 2 2 ma 2 with respect to the astronomically tuned age for fish canyon sanidine 28 201 0 023 ma 1 also provides a robust marker for the polygonalis emsiensis spore assemblage biozone within the pragian earliest emsian furthermore the age identifies the devonian pull apart volcano sedimentary basins of the british and irish caledonides and their root zones as specific targets for future gold exploration

lateglacial ice dynamics of the cordilleran ice sheet in northern british columbia and southern yukon territory retreat pattern of the liard lobe reconstructed from the glacial landform record the liard lobe formed a part of the northeastern sector of the cordilleran ice sheet and drained ice from accumulation areas in the selwyn pelly cassiar and skeena mountains this study reconstru

sandy gravelly mass flow deposits in an ice marginal lake saalian leuvenumsche beek valley veluwe the netherlands with emphasis on plug flow deposits abstract in three pits in the leuvenumsche beek valley near ermelo and elspeet massive and diffusely banded clean gravelly sands found in association with sandy sediments showing some similarities to the bouma sequence were interpreted as originating from sediment gravity flows the flows which came to rest on a ca 6 paleoslope probably originated from slumping of parts of the ice pushed ridges at either side of an ice marginal lake major characteristic features in the three sand pits studied are u shaped channel forms with a maximum depth and width of 10 25 rmm the fills consist of sand and gravels locally containing giant sand clasts the sediments just below the base of these channel forms are commonly distorted and folded especially the massive more sandy fills are surrounded by a finer grained diffusely bedded and inversely graded zone these sedimentary features suggest that rigid sediment plugs sheared downslope generating a finer grained shear zone around the plug scouring a slide scar till its present semi cylindrical form and preserving the steep sides exceeding the angle of repose of the channel form by freezing the u shaped channel forms plugged troughs are locally overlain by shallower gently sided trough structures with mainly diffusely banded infillings very shallow and often smaller troughs are found again on top of these massive and diffusely banded infillings the sediments in these troughs consist of repetitions of two types of microsequences 1 thickly bedded sequences of normally graded massive sands near horizontal stratifications plane beds and cross bedded sets and 2 thinly bedded sequences of relatively thick units t a and thin units t c and t d of the bouma sequence the repetitions of the microsequences are interpreted as flow pulsations upwards thinning of the sequence together with a finer grain size may point to waning flow conditions their association with plugged troughs is suggestive of retrogressive flow slides

a depositional model for outwash sediment sources and hydrologic characteristics malaspina glacier alaska a modern analog of the southeastern margin of the laurentide ice sheet the malaspina glacier on the southern coast of alaska is a partial analog of the late wisconsinan laurentide ice sheet that occupied new england and adjacent areas ice lobes of the malaspina are similar in size to end moraine lobes in southern new england and long island estimated ablation rates surface slopes and meltwater discharge per unit of surface area for the laurentide ice sheet are comparable to measured ablation rates surface slopes and meltwater discharge rates for the malaspina glacier meltwater moves from the surface of the malaspina down glacier and toward the bed of the glacier along intercrystalline pathways and through a series of tunnels regolith beneath the glacier which is eroded and transported to the margin of the glacier by subglacial and englacial streams is the source of essentially all fluvial and lacustrine deposits on the malaspina foreland by analogy a similar hydrologic system existed at the southeastern margin of the laurentide ice sheet subglacial regolith which was eroded from beneath the ice sheet by meltwater was the source of most stratified sediment deposited in new england and adjacent areas during the late wisconsinan similarly wisconsinan ice contact landforms in new england were built by the same processes that are constructing landforms composed of stratified sediments in contact with the malaspina glacier for the malaspina glacier and the laurentide ice sheet therefore we reject the concept of the dirt machine by which debris near the base of the glacier is carried to the surface of the glacier along shear planes and then washed off the surface to form ice contact stratified deposits

a high precision u pb age constraint on the rhynie chert konservat lagerstatte time scale and other implications abstract an isotope dilution thermal ionization mass spectrometry u pb zircon age of 411 5 1 3 ma obtained from an andesitic lava occurring within the lower devonian rhynie outlier aberdeenshire ne scotland effectively dates the rhynie chert konservat lagerstatte biostratigraphical constraints on the rhynie chert bearing succession indicate that this age lies within the interval early but not earliest pragian earliest emsian accordingly the pragian emsian boundary must post date or closely approximate to 411 5 1 3 ma while the lochkovian pragian boundary must predate 411 5 1 3 ma integration of this new high precision age with an improved temporal framework for late caledonian intrusive activity in ne scotland suggests that the rhynie hot spring system the parental9 hydrothermal system to the rhynie cherts was unrelated to any newer granite9 intrusion rhynie was instead powered by a basaltic andesite magma whose generation and ascent were directly linked to the transcurrent fault movements responsible for the formation of the rhynie basin supplementary material details of analytical techniques id tims u pb geochronology and photomicrographs of zircon and titanite grains recovered from the milton of noth andesite are available at http www geolsoc org uk sup18463

stratigraphy optical dating chronology irsl and depositional model of pre lgm glacial deposits in the hope valley new zealand abstract a 110 m thick succession of glacial valley fill is described from poplars gully central south island new zealand the section consists of eight lithofacies assemblages that represent different stages of ice occupation in the valley basal sediments record an ice retreat phase followed by a glacial re advance which deposited mass flow diamictons and till a subsequent ice retreat from the site is indicated by the stratigraphic transition from till to thick glacio fluvial gravels this is followed by a probably short lived glacier re advance that caused folding and thrusting of proglacial sediments final glacial retreat from the valley led to the formation of a large proglacial lake in total poplars gully holds evidence for two major ice advances separated by a glacial retreat that resulted in complete ice evacuation from the lower hope valley infrared stimulated luminescence irsl dating on ice proximal sediments from poplars gully yielded six ages between 181 and 115 ka bp our stratigraphic logging and dating results show that the fill sequence was not as previously thought deposited in association with ice advances during the last glacial maximum lgm nor indeed during the last glacial cycle lgm glaciers later overran the fill but we find that the older glacial sequences are considerably more voluminous than those deposited during the last glacial cycle we also show that the mid pleistocene glaciers carved a much deeper valley trough than did glaciers during the lgm taken together these features are likely to reflect a significant difference in the magnitude of successive pleistocene glaciations in the valley with the mid pleistocene ice advances having been considerably larger than those of the last glacial cycle the recognition of the in situ survival of extensive pre mis 5 marine isotope stage deposits in valley troughs that were later occupied by lgm glaciers represents a new feature in the quaternary stratigraphy of the southern alps the results demonstrate that new zealand s commonly very large soft sedimentary valley fills provide a valuable yet largely unexploited terrestrial sedimentary archive of successive glaciations in the region

experimental hydrothermal alteration of partially metamict zircon we present the results of a series of hydrothermal experiments on grains from two partially metamict zircon samples from sri lanka in the temperature range 350 to 650 c and with different solutions 2 m alcl 3 2 m cacl 2 pure h 2 o and a multi cation solution under these conditions sharply bounded reaction fronts penetrated into the zircon grains and developed complex lobate and rim structures that resemble structures found in natural zircon systems the reaction zones are characterized by a marked increase in the cathodoluminescence intensity a decrease of the back scattered electron emission and an increased degree of structural order as revealed by micro raman and infrared spectroscopy sensitive high resolution ion microprobe and electron microprobe measurements revealed that the altered areas gained solvent cations e g ca 2 ba 2 mg 2 al 3 from the solution and lost variable amounts of zr si hf the ree u th as well as radiogenic pb a comparison between dry and hydrothermal annealing trends shows that the kinetics of structural recovery including recrystallization of the amorphous phase in metamict zircon is strongly enhanced under hydrothermal conditions this finding suggests that water catalyzes structural recovery processes in metamict zircon we found that the structure of the reacted areas does not resemble that of crystalline zircon i e is still characterized by a temperature dependent degree of disorder which would not be expected if the reaction is controlled by a coupled dissolution and re precipitation process instead the alteration process can be described best by a diffusion reaction recrystallization model in this model it is postulated that the diffusion of water into the metamict structure is the driving force for moving recrystallization fronts we found that the rate and the extent of solid state recrystallization of the amorphous phase is an important factor in determining the mobility of trace elements this interpretation is indicated by the observation that trace elements including u and th were preferentially lost during the reaction with a fluid at low temperatures where recrystallization of the amorphous material was slow or not activated at all the observed chemical alteration patterns are believed to reflect a competition between the kinetics of long range diffusion and ion exchange and the kinetics of the short range diffusion necessary for the recrystallization process

a devonian auriferous hot spring system rhynie scotland the early devonian rhynie hot spring system is the oldest known and is of the low sulphidation type it extends for at least 1 5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments plant bearing sinters and andesitic lavas the age of sedimentation and hydrothermal activity has been determined by palynological pragian and radio metric 396 12 ma techniques the outlier is a half graben with a complex stepped western margin the devonian rocks show intense hydrothermal alteration along the fault zone the main alteration minerals are quartz k feldspar calcite hematite and illitic and chloritic clays multiple chert veining and brecciation are widely developed and geyserite and vent material are also present pyrite occurs in veins and all alteration facies sinters and altered rocks contain high concentrations of au as sb hg w and mo gold occurs in arsenian pyrite and as sub micron particles in oxidized rocks the fluid s responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water however incursions of high temperature 300 440 c magmatic fluids occurred with d 65 and 18 o around 8 5 34 s pyrite and initial 87 sr 86 sr ratios vein calcite lie mainly within the ranges 3 4 to 8 5 and 0 71138 to 0 71402 respectively these data indicate that late proterozoic dalradian metasediments are a likely source for s and sr but other sources are possible 13 c values for caliche and vein calcite imply derivation of carbon from non organic sources the rhynie cherts were deposited from a low salinity fluid of probable meteoric origin 18 o chert 13 1 to 16 5 which had interacted with the basement rocks and sediments high xe ar br cl and i cl ratios plant bearing chert yielded an 40 ar 39 ar ratio 292 1 0 6 significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere

structural controls and origin of gold silver mineralization in the grampian terrane of scotland and ireland gold bearing mineral deposits occur over a strike distance of 300 km within the grampian terrane of scotland and ireland this terrane consists of neoproterozoic lower ordovician rocks of the dalradian supergroup that were polyphase deformed and metamorphosed during the c 470 ma grampian orogeny sulphide rich au ag deposits occur in scotland at calliachar urlar burn tombuie tyndrum and cononish and in ireland at curraghinalt omagh cavanacaw croagh patrick cregganbaun and bohaun they are hosted by 0 1 6 m thick quartz veins and have a similar overall mineralogy including native gold as cu fe pb and sn sulphides with hessite tetrahedrite and electrum present in the first six localities above the mineralized quartz veins which are characterized by open space textures crystallized at c 3 5 km depth in the crust all of the deposits were structurally controlled and apart from curraghinalt occur within second order riedel r r and t fractures resulting from a regional n s trending maximum principal stress these deposits are of upper silurian to lower devonian post scandian age and are inferred to have crystallized from hot silica rich metamorphic fluids derived from dehydration reactions at the greenschist amphibolite facies boundary curraghinalt is an older grampian thrust related deposit plutonic igneous rocks mainly granitoid contributed in part to the fluids which were channelled into major orogen parallel strike slip faults to be injected by fault valve pumping into the damage zones and fault breccias of newly formed riedel fractures any residual fluid probably percolated to the ground surface to form rhynie chert type hot springs

the influence of recent lead loss on the interpretation of disturbed upb systems in zircons from igneous rocks in east greenland abstract a series of caledonian igneous rocks from east greenland have been dated by means of u pb isotope determinations on zircons all discordias obtained give too low intercept ages in one case more than 200 ma younger than the rb sr mineral isochron age from the same sample leach experiments show that recent or subrecent loss of lead is responsible for the geologically meaningless ages obtained further it is shown that the recent lead loss is not caused by laboratory treatment but must be related to natural processes x ray investigations combined with transmission electron microscope analyses show a correlation between recent lead loss and the chemistry of the investigated zircons

sedimentation in a deep glacier fed lake lake tekapo new zealand surface sediments cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in lake tekapo sedimentation is dominated by the godley river which forms an extensive delta in the northern third of the lake delta growth accounts for 55 of annual sediment deposition in winter sandy muds are deposited at the top of the delta slope where they may move under gravity as a surficial slide oversteepening of the upper slope also generates deep seated failures the entire 20 km2 of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment down the delta slope sedimentation rates decrease surface sediments get finer and varves become better developed in the lake basin sediments are parallel bedded varves which contain typical winter summer annual cycles as well as minor non annual flood varves annual varve thickness and semi annual varve frequency are determined by variations in the discharge of the godley river sedimentation in the basin accounts for 40 of the budget and sedimentation rates decrease with distance from the delta except at the distal end of the basin where turbid underflows are stopped by the rising lake floor beyond the basin sedimentation rates decrease abruptly coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore the remaining 5 of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement which occasionally slumps to the basin floor

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

glacial sedimentary processes and environmental reconstruction based on lithofacies glacigenic sediments exposed in pits around villeneuve near edmonton alberta are subdivided into facies based on grain size sedimentary structure glacially induced deformation and faulting and groove marks two diamicton facies are recognised one of which is interpreted as a primary till deposited directly from glacier ice and the other as a product of mass movement the diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits the stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities at any one place the glacier appears to have alternated between being attached to the bed causing thrusting and sole marking and being separated from the bed by a cavity in which fluvial and mass movement sediments accumulated the net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance the correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history in addition the interpretations presented here have implications regarding the formation of soft zones in till they indicate that the soft zones are beds of sorted sediment redeposited by mass movement

discussion on a high precision u pb age constraint on the rhynie chert konservat lagerstatte time scale and other implications journal vol 168 863 872 we welcome the contribution of parry et al 2011 concerning the age of the globally important rhynie hot spring system aberdeenshire scotland however although we accept that they have provided a valuable and robust u pb age constraint for the milton of noth andesite and the rhynie outlier stratigraphic succession we do not accept that they have constrained the timing of hot spring activity as suggested the geophysical trace of the unexposed milton of noth andesite indicates that it lies immediately adjacent to the rhynie fault zone and runs parallel to it for some 2 km it may even lie within the rhynie fault zone see discussion by rice ashcroft 2004 its stratigraphic position is therefore uncertain parry et al 2011 stated that the exact stratigraphic position is not important because their preferred stratigraphic locations lie within the tillybrachty sandstone and dryden flags formations both of which have consistently yielded spores belonging to the polygonalis emsiensis spore assemblage biozone this assertion is not valid the polygonalis emsiensis spore assemblage biozone may have lasted several million years and thus potentially there could be a significant hiatus between eruption of the andesite and the onset of hot spring activity they further assume that the andesite was linked to an andesitic magma chamber at depth which powered the hydrothermal system this remains speculation accepting the uncertainty in the stratigraphic position and by asserting a maximum thickness of sediment between the andesite and the rhynie cherts and a conservative deposition rate parry et al 2011 attempted to temporally link the andesite to the cherts by calculating the time interval represented by the intervening sediment the estimation of time depends on the absence of unconformities disconformities and faulting with such assumptions and uncertainties casting doubt on the thickness of the intervening sediments

subaqueous outwash deposits in the ingraham ridge chazy new york a 1 5 km segment of ingraham ridge a stratified sand and gravel ridge in northeastern new york is composed dominantly of subaqueous outwash deposits the core of the ridge segment may include subordinate subglacial tunnel deposits the subaqueous outwash is composed mainly of interbedded sediment gravity flow bar dune and ripple deposits that occur in channels sheetlike cross stratified and cross laminated deposits also are common particularly on the distal western margin of the ridge segment the ridge segment is draped by glaciolacustrine laminated sand silt and clay and glaciomarine massive mud westward decrease in grain size and scale of sedimentary structures is attributed to confining ice walls of an asymmetric embayment sediments are deformed in part by the melting of adjacent and buried ice the ridge was modified during champlain sea regression and the reworked deposits were colonized by shallow water organisms reworking may have been minor and the broad low morphology of the ridge

late pleistocene stratigraphy and chronology of lower chehalis river valley southwestern british columbia evidence for a restricted coquitlam stade sediments in lower chehalis valley span middle wisconsin olympia nonglacial interval to holocene time sediments are divided into six units with chronological control provided by 14 new radiocarbon ages fluvial gravel spans the transition from the late olympia nonglacial interval to the early fraser glaciation glaciolacustrine sedimentation represents the first definitive glacial activity in the valley and indicates that vashon ice in the fraser lowland blocked the mouth of the chehalis valley at ca 18 17 ka bp ice then flowed down the chehalis valley the chehalis valley deglaciated while ice persisted in the fraser lowland forming another lake after this lake drained terraces and fans formed this style of glaciation deglaciation is typical of many watersheds peripheral to the fraser lowland in that local valley ice was slightly out of phase with ice in the lowland this resulted in glacial lakes forming during both advance and retreat phases however in contrast to watersheds in the northwestern fraser lowland no definitive evidence of a coquitlam ice advance was found within the chehalis valley although glaciers in the area were likely active and advancing data from the chehalis valley indicates that they were not as extensive as previously thought since ice source areas in the northeastern fraser lowland are in the leeward area of the coast mountains it is suggested that lower precipitation resulted in limited glacier activity there during the coquitlam stade

coarse grained sediment flow facies in a large supraglacial lake discussion sur l article de eyles n clark b m and clague j j 1987 sedimentology vol 34 93 216