debris jets in continental phreatomagmatic volcanoes a field study of their subterranean deposits in the coombs hills vent complex antarctica abstract the ferrar large igneous province of antarctica contains significant mafic volcaniclastic deposits some of which are interpreted to fill large vent complexes such a complex was re examined at coombs hills to map individual steep sided cross cutting bodies in detail and we found several contrasting types two of which are interpreted to have filled subterranean passageways forcefully opened from below into existing non consolidated debris these transient conduits were opened because of the propagation of debris jets upward moving streams of volcaniclastic debris steam magmatic gases liquid water droplets following explosive magma aquifer interaction some debris jets probably remained wholly subterranean whereas others made it to the surface but the studied outcrops do not allow us to differentiate between these cases the pipes filled with country rock rich lapilli tuff or tuff breccia are interpreted to have formed following phreatomagmatic explosions occurring near the walls or floor of the vent complex causing fragmentation of both magma and abundant country rock material in contrast some of the cross cutting zones filled with basalt rich tuff breccia or lapilli tuff could have been generated following explosions taking place within pre existing basalt bearing debris well away from the complex walls or floor we infer that once focused jets were formed they did not incorporate significant amounts of existing debris while travelling through them instead incorporation of fragments from the granular host took place near explosion sites other basalt rich tuff breccia zones accompanied by domains of in situ peperite and coherent basalt pods are inferred to have originated by less violent processes

latest quaternary oceanographic changes in the okhotsk sea based on diatom records abstract the okhotsk sea is a locus of the north pacific intermediate water formation today the formation of the okhotsk intermediate water is linked with seasonal sea ice cover diatom records from the okhotsk sea show the following 1 during the last glacial maximum between 21 000 yr b p and 18 000 yr b p sea ice covered the western side of the sea throughout the whole year but the eastern part was open this permitted more efficient heat exchange with the atmosphere than waters and hence ventilation of the glacial okhotsk sea waters which in turn caused a greater extent of intermediate water formation through the bussol strait 2 the perennial sea ice cover extended northward and sea ice was present throughout the whole year over a great part of the sea except for the eastern part between 18 000 yr b p and 17 000 yr b p 3 the ice free area extended greatly to the south during the interval between 17 000 yr b p and 11 000 yr b p 4 there was no perennial ice cover over the whole sea and the ice free area that appeared as the seasonal ice area began to extend to the western part between 11 000 yr b p and 8 000 yr b p 5 after 8000 yr b p the ice free waters contracted to the present extent

mafic large volume pyroclastic density current deposits from phreatomagmatic eruptions in the ferrar large igneous province antarctica abstract mafic volcaniclastic deposits are increasingly recognized as important components of continental flood basalt provinces but the mode of origin of these deposits and the possible environmental influence of the eruptions that formed them remain poorly constrained the mawson formation ferrar large igneous province jurassic contains the best known examples of large scale mafic primary pyroclastic deposits from any flood basalt province worldwide at southern allan hills in contrast with other sites the mawson formation consists predominantly of subhorizontal laterally continuous meter thick layers that fall into four facies 1 poorly sorted coarse lapilli tuff or tuff breccia beds 2 tuff or fine lapilli tuff beds 3 block rich layers and 4 accretionary lapilli bearing beds we interpret the first facies as deposits of high concentration pyroclastic density currents pdcs resulting from the collapse of phreatomagmatic eruption plumes some from a source probably several kilomete

exceptional preservation processes of 3d dinosaur footprint casts in costalomo lower cretaceous cameros basin spain theropod dinosaur footprints at the costalomo tracksite pinilla de los moros formation upper hauterivian lower barremian western cameros basin salas de los infantes burgos province spain show unusual preservation of a previously undescribed nature the footprints occur as casts positive epireliefs at the top of a sandstone bed and preserve exceptional details of the top of the digit and claw morphology and of digital interactions with the sediment during penetration and extraction from the sediment footprint formation and preservation occurred in the following stages

reply to discussion of defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present by marchetti et al 2019

geomagnetic paleointensity dating of south china sea sediments for the last 130 kyr relative paleointensity records from the northern south china sea northwest pacific ocean were studied in two gravity piston cores continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples detailed rock magnetic parameters such as thermomagnetic and high field hysteresis data indicate that pseudo single domain magnetite in a narrow range of grain size and concentration is the main contributor to the remanent magnetization the uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records the relative paleointensity rpi curves were constructed by normalizing the natural remanent magnetization nrm with isothermal remanent magnetization irm both in the 20 60 mt demagnetization state dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores furthermore we have correlated our paleointensity records with napis 75 s atlantic 1089 sint 200 and nopapis 250 to determine the chronological rpi framework for the south china sea scs pis although some temporal offsets of paleointensity features between the different records have been recognized their similar shape suggests that relative paleointensity on the 10 3 10 4 year scale is globally coherent and can provide an age framework for sediments independent of delta 18 o ages c 2009 elsevier b v all rights reserved

phreatomagmatic eruptive and depositional processes during the 1949 eruption on la palma canary islands abstract in 1949 a 5 week long magmatic and phreatomagmatic eruption took place along the active volcanic ridge of la palma canary islands two vents duraznero and hoyo negro produced significant pyroclastic deposits the eruption began from duraznero vent which produced a series of deposits with an upward decrease in accidental fragments and increase in fluidal ash and spatter together inferred to indicate decreasing phreatomagmatic interaction hoyo negro erupted over a 2 week period producing a variety of pyroclastic density currents and ballistic blocks and bombs hoyo negro erupted within and modified an older crater having high walls on the northern to southeastern edges southwestern to western margins of the crater lay 50 to 100 m lower strongly contrasting deposits in the different sectors n se vs sw w were formed as a result of interaction between topography weak eruptive columns and stratified pyroclastic density currents tephra ring deposits are thicker and coarser grained than upper rim deposits formed along the higher edges of the crater and beyond the crater margin valley confined deposits are thicker than more thinly bedded mantling deposits on higher topography these differences indicate that the impact zone for the bulk of the collapsing tephra laden column lay within the crater and that the high crater walls inhibited escape of pyroclastic density currents to the north and east the impact zone lay outside the low sw w rims however thus allowing stratified pyroclastic density currents to move freely away from the crater in those directions depositing thin sections

response of western pacific marginal seas to glacial cycles paleoceanographic and sedimentological features abstract this paper reviews the recent progress in late quaternary studies in five northwestern pacific marginal seas especially the south china sea as an example a series of marginal seas separate asia from the pacific ocean and significantly modify the material and energy flux linkage between land and sea during glacial cycles the sea level induced environmental signal was amplified in the marginal seas giving rise to drastic changes in areas and configurations of these seas and to reorganization of sea water circulation in basins since most of the western pacific marginal seas are influenced by monsoon circulation and some of these are located within the western pacific warm pool the glacial geographic changes have produced a profound impact on regional and global climate for example the decrease of sea area and sea surface temperature sst in the marginal seas was one of the factors responsible for the enhanced aridity of inland china during the glaciation glacial intensification of the winter monsoon and increased seasonality of sst in marginal seas might explain at least partly the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open ocean records in this region as the western pacific marginal seas trap terrigenous material supplied by east asia the deep water sedimentation rates there can be one to two orders of magnitude higher than in the open ocean down slope sediment transport is more active when the sea level changes particularly during the deglaciation at least four types of carbonate cycles have been recognized in the western pacific marginal seas and each of those contains environmental signals from the surface and deep sea water as well as from the drainage basin

offshore transport of neritic diatoms as indicators of surface current and trade wind strength in the plio pleistocene eastern equatorial pacific abstract the taphonomy of neritic diatoms entrained into and transported offshore by the peru and south equatorial currents may represent fluctuations in surface current and southeast trade wind strength in the eastern equatorial pacific eep this proposition was investigated through the construction of a neritic pelagic diatom ratio npdr which is compared with other palaeoceanographic proxies analysed through the olduvai timeslab ca 2 0 1 75 ma at ocean drilling program sites 677 847 and 851 a new sea surface temperature sst record for all the sites is derived from a diatom transfer function and upwelling and bioproductivity records are provided by previously published radiolarian and caco3 data respectively for site 677 only results indicate a consistent relationship between proxy records suggesting that the presence of neritic diatoms in pelagic sediments are most likely attributable to surface current and trade wind variability the npdr has the potential of becoming an extremely useful micropalaeontological tool in multi proxy palaeoceanographic studies of coastal upwelling systems the palaeoceanographic history of the olduvai timeslab in the eep as indicated by previous studies is supported and enhanced by the npdr and new sst data reported here the early and late periods of the olduvai timeslab are characterised by strong upwelling low sst and high bioproductivity and increased trade wind strengths inferred from the npdr the mid olduvai 1 80 1 90 ma appears to have been a period of weaker upwelling higher ssts lower bioproductivity and decreased trade wind strength as indicated by the npdr the npdr is important as it increases our understanding of the relationship between palaeoceanographic processes and trade wind strength in the region

significance of the paralia sulcata fossil record in palaeoenvironmental reconstructions of the se asia marginal seas over the last glacial cycle

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

on the formation of eruption columns following explosive mixing of magma and surface water when magma vents into the sea or a crater lake the ensuing magma water interaction can affect the style of eruption dramatically if the mass of surface water incorporated into the erupting material is small 108 kg s the height progressively decreases with surface water content this occurs when the magma and surface water begin to constitute a significant fraction of the mass at the top of the column so that an increasing fraction of the initial magmatic thermal energy is converted to the surface water rather than the entrained air the transitions in eruption style which result from changes in the mass of surface water mixing with the magma may account for observations of both buoyant plumes and wet surge during the eruptions of taal in 1965 and miyake jima in 1983 and for the changes in the eruptive activity at surtsey in 1963 1964 as the access of seawater to the vent became more restricted we also present calculations which suggest that the accretionary lapilli which are often found in wet flow deposits may result from condensation of vapor in both the cold wet collapsing fountains and in the flows themselves

discussion defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present by lorenzo marchetti et al

holocene marine diatoms from the faeroe islands and their paleoceanographic implications abstract temporal oceanographic changes based on mid and late holocene marine diatom floras from the faeroe islands region have been studied the four studied coring sites are located in the skalafjord and a more open ocean environment the mouth of the kaldbaksfjord at water depths ranging between 50 and 70 m comparison of the diatom records in the fjord sediments with those from the outer part of the fjord shows that the fjord provides a more optimum potential for paleoceanographic reconstructions the concentrations of marine taxa and relative abundance of freshwater diatom species in the marine environment were analyzed with the aim of relating them to environmental conditions estimated diatom concentrations were very low and ranged from a maximum of 14 4 10 6 valves per gram dry sediment in the inner part of the fjord to a minimum of 0 1 10 6 outside the fjord the freshwater diatom flora that occurred between 1200 and 700 cal yr bp in the inner part of the fjord suggests much higher precipitation during this time and increased freshwater discharge into the fjord presence of actinocyclus normanii which is an indicator of increasing trophy is related to the first human settlement on the faeroe islands maximum likelihood factor analysis mlfa was used to describe the most essential relationship among the diatom species and to employ these relationships for inferring holocene environmental changes in the faeroe islands the first two mlfa factors are related to oceanic influences in the region factor 1 is represented by a warmer water diatom assemblage and is suggested to correspond to inflow of the norwegian atlantic current to the skalafjord whereas factor 2 is an indicator of a colder water diatom assemblage that corresponds to inflow of arctic norwegian water mixing anwm during the 4900 3200 cal yr bp time interval

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

diatoms in southeast pacific surface sediments reflect environmental properties abstract diatom abundance and assemblage composition determined for 47 surface sediment samples from the southeast pacific 50 s 15 n combined with existing data for the peru and chile margins demonstrate responses to regional temperature upwelling and productivity high diatom abundances valves g mark the eastern equatorial pacific upwelling and the coastal upwelling areas in particular the upwelling centers off peru freshwater diatoms reflect the low salinity tongue off the chilean fjords diatom species composition distinguishes between coastal and eastern equatorial pacific upwelling conditions and records sea surface temperatures q mode factor analysis defines five floral assemblages factors 1 and 4 determined by the genus chaetoceros f1 and thalassionema f4 reflect coastal and equatorial upwelling conditions respectively factors 2 and 3 characterized by the genus thalassiosira and azpetia nodulifera can be associated with el nino conditions a 5th factor described by paralia sulcata records a near shore upwelling center off point concepcion central chile statistical transfer functions relate diatom species percentages to sea surface temperature and productivity with error estimates of 0 9 c and 23 gc m 2 yr respectively and provide new tools for estimating past temperature and productivity along the west coast of south america

mafic volcaniclastic deposits in flood basalt provinces a review flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks mostly sills with any pyroclastic rocks limited to silicic compositions however mafic volcaniclastic deposits mvds exist in many provinces and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions the province where mvds are the most voluminous the siberian traps is also the one temporally associated with the greatest phanerozoic mass extinction a lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established but as a first step this contribution reviews in some detail the current knowledge on mvds for the provinces in which they are better known i e the north atlantic igneous province including greenland the faeroe islands the british isles and tephra layers in the north sea basin and vicinity the ontong java plateau the ferrar and the karoo we also provide a brief overview of what is known about mvds in other provinces such as the columbia river basalts the afro arabian province the deccan traps the siberian traps the emeishan and an archean example from australia the thickest accumulations of mvds occur in flood basalt provinces where they underlie the lava pile faeroes n1 km ferrar province z400 m siberian traps 700 m in the faeroes case the great thickness of mvds can be attributed to accumulation in a local sedimentary basin but in the ferrar and siberian provinces the deposits are widespread n310 5 km 2 for the latter on the ontong java plateau over 300 m of mvds occur in one drill hole without any overlying lavas where the volcaniclastic deposits are sandwiched between lavas their thickness is much less in most of the cases reviewed primary mvds are predominantly of phreatomagmatic origin as indicated by the clast assemblage generally consisting of basaltic clasts of variable vesicularity dominantly non to poorly vesicular mixed with abundant country rock debris the accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins east greenland ferrar karoo these underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity in the

diatom response to changes in palaeoenvironments of the northern south china sea during the last 15 000 years changes in palaeoenvironments over the last 15000 years have been documented by a high resolution diatom record of core 17940 from the northern slope of the south china sea four diatom assemblage zones each characterized by different diatom components are distinguished by cluster analysis t nitzschioides var parval t nitzschioides t nitzschioides var parva tnp tnp tn and the brackish littoral species used as the proxies for temperature and salinity are compared with previously published sea surface temperature fp 12e sstw and sea surface salinity sss data from the same core and with the dongge cave delta 18 o record the bolling allerod warm phase the younger dryas cold event the holocene climate optimum and three holocene cooling events 7150 6250 4150 3450 and 1800 1350 cal yr bp are clearly distinguished by changes in the abundance of the brackish littoral species and or in tnp tnp tn data a marked increase in the abundance of the coastal species paralia sulcata during the interval 11150 8050 cal yr bp indicates a strong coastal water influence probably due to both enhanced freshwater discharge from the pearl river and the opening of the taiwan strait this palaeoceanographic change might be caused partly by climate induced sea level lowering during the late pleistocene and the early holocene the palaeoceanography during most of the holocene appears to be primarily controlled by fluctuations in the east asian summer monsoon intensity c 2009 elsevier b v all rights reserved

preservation and erosion of theropod tracks in eolian deposits examples from the middle jurassic entrada sandstone utah u s a abstract the middle jurassic entrada sandstone exposed near the town of escalante southern utah consists of large scale cross bedded eolian deposits that are interbedded with horizontally laminated sand sheets and thin sets of eolian cross strata representing periods with a moister climate the flat bedded units contain numerous tracks and trackways from small to large sized theropod dinosaurs these tracks are today exposed in several distinct erosional states allowing detailed studies of track and undertrack formation in eolian deposits tracks that originally were emplaced on sloping surfaces show in their present day erosional state a morphology distinct from those originally emplaced on horizontal surfaces further the range of eroded track morphologies can help identify badly eroded tracks from nonbiogenic structures in similar deposits

characteristics and flux of settling particulate matter in neritic waters the southern yellow sea and the east china sea the typology and flux of settling particulate matter spm were investigated based on sediment trap sampling at six typical stations in the yellow sea and the east china sea the settling particulate matter in the neritic seas was sorted into three categories lithogenic particles living organisms and particle aggregates the mass of individual organisms is an important portion of particulate matter in the neritic waters the aggregates contain six types mucus aggregates fecal pellets diatom aggregates silicoflagellate aggregates tintinnids and miscellaneous aggregates of which the silicoflagellate aggregates and tintinnids are the most abundant in the yellow sea and the east china sea high particle fluxes such as 215 to 874 g m 2 day 1 spm in the bottom layer were found at three stations where the water was well mixed and the maximum flux was detected in the boundary area between the yellow sea and the east china sea where a wide nepheloid layer was present hence particle flux in neritic waters can be easily shifted by water turbulence the net vertical flux 123 to 961 mg c day 1 the contribution of lateral advection to resuspension flux 5 to 76 and the particulate organic carbon export ratio 18 to 60 were estimated for the other three stations where the water was stratified the highest values were all found in the upwelling area off the zhejiang coast suggesting that the area of high productivity provides a high net vertical flux of spm c 2010 elsevier ltd all rights reserved

珪藻paralia sulcataの増減からみた大陸系混合水の消長 東シナ海北東部の最終氷期 後氷期海洋環境

introduction to the river dominated shelf sediments of the east asian seas peter d clift1 jan harff2 3 jiaxue wu4 yan qiu5 department of geology and geophysics louisiana state university baton rouge la 70803 usa university of szczecin institute of marine and coastal sciences mickiewicza 18 pl 70 383 szczecin poland leibniz institute for baltic sea research seestrasse 15 d 18119 rostock warnemunde germany centre of coastal ocean science and technology sun yat sen university guangzhou 510275 china guangzhou marine geological survey china geological survey guangzhou 510760 china

paleoenvironmental studies of the korean peninsula inferred from diatom assemblages this paper presents a diatom history for korea and reviews some recent diatom analyses to reconstruct past environmental changes from terrestrial coastal and marine sediments around the korean peninsula since they were first reported by skvortzov in 1936 fossil diatom studies in korea have been conducted mainly from the neogene and quateranary strata of the pohang and gampo regions of gyeongsang bukdo and the chulwon and bukpyeong areas of gangwon do on the eastern coast of the korean peninsula as well as from holocene strata of the ilsan area of the han river estuary tidal sediments off mankyung dongjin namyang and hampyeong bay and the cheollipo area on the western coast of the korean peninsula most of the coastal diatoms provided further information on sea level trends climatic changes and coastal evolution for much of the holocene in the yellow sea recent studies of fossil diatoms from the ulleung basin east japan sea also indicate fluctuations in sea surface temperatures in the influx and circulation of the tsushima warm current and in sea levels during the late quaternary

short paper fossil vertebrate tracks and indenter mechanics a reconnaissance study is outlined showing how an improved understanding of the formation and character of fossil vertebrate tracks in soft sediments is provided by the application of the mechanical engineer s indenter theory supported by complementary scaled laboratory experiments only the footprint at the bottom of the shaft cut by the animal9s limbs in general offers the best preservation of the shape of the underside of the foot the character of the foot is less well preserved in the deformed bedding beneath the footprint and among laminae deposited in the shaft after the passage of the animal this understanding will help to reduce errors in the use of tracks in taxonomic biostratigraphic palaeoecological behavioural and environmental studies when a limbed vertebrate traverses yielding sediment the limbs deform the substrate into tracks which vary with the nature size and gait of the animal the forcefulness of its limb movements and the sediment properties most previous geological work on tracks and trackways has emphasized their taxonomic biostratigraphical palaeocological and behavioural significance lockley 1986 leonardi 1987 but without an adequate understanding of their environmental implications lockley 1986 and in particular their genesis and preservation as trace fossils the response of an elastic plastic material to an indenter or punch both in terms of theory calladine 1969 hill 1971 johnson et al 1982 and in the light of qualitative laboratory experiments provides a general mechanical model for track formation and a basis for the assessment of track preservation in sediments the indenter represents the animal9s

complex proximal deposition during the plinian eruptions of 1912 at novarupta alaska proximal 3 km deposits from episodes ii and iii of the 60 h long novarupta 1912 eruption exhibit a very complex stratigraphy the result of at least four transport regimes and diverse depositional mechanisms they contrast with the relatively simple stratigraphy and inferred emplacement mechanisms for the previously documented better known medial distal fall deposits and the valley of ten thousand smokes ignimbrite the proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta and numerous thin complex deposits of pyroclastic density currents pdcs with no regional analogs the locally dispersed component of the fall deposits forms sector confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100 300 m cf several kilometers for the medial distal fall deposits this locally dispersed fall material and many of the associated pdc deposits is rich in andesitic and banded pumices and richer in shallow derived wall rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition there are no marked contrasts in grain size in the near vent deposits however between locally and widely dispersed beds and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial distal samples associated pdc deposits form a spectrum of facies from fines poor avalanched beds through thin bedded landscape mantling beds to channelized lobes of pumice block rich ignimbrite the origins of the novarupta near vent deposits are considered within a spectrum of four transport regimes 1 sustained buoyant plume 2 fountaining with co current flow 3 fountaining with counter current flow and 4 direct lateral ejection the novarupta deposits suggest a model where buoyant stable regime 1 plumes characterized most of episodes ii and iii but were accompanied by transient and variable partitioning of clasts into the other three regimes only one short period of vent blockage and cessation of the plinian plume occurred separating episodes ii and iii which was followed by a single pdc interpreted as an overpressured blast involving direct lateral ejection in contrast regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume which were being strongly affected by short lived instabilities these instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent of the parameters that control explosive eruptive behavior only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

the importance of the transport system in shaping the growth and form of kimberlite volcanoes transport of kimberlite magma from the mantle to the surface is a complex process that involves many often sudden and dramatic changes in transport style the pace and magnitude of changes in the transport system acclerate as the magma nears the surface culminating in eruptions during which multiple transport events take place simultaneously as well as single transport events that change significantly from their point of origin to final deposition understanding the range of transport styles recorded by kimberlite deposits is key to describing the type and style of eruptions the growth of cones and craters and the distribution geometry and structure of the deposits that make up kimberlite volcanoes in an economic context building a clear picture of the processes that shape deposits is essential for selecting exploration targets and evaluating the grade and value of diamond bearing kimberlites variations in diamond grade reflect differences in the diamond content of different magma parcels erupted during the lifetime of the kimberlite volcano sorting during transport of eruption products or re working of diamonds during crater growth cone collapse and erosion deep transport systems control delivery of magma and diamonds to eruption sites the initial stages of kimberlite transport involve rise of magma in narrow interconnected networks of fluidfilled fractures there is compelling evidence that kimberlite magmas are extracted from their source region and erupted without significant residence times in the crust many single kimberlite volcanoes have significant variations in diamond grade between different kimberlite phases suggesting eruption of distinct perhaps unrelated magma parcels at the same site

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present abstract the morphology of fossil footprints is the basis of vertebrate footprint ichnology however the processes acting during and after trace fossil registration which are responsible for the final morphology have never been precisely defined resulting in a dearth of nomenclature therefore we discuss the concepts of ichnotaphonomy ichnostratinomy taphonomy biostratinomy registration and diagenesis and describe the processes acting on footprint morphology in order to evaluate the morphological quality of tetrapod footprints we introduce the concept of morphological preservation which is related to the morphological quality of footprints m preservation acronym mp and distinguish it from physical preservation p preservation acronym pp which characterizes whether or not a track is eliminated by taphonomic and diagenetic processes m preservation includes all the morphological features produced during and after track registration prior to its study and may be divided into substages ichnostratinomic registrational taphonomic stratinomic diagenetic moreover we propose an updated numerical preservation scale for m preservation it ranges from 0 0 worst preservation to 3 0 best preservation intermediate values may be used and specific features may be indicated by letters in vertebrate footprint ichnotaxonomy we regard the anatomy consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases only footprints showing a good morphological preservation grade 2 0 3 0 are useful in ichnotaxonomy whereas ichnotaxa based on poor morphological preservation grade 0 0 1 5 are considered ichnotaphotaxa nomina dubia characterized by extramorphologies we applied the preservation scale on examples from the palaeozoic to the present time including three ichnotaphotaxa and 18 anatomy consistent ichnotaxa morphotypes attributed to several vertebrate footprint producers results indicate the utility feasibility and suitability of this method for the entire vertebrate footprint record in any lithofacies strongly recommending its use in future ichnotaxonomic studies

coal fragment rank and contact relationships of debris avalanche and primary pyroclastic deposits in the mawson formation ferrar lip allan hills antarctica abstract mafic volcaniclastic deposits are known from many large igneous provinces and are generally ascribed to explosive phreatomagmatic activity that modifies the climatic effects of flood basalt volcanism the volcaniclastic deposits occur both as vent complex infills and as more widely dispersed deposits that may be strongly localized in pre lip topography at allan hills in the ferrar province of antarctica mafic volcaniclastic deposits are separated from country rock of the beacon supergroup by country rock derived sandstone breccias these are coarse monomict and matrix poor near the contact grade upward to polymict breccias derived from several country rock units and are overlain by mafic volcaniclastic deposits fragments of beacon coal show progressively higher rank away from the country rock contact interpreted to indicate heating by basaltic fragments in the volcaniclastic deposits the sequence overall is inferred to represent volcaniclastic deposits overlying a debris avalanche deposit with damaged in situ country rock at the base of the avalanche rocks in this area lie along one margin of volcaniclastic deposits extending over tens of kms 2 relationships among them are a reminder that analysis of contact zones is critical to establishing the origin and context of lip volcaniclastic deposits

three dimensional preservation of foot movements in triassic theropod dinosaurs dinosaur footprints have been used extensively as biostratigraphic markers environmental indicators measures of faunal diversity and evidence of group behaviour1 2 3 4 trackways have also been used to estimate locomotor posture gait and speed6 7 8 9 10 11 but most prints being shallow impressions of a foot s plantar surface provide little evidence of the details of limb excursion here we describe late triassic trackways from east greenland made by theropods walking on substrates of different consistency and sinking to variable depths that preserve three dimensional records of foot movement triassic theropod prints share many features with those of ground dwelling birds but also demonstrate significant functional differences in position of the hallux digit i foot posture and hindlimb excursion

siberian traps volcaniclastic rocks and the role of magma water interactions the siberian traps are one of the largest known continental flood basalt provinces and may be causally related to the end permian mass extinction in some areas a large fraction of the siberian traps volcanic sequence consists of mafic volcaniclastic rocks here we synthesize paleomagnetic petrographic and field data to assess the likely origins of these volcaniclastic rocks and their significance for the overall environmental impact of the eruptions we argue that magma water interactions including both lava water interactions and phreatomagmatic explosions in vents were important components of siberian traps magmatism phreatomagmatic episodes may have generated tall water rich eruption columns simultaneously promoting removal of highly soluble volcanic gases such as hcl and potentially delivering additional sulfur to the upper atmosphere