changes in terrestrial floras at the triassic jurassic boundary in europe abstract one of the biggest mass extinctions took place at the triassic jurassic boundary it affected both marine and terrestrial ecosystems and caused the disappearance of many animal taxa mostly marine ones its influence on floral changes has been widely discussed with arguments offered for the sudden mass extinction of plants over vast areas or alternatively for slow less extensive changes the aim of this study was to statistically verify changes in terrestrial plant composition during the tjb in europe and to examine the type and extent of these changes data from polish localities an interesting new addition to the floristic data from the tjb were compared with those from other selected localities in europe the database contains 311 macroflora taxa from 106 localities 16 polish in 13 countries grouped into 29 regions and 571 microflora taxa from 105 localities 29 polish in 11 countries grouped into 37 regions the analysed data cover the period from the anisian to the toarcian stages range based metrics for diversity dynamics were calculated to show trends in floral changes during the studied time interval the focus being on the tjb due to strong disproportions in the number of localities and occurrences the rhaetian and the hettangian stages were overrepresented the warm and humid climate of those stages promoted plant diversity and led to the formation of numerous broad floodplains conducive to the preservation of remains e g in coal the patterns established by the raw data analyses were also assessed by applying a sampling standardisation procedure our results based on accurate data from poland and the rest of europe confirm and visualize a scenario in which there were no significant changes in terrestrial plant composition at the tjb hierarchical clustering suggests that local habitat conditions are the key factor in the grouping of localities with similar floristic composition and that differences between floras are not associated with the time dimension stages

equatorial spread f instability conditions as determined from ionograms conditions of plasma irregularity or spread f generation under the rayleigh taylor mechanism in the nighttime equatorial ionosphere are examined from ionogram data registered over fortaleza 4 s 38 w mag dip lat 1 7 brazil for a one year period the results show that local ionospheric conditions such as the bottomside f region electron density scale length and the ion neutral collision frequency at the base of the layer at sunset hours determine the generation of the spread f irregularities over the equator in the post sunset hours

an analysis of the quiet time day to day variability in the formation of postsunset equatorial plasma bubbles in the southeast asian region presented is an analysis of the occurrence of postsunset equatorial plasma bubbles epbs detected using a global positioning system gps receiver at vanimo the three year data set shows that the epb occurrence maximizes minimizes during the equinoxes solstices in good agreement with previous findings the vanimo ionosonde station is used with the gps receiver in an analysis of the day to day epb occurrence variability during the 2000 equinox period a superposed epoch analysis sea reveals that the altitude and the change in altitude of the f layer height is 1 standard deviation 1 larger on the days for which epbs were detected compared to non epb days these results are then compared to results from the thermosphere ionosphere electrodynamics general circulation model tiegcm which show strong similarities with the observations the tiegcm is used to calculate the flux tube integrated rayleigh taylor r t instability linear growth rate a sea reveals that the modeled r t growth rate is 1 higher on average for epb days compared to non epb days and that the upward plasma drift is the most dominant contributor it is further demonstrated that the tiegcm s success in describing the observed daily epb variability during the scintillation season resides in the variations caused by geomagnetic activity as parameterized by kp rather than solar euv flux as parameterized by f10 7 geomagnetic activity varies the modeled high latitude plasma convection and the associated joule heating that affects the low latitude f region dynamo and consequently the equatorial upward plasma drift key points day to day epb occurrence in southeast asia investigated using ground based gps tiegcm exhibits similiar daily variability to the epb observations small changes in kp strongly influence daily epb occurrence variability

on post midnight field aligned irregularities observed with a 30 8 mhz radar at a low latitude comparison withf layer altitude near the geomagnetic equator 1 we investigated the relationship between post midnightf region field aligned irregularities fais andf layer altitude by analyzing data of a 30 8 mhz radar installed 5at kototabang indonesia 0 2 s 100 3 e geomagnetic latitude 10 4 s and an ionosonde installed at chumphon thailand 10 7 n 99 4 e geomagnetic latitude 3 3 n chumphon is located near the geomagnetic equator on approximately the same meridian as kototabang case studies show that the altitude of thef layer rose at chumphon a half hour before the post midnight fais appeared at kototabang the doppler velocity of thee region fais observed simultaneously by the 30 8 mhz radar was downward indicating that thef layer uplift was not caused by the electric field we also investigated seasonal variations of the post midnight fai occurrence and thef layer altitude both the post midnight fais and the uplift of thef layer were frequently seen around midnight between may and august the seasonal variation of the midnightf layer uplift around the geomagnetic equator coincided with that of the post midnight fai occurrence at kototabang these results suggest that the uplift of thef layer would play an important role in the generation of post midnight fais we evaluated the linear growth rate of the rayleigh taylor instability based on the altitude of thef layer observed at chumphon the result shows that the uplift of thef layer can enhance the growth rate because gravity driven eastward electric current increases therefore we interpret that the observed fais were accompanied by plasma bubble the growth rate of which was reinforced by the upliftedf layer

determination of 88sr 86sr mass dependent isotopic fractionation and radiogenic isotope variation of 87sr 86sr in the neoproterozoic doushantuo formation abstract we measured both mass dependent isotope fractionation of 88sr 88sr 86sr and radiogenic isotopic variation of sr 87sr 86sr for the neoproterozoic doushantuo formation that deposited as a cap carbonate immediately above the marinoan related nantuo tillite the 88sr and 87sr 86sr compositions showed three remarkable characteristics 1 high radiogenic 87sr 86sr values and gradual decrease in the 87sr 86sr ratios 2 anomalously low 88sr values at the lower part cap carbonate and 3 a clear correlation between 87sr 86sr and 88sr values these isotopic signatures can be explained by assuming an extreme greenhouse condition after the marinoan glaciation surface seawater mixed with a large amount of freshwater from continental crusts with high 87sr 86sr and lighter 88sr ratios was formed during the extreme global warming after the glacial event high atmospheric co2 content caused sudden precipitation of cap carbonate from the surface seawater with high 87sr 86sr and lighter 88sr ratios subsequently the mixing of the underlying seawater with unradiogenic sr isotope compositions and normal 88sr ratios probably caused gradual decrease of the 87sr 86sr ratios of the seawater and deposition of carbonate with normal 88sr ratios the combination of 87sr 86sr and 88sr isotope systematics gives us new insights on the surface evolution after the snowball earth

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

87sr 86sr chemostratigraphy of neoproterozoic dalradian carbonates below the port askaig glaciogenic formation scotland abstract the neoproterozoic cambrian dalradian supergroup of scotland contains three glaciogenic sedimentary units the port askaig formation the stralinchy reelan formation and the loch na cille boulder bed in ascending order although the idea that relatively cold climates occurred during the latest proterozoic is widely accepted the cause of the onset of glaciation is still controversial we use new carbonate 87 sr 86 sr data to better constrain this environmental change some dalradian limestones have high strontium contents 1000 ppm low manganese contents and mn sr ratios 87 sr 86 sr values of paleoseawater in the neoproterozoic the 87 sr 86 sr values of limestones of the islay formation ca 0 7067 sampled on the island of islay are similar to the values of previous studies however the 87 sr 86 sr values of limestones just below the port askaig formation ca 0 7064 collected on the island of garbh eileach have the lowest values recorded in the dalradian supergroup comparing these 87 sr 86 sr values with coeval 87 sr 86 sr values of other regions in the world such low 87 sr 86 sr i87 sr 86 sr ratio from the tonian through the cryogenian and ediacaran to the earliest cambrian the results show that the 87 sr 86 sr ratio of seawater decreased just before the older cryogenian glaciation that it increased by two steps in the early and middle ediacaran and that there were at least two abrupt positive excursions in the middle ediacaran and at the precambrian cambrian boundary the decline of the 87 sr 86 sr ratio of seawater just before the older cryogenian sturtian glaciation suggests that enhancement of weathering related to break up of the rodinia supercontinent and continental flood basalt volcanism was a likely driver for generating global cooling for the snowball earth conditions godderis et al 2003 donnadieu et al 2004

pennsylvanian fossil forests in growth position t0 assemblages origin taphonomic bias and palaeoecological insights abstract fossil forests buried in growth position in a geological instant t 0 assemblages are far more abundant in pennsylvanian successions than in any other part of the geological record in this review paper we evaluate the fundamental controls on the origin of these phenomena investigate the taphonomic biases that influence their composition and summarize their palaeoecological significance following earlier workers we highlight that high rates of burial and accommodation are essential for the formation and preservation of t 0 assemblages contexts especially favourable for their origin include ashfalls proximal to volcanic centres coastal plains drowned by relative sea level rise and fluvial environments such as channel bars crevasse splays and distributary lobes long term preservation requires high rates of subsidence consequently the vast majority of palaeozoic t 0 assemblages are confined to wetland settings at or close to sea level whereas drylands are poorly represented and uplands rarely sampled if ever however this is not the only major bias in the fossil record taphonomic processes selectively preserve plants dependent on their anatomy and stature and on groundwater chemistry thus although t 0 assemblages offer unrivalled insights into the nature of ancient forests whole plant reconstructions tree density canopy height productivity plant hydraulics cohort dynamics spatial heterogeneity ecological gradients tree sediment interactions and animal plant interactions to name but a few it is naive to believe they provide photographic snapshots9 of palaeoecosystems none the less careful taphonomic analysis of t 0 assemblages offers the potential for a nuanced understanding of these evocative phenomena and much remains to be learned from these important palaeoecological resources

community heterogeneity of early pennsylvanian peat mires reconstructions of pennsylvanian coal swamps are some of the most common images of late paleozoic terrestrial ecosystems all reconstructions to date are based on data from either time averaged permineralized peats or single site collections an erect in situ early pennsylvanian forest preserved above the blue creek coal black warrior basin alabama was sampled in 17 localities over an area of 0 5 km 2 resulting in the first temporally and spatially constrained pennsylvanian mire data set this three tiered forest was heterogeneous lycopsid and calamitean trees composed the canopy and lepidodendrids lepidophloios and sigillarians grew together at most sites more juvenile than mature lycopsid biomass occurs in the forest floor litter indicating a mixed age multicohort canopy pteridophytes tree fern and pteridosperms seed fern dominated as understory shrubs whereas sphenophyllaleans pteridophytes and pteridosperms composed the ground cover and liana tier the proportion of canopy understory and ground cover biomass varied across the forest low proportions of ground cover and liana taxa existed where canopy fossils accounted for 60 of the litter there is a distinct spatial clustering of sites with more or less understory or ground cover where canopy contribution was 60 where canopy biomass was low 50 understory shrubs contributed more biomass indicative of light interception and or competition strategies sphenopteris pottsvillea a ubiquitous ground cover plant is abundant in all sites except one where pteridosperm creepers and lianas dominate the litter interpreted to indicate total suppression of other ground cover growth ecological wet dry gradients identified in other pennsylvanian swamps do not exist in the blue creek mire with the interpreted wettest lepidophloios driest sigillaria and intermediate lepidodendron sensu latu taxa coexisting in most assemblages

forest dynamics and tip up pools drive pulses of high carbon accumulation rates in a tropical peat dome in borneo southeast asia singapore national research foundation singapore mit alliance for research and technology

on seeding large scale wave structure equatorial spread f and scintillations over vietnam 1 understanding the day to day variability in occurrence of equatorial spread f esf remains as a high priority objective in space weather research a major difficulty has been an inability to resolve the roles being played by large scale wave structure lsws and the post sunset rise pssr of the equatorial f layer in the production of esf in this paper we show conclusively that total electron content tec measured as a function of latitude and longitude provides clear routine descriptions of lsws then together with ionosonde data we show for the first time that while a seed for lsws can occur in the late afternoon its amplification takes place mostly during the pssr implications of these findings are discussed in light of existing theories

short paper the depositional age of the dalradian supergroup u pb and sm nd isotopic studies of the tayvallich volcanics scotland zircons from a keratophyre associated with the tayvallich volcanics in the dalradian rocks of the sw scottish highlands have been dated by u pb methods yielding an age of 595 4 ma this age indicates that most or all of the dalradian is precambrian in age and that dalradian sedimentation may have lasted for about 200 million years the age also constrains the time interval between cessation of dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the grampian orogeny sm nd isotopic data for the tayvallich volcanins and related metadolerite sills yield initial ond values of 2 to 4 which are thought to reffect the effects of melting of lithospheric mantle

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

peat accumulating depositional systems of sarawak east malaysia many coal deposits originate in deltaic estuarine and coastal plain settings and a knowledge of interrelationships between the tectonic and depositional elements active at the time of sediment deposition is necessary to formulate basin scale models the prograding coastal depositional systems of sarawak all contain domed peat accumulating environments in which low ash low sulfur peats are being deposited in areas of active clastic siliciclastic sedimentation these depositional systems are as large as 11 400 km2 and individual peat deposits within systems are in excess of 20 m thick and 1000 km2 in area the geographic positions and drainage basin areas of each depositional system are controlled by fault and fold systems although prograding into the same receiving basin individual system geomorphology is variable and ranges from a wave dominated microtidal delta to a wave dominated meso to macro tidal delta coastal plain system to a tide dominated macrotidal estuarine embayment along a 450 km stretch of coastline system variation is a function of sediment supply shelf and embayment geometry wave climate and tidal range these factors which control depositional system geomorphology also control the resulting long axis orientation of the thick domed peat deposits the surface vegetation and internal characteristics of most domed peat deposits however are similar internal characteristics consist of basal high ash high sulfur degraded peats overlain by low ash low sulfur well preserved peats in vertical profile these systems demonstrate variable responses to late pleistocene holocene sea level rise and in these instances the variation is most attributable to local differences in siliciclastic sediment supply which is a function of the drainage basin area

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

provenance and sediment dispersal in the rajang river delta coastal plain system sarawak east malaysia preliminary sedimentologic investigations were conducted in the rajang river delta coastal plain system in sarawak east malaysia to determine the processes and timing of siliciclastic transport and sedimentation in tropical peat dominated systems methods involved depth profiling and collection and analysis of bottom and suspended sediment load samples from channels and offshore areas and coring and trenching of subaerial channel shoreline and backswamp features the rajang delta occurs in an embayment formed by the folded mesozoic and cenozoic sediments of the central borneo massif it covers an area of 11 000 km2 and is physiographically separated into an alluvial valley floodplain an abandoned tidally flushed delta plain and an actively accreting rectilinear delta coastal plain from 50 to 80 of the surface area is covered by peat 1 to 20 m thick during the dry season of july august 1992 river channels varying from 2 to 45 m deep with discharge rates from 100 to approximately 3550 m3 s were carrying suspended sediment loads ranging from 0 to 2281 mg l at present approximately 8 2 x 10 10 kg yr of fine grained sediment is supplied to the system and areal accretion rates are over 1 0 km2 yr the structural configuration of the uplands receiving basin and subsequent drainage patterns and tidal influence results in a contradictory distribution of mature fine grained sediments in the channels of the active delta coastal plain and immature coarse grained angular sands and gravels in the channels of the abandoned delta lobe the contemporaneity of the peat and clastic accumulation is evidenced by the margins of the thick domed low ash peat deposits interfingering with and being overlain by root penetrated siliciclastic sediments much of the fine grained sediment however bypasses the delta plain due to in channel density gradients delta coastal plain accretion occurs by distributary mouth bar buildup sand bar welding and ridge and runnel accretion all subaerially exposed surfaces are quickly vegetated the aberrant depth and configuration of some channels suggest that drainage is in part controlled by contemporaneous faulting

explicit characteristics of evolutionary type plasma bubbles observed from equatorial atmosphere radar during the low to moderate solar activity years 2010 2012 using the fan sector backscatter maps of 47 mhz equatorial atmosphere radar ear at kototabang 0 2 s geographic latitude 100 3 e geographic longitude and 10 4 s geomagnetic latitude indonesia the spatial and temporal evolution of equatorial plasma bubbles epbs were examined to classify the evolutionary type epbs from those which formed elsewhere and drifted into the field of view of radar a total of 535 epbs were observed during the low to moderate solar activity years 2010 2012 out of which about 210 39 are of evolving type and the remaining 325 61 are drifting in epbs in general both the evolving type and drifting in epbs exhibit predominance during the postsunset hours of equinoxes and december solstices interestingly a large number of epbs were found to develop even a few minutes prior to the apex sunset during equinoxes further the occurrence of evolving type epbs exhibits a clear secondary peak around midnight 2300 0100 lt primarily due to higher rate of occurrence during the postmidnight hours of june solstices a significant number 33 of postmidnight epbs generated during june solstices did not exhibited any clear zonal drift while about 14 of epbs drifted westward also the westward drifting epbs are confined only to june solstices the responsible mechanisms for the genesis of fresh epbs during postmidnight hours were discussed in light of equatorward meridional winds in the presence of weak westward electric fields

lower devonian coaly shales of northern new brunswick canada plant accumulations in the early stages of terrestrial colonization abstract we describe two early devonian occurrences of coaly shale composed mainly of the compacted remains of early plants such that they resemble coal among the earliest thick phytodebris accumulations known the occurrences lie within pragian strata of the val d amour formation and emsian strata of the campbellton formation of northern new brunswick and were deposited in low energy wetlands where they were rapidly buried although the coaly shales did not yield recognizable plant taxa numerous taxa are present in adjacent beds petrographic analysis revealed an average of 80 7 vitrinite predominantly telovitrinite and 18 7 liptinite predominantly sporinite on a mineral matter free basis with a higher vitrinite content than most devonian coals low sulfur content and atomic c n ratios that vary from 44 3 to 82 1 in organic rich samples indicate terrestrial derivation vitrinite reflectance in organic rich samples 21 4 35 6 wt total organic carbon ranges from 0 48 to 1 00 indicating a low degree of thermal alteration that is supported by cross polarization spectra from studies of 13c nuclear magnetic resonance two carbon poor samples were thermally altered to anthracitic rank adjacent to an intrusive body although plants at this time were still comparatively primitive the presence at both sites of specimens with recognizable lignified cellular structures in vitrinite and particularly thick and resistant cuticle may represent an important step in peat development in these early devonian formations diverse assemblages of small vascular plants are present in a range of environments and the plants were sufficiently abundant to form coal like accumulations under suitable burial conditions serving as a proxy for plant biomass and vegetation cover in the early stages of terrestrial colonization

lignin land plants and fungi biological evolution affecting phanerozoic oxygen balance as dominance shifted from lycopsids and pteridophytes in the paleozoic to gymnosperms in the mesozoic to angiosperms in the tertiary plant architecture became more sparing in its use of lignin lignin degrading organisms were rare or absent in the paleozoic but diverse and abundant in the tertiary thus the terrigenous organic carbon cycle has quickened over time the fraction of terrestrial primary production preserved in coals and kerogens has declined and terrestrial production has been able to increase over time without concomitant rises in atmospheric o sub 2

dalradian slides and basin development a radical interpretation of stratigraphy and structure in the sw and central highlands of scotland movements on syndepositional listric faults are responsible for many of the lateral variations in dalradian stratigraphy sedimentary facies and thickness variations show that the surface traces of these faults correspond in many cases to what have previously been interpreted as tectonic slides although normal faults thrusts and sedimentary contacts may also mark their position three main episodes of faulting are described in the islay to lochaber area appin group sedimentation was controlled by a fault now represented by the loch skerrols thrust fort william slide ossian steep belt in the islay jura area an anomalously thick islay subgroup succession accumulated in a half graben bounded by a listric normal fault to the nw and terminated by transfer faults at each end the deposition of a thick easdale subgroup section was controlled by movements on what is now the benderloch ballachulish slide this listric fault terminates southwards in the scarba fault and probably extends north into the ossian steep belt the thinness of the appin and lower argyll group succession between the ericht laidon and bridge of balgie faults is an original feature the stratigraphic gap represented by the boundary slide here is reinterpreted as a disconformity however further east the boundary slide may well be a listric fault movement on which accommodated the thick succession around schiehallion the development of the major structure was influenced by the geometry of the sedimentary basins the schiehallion tummel area is reinterpreted as lying on the lower limb of the ben lui fold this resolves the problem of the emplacement of the tay nappe which is likely to be a gravity structure derived from above the ossian steep belt

87sr 86sr chemostratigraphy of neoproterozoic dalradian limestones of scotland and ireland constraints on depositional ages and time scales new calcite 87 sr 86 sr data for 47 limestones from the metamorphosed and deformed neoproterozoic cambrian dalradian supergroup of scotland and ireland are used to identify secular trends in seawater 87 sr 86 sr through the dalradian succession and to constrain its depositional age dalradian limestones commonly have sr 1000 ppm indicating primary aragonite and marine diagenesis low mn mn sr 18 o and trace element data indicate that many 87 sr 86 sr ratios are unaltered since diagenesis despite greenschist to amphibolite facies metamorphism consistent with the documented behaviour of sr and o during metamorphic fluid rock interaction thus the 87 sr 86 sr data are interpreted largely to reflect 87 sr 86 sr of coeval seawater currently available data show that neoproterozoic seawater 87 sr 86 sr rose from c 0 7052 at 850 900 ma to c 0 7085 or higher in the latest neoproterozoic temporal changes at c 800 ma and c 600 ma bracket the range in 87 sr 86 sr values of calcite in grampian appin and lowest argyll group c 0 7064 0 7072 and middle and uppermost argyll group c 0 7082 0 7095 limestones consistent with a rise in seawater 87 sr 86 sr around 600 ma 87 sr 86 sr data are consistent with the sedimentary affinity of the islay subgroup with the underlying appin group and with a possible time interval between deposition of islay and easdale subgroup rocks they indicate that the dalradian as a whole is younger than c 800 ma

relationship of the onset of equatorial f region irregularities with the sunset terminator observed with the equatorial atmosphere radar 1 the relationship between sunset terminators and the onset of radar backscatter plumes associated with equatorial spread f esf observed with the 47 mhz equatorial atmosphere radar from october 2002 to april 2004 is discussed almost all irregularity echoes began to appear at or before sunset time at the altitude of the apex of the geomagnetic field line connected with the observed area and the onset time of more than half of the events corresponded exactly to apex sunset time this tendency should be due to two causes 1 the rapid change of the evening zonal electric field and 2 damping of 3 m scale irregularities by the solar radiation before the apex sunset

thermospheric meridional winds as deduced from ionosonde chain at low and equatorial latitudes and their connection with midnight temperature maximum 1 multipoint ionosonde observation was conducted in southeast asia to study ionosphere thermosphere coupling for this observation three ionosondes were installed along the magnetic meridian at 100 e southeast asia low latitude ionospheric network sealion two of them were at magnetic conjugate points and the third was near the magnetic equator the f layer virtual height h f was scaled from nighttime ionograms obtained from september 2004 to august 2005 close to the solar minimum the height variations at the three locations were used to derive thermospheric winds in the magnetic meridional plane for transequatorial and convergent divergent components with respect to the magnetic equator during northern winter months a prominent 6 hr periodic variation of a transequatorial component was found during northern summer months a diurnal or semidiurnal variation was dominant convergent winds toward the magnetic equator were associated with the occurrence of the midnight temperature maximum at the latitudes between the two conjugate stations as observed by satellite instruments during the solstices however no clear evidence was found of abatement of the wind due to the pressure bulge associated with the midnight temperature maximum

a neoproterozoic multi phase rift sequence the grampian and appin groups of the southwestern monadhliath mountains of scotland the grampian and appin groups of the southwestern monadhliath mountains form the earliest known syn rift sequences of the scottish central highlands they were likely to have formed in an intracontinental setting and represent deposition of mixed clastic and carbonate shallow and deep marine strata the grampian group of the southern monadhliath mountains was deposited during a period of initial basin rifting nw se extension followed by a phase of thermal subsidence syn rift sediments comprise a 2 5 6 km thick turbidite system thermal subsidence brought about the basinward progradation of shallow marine shelf sediments resulting in the infilling of pre existing basin topography the overlying appin group commenced with deposition of a shallow marine sequence alternating between nearshore tidal sand and offshore mud deposition this formed in response to renewed rifting and concomitant subsidence accelerated rifting resulted in localized footwall uplift and erosion while sedimentation continued in the hanging wall areas resultant subsidence perhaps partly thermally driven caused gradual basin widening and produced an onlapping marine sequence there followed a period of progressive clastic deprivation when carbonates were precipitated and at the onset of anoxic conditions deposition of organic muds the fundamental structural elements responsible for the formation of the grampian and appin group basins were also influential in the orogenic evolution of the basin fill half graben fills were deformed to produce regionally extensive folds such as the stob ban craig a chail synform

neoproterozoic chemostratigraphy and correlation of the port askaig glaciation dalradian supergroup of scotland the 13 c of preglacial carbonates beneath the glaciogenic port askaig formation falls from 5 to negative values while least altered 87 sr 86 sr values are close to 0 7067 postglacial cap carbonates of the bonahaven formation begin with negative 13 c carb values jumping sharply to 11 7 near the top which we correlate with excursions above the elbobreen wilsonbreen glaciations of svalbard and putative sturtian not varanger glaciations elsewhere dated at c 720 ma much of the succeeding terminal neoproterozoic is missing in ne svalbard and east greenland raising doubts about their use for global sr and c isotope curves in the neoproterozoic

on the fresh development of equatorial plasma bubbles around the midnight hours of june solstice using the 47 mhz equatorial atmosphere radar ear at kototabang indonesia the nocturnal evolution of equatorial plasma bubbles epbs were examined during the moderate solar activity years 2011 2012 while the evolution of epbs were mostly 86 confined to post sunset hours 1900 2100 lt during equinoxes in contrast the majority of epbs 71 in june solstice found evolve around the midnight hours 2200 0300 lt the mechanisms behind the fresh evolution of summer time midnight epbs were investigated for the first time through sami2 model simulations with a realistic input of background exb drift variation derived from cindi ivm on board c nofs satellite the term by term analysis of linear growth rate of rt instability indicates that the formation of high flux tube electron content height gradient kf steep vertical gradient region at higher altitudes is the key factor for the enhanced growth rate of rt instability the responsible factors are discussed in light of relatively weak westward zonal electric field in the presence of equatorward neutral wind and bottom side recombination around the midnight hours of june solstice the effects of neutral winds and weak westward electric fields on the uplift of equatorial f layer were examined separately using controlled sami2 simulations the results indicate that relatively larger linear growth rate is more likely to occur around midnight during june solstice because of relatively weak westward electric field than other local times in the presence of equatorward meridional wind

peat or no peat why do the rajang and mahakam deltas differ abstract coastal and deltaic holocene peat accumulations around the equatorial island of borneo southeast asia have served as models for economic coal bearing sequences in the stratigraphic record although climatic conditions vegetational communities and sedimentary regimes are comparable peat accumulations are not found on both the western and eastern sides of the island the rajang river delta and coastal plain sarawak east malaysia are covered in areally extensive thick peat deposits that have attained at least a thickness of 13 m in ombrogenous peat domes marudi baram river peat swamp biomass began to accumulate over pleistocene podzols when sea level stabilized 7 5 ka and delta progradation was initiated the mahakam river delta and coastal plain east kalimantan indonesia also began progradation at this time but there is no evidence in any part of the coastal region for peat accumulation rather poorly developed organic rich gleysols occur throughout the delta plain both the rajang river and mahakam river deltas are tidally influenced fine grained systems with a sediment provenance in the central massif sediment transported through the rajang river delta differs in that as much as 60 of the clay minerals deposited in the system are mixed layer i s and expandable k e clays that act to restrict pore water flow in the tidal and overbank deposits that comprise the delta plain these result in the development of an aquiclude above which paludal conditions develop promoting accumulation of organic matter in contrast there is a low proportion of mixed layer and expandable clays transported in the mahakam river system this precludes the development of a stilted water table within the delta allowing for organic matter recycling without peat accumulation the presence of a high proportion of expandable clay minerals on the western side of borneo is a reflection of the weathering and eroding source rocks on this side of the central borneo massif

mudrock dominated fills formed in avulsion splay channels examples from the willwood formation wyoming mudrock dominated channel fills are common features of the fluvial palaeogene willwood formation of wyoming these fills are small on average 30 m wide and 3 m deep and they vary from simple plugs to more lithologically complex fills with internal scour surfaces some fills preserve plant material and others show pedogenic modification all fills are located within metre thick intervals of weakly pedogenically modified mudstones that surround ribbon sandstones the intervals have previously been attributed to channel avulsion the fine grained channel fills are interpreted as crevassesplay feeder channels within these avulsion deposits variation in fill type particularly the presence of pedogenic features appears to be related to floodplain drainage possible factors that influenced drainage were basin position of the fills and palaeogene climate fluctuations although the role of either is not unequivocal in general channel fills with sombre colours and preserved plant detritus indicating poorly drained conditions dominate locations that were proximal to the palaeogene basin axes fills that contain root traces red and yellow brown matrix colours and mottling which indicate pedogenic modification and episodic subaerial exposure of the sediment dominate locations that were more distal to the palaeogene basin axes eocene climate fluctuations particularly episodes of global warming may have been a secondary control on the kind of fill that developed mudrock dominated channel fills have not been described previously from ancient avulsion deposits their common presence in the willwood formation suggests that they are a typical component of avulsion belts and that similar channel fills in other stratigraphic units should be considered with regard to channel avulsion the variety of fills observed in the willwood formation indicates that avulsion belt channels can experience very different fill histories the descriptive details of fills provided here should help in their recognition elsewhere in addition the nature of the channel fill provides important information on ancient drainage conditions in the avulsion belt pedogenically modified channel fills have been recognized only rarely from the stratigraphic record their presence throughout the willwood formation suggests that they should exist in other alluvial successions and may have been overlooked previously they indicate that periods of sediment exposure alternated with episodic influxes of water and sediment in an active avulsion

two from donegal neoproterozoic glacial episodes on the northeast margin of laurentia two glacial episodes the sturtian ca 720 ma and marinoan varangerian ca 590 ma characterize many neoproterozoic successions worldwide in contrast northeast laurentia is typically considered as containing only the latter in scotland and ireland this is represented by the port askaig tillite here we present evidence ice rafted debris for a second younger neoproterozoic glacial event in the dalradian southern highland group of donegal ireland these deposits overlie strata correlative to ca 595 ma rocks in scotland making this heretofore unrecognized glacial episode a marinoan varangerian equivalent in that the port askaig occurs 3 5 km stratigraphically below the southern highland group rocks it is most likely sturtian not marinoan varangerian in age thus the dalradian succession in the irish caledonides contains strata representing both the sturtian and marinoan varanger glaciations

characteristics of large scale wave structure observed from african and southeast asian longitudinal sectors the spatial large scale wave structure lsws at the base of f layer is the earliest manifestation of seed perturbation for rayleigh taylor instability hence found to play a deterministic role in the development of equatorial plasma bubbles epbs except for a few case studies a comprehensive investigation has not been conducted on the characteristics of lsws because of the complexity involved in detecting the lsws particularly in spatial domain in this scenario a comprehensive study is carried out for the first time on the spatial and temporal characteristics of lsws observed in spatial domain over african and southeast asian longitudinal sectors during the year 2011 the observations indicate that these wave structures can be detected a few degrees west of e region sunset terminator and found to grow significantly at longitudes past the sunset terminator the phase fronts of these spatial structures are found to align with the geomagnetic field b lines over a latitudinal belt for at least 5 6 500 600 km centered on dip equator the zonal wavelengths of these structures are found to vary from 100 to 700 km which is consistent with the earlier reports and the epbs were consistently observed when the amplitudes of lsws were grown to sufficient strengths these results would provide better insights on the underlying physical processes involved in excitation of lsws in terms of important roles being played by e region electrical loading and polarization electric fields induced via spatially varying dynamo current due to neutral wind perturbations associated with atmospheric gravity waves

subglacial and proglacial glacitectonic deformation in the neoproterozoic port askaig formation scotland abstract the recognition and interpretation of glacigenic sediments in the ancient rock record has important implications for understanding processes and patterns of climate change diamictite facies from the neoproterozoic port askaig formation scotland have been variously interpreted as evidence for grounded glacier ice mass movements on a glacially influenced submarine slope and subaqueous mass movements in a non glacial environment these contrasting interpretations imply widely differing degrees of ice cover and have contrasting implications for neoproterozoic snowball glaciations in this paper we focus on the great breccia and the disrupted beds two controversial units in the port askaig formation we present evidence that they were formed by the proglacial and subglacial deformation respectively of pre existing shallow marine facies during an advance of grounded ice quaternary examples provide remarkably exact analogues for the great breccia and disrupted beds illustrating the potential value of applying litho and tectono facies models to ancient sedimentary successions

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

some observations regarding the potential effects of doming of tropical peat deposits on the composition of coal beds abstract several important concepts relative to the origin of coal beds can be gleaned from studies of modern domed and planar peat deposits in tropical subtropical settings these are 1 laterally some portions of a single continuous peat deposit may be domed and some portions may be planar 2 domed deposits are most often found to have begun as planar deposits 3 domed formed peat facies may be overridden by planar formed peat facies due to such factors as sea level rise and or increased rate of local and basinal subsidence 4 domed peat facies tend to have less mineral matter and contain fewer inorganic splits than planar facies 5 sulfur intrusion from marine waters can be retarded by doming allowing low sulfur peats to form relatively near to the coastline 6 marine transgression can cause high sulfur marine influenced planar peat facies to override freshwater domed or planar facies resulting in enrichment of the upper parts of these underlying facies in sulfur and ash 7 dome formed peat facies tend to be thicker and more uniform in composition than planar formed facies with dome formed peat facies having the potential to produce the more uniform bright coal types clarains and vitrains and planar formed peat facies often producing duller coal types and or alternating durainic inertinite rich and vitrainic wood derived bands 8 actively developing peat domes in wet settings often exhibit no appreciable increase in inertinitic material toward their tops although the tops of either domed or planar peat deposits can be enriched in inertinitic material if the water table is lowered by either local or regional changes in hydrology or climate

magnetic declination control of the equatorial f region dynamo electric field development and spread f we have carried out a comparative study of the evening prereversal enhancements in the equatorial f region vertical ionization drift velocities vz over fortaleza 4 s 38 w brazil and jicamarca 12 s 77 w peru two magnetic equatorial stations in the american zone the results show profound dissimilarities in the seasonal trends in the times and widths of the vz prereversal peak which reflect in the spread f characteristics as well at the two stations the dissimilarities are shown to be arising mainly from the difference in the magnetic field declination angles that causes differences in the conjugate e region sunset durations and hence in the f region polarization electric field development rates at the two stations

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

vegetation heterogeneity on a late pennsylvanian braided river plain draining the variscan mountains la magdalena coalfield northwestern spain article the spatial heterogeneity and community ecology is reconstructed for late pennsylvanian stephanian b sensu lato vegetation preserved in la magdalena coalfield northwestern spain the 1500 m thick basin fill accumulated rapidly along the margin of the variscan mountains and the principal sedimentary facies comprise the deposits of large braided streams that dissected extensive wetlands containing large lakes quadrat analysis of 93 mostly par autochthonous megafloral assemblages indicates that pteridosperms and ferns dominated communities with three taxa pecopteris spp callipteridium pteridium and neuropteris ovata accounting for 58 of all plant remains sphenopsids and lycopsids were less common but widespread and cordaitaleans were rare at the local scale laterally exposed bedding planes reveal that communities comprised a complex and heterogeneous mosaic of species at the landscape scale ecological gradients are evident from multivariate analyses of quadrats in a facies context pteridosperms dominated marginal wetlands adjacent to steep basin margins a greater proportion of ferns occurred in or adjacent to

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

a mechanism to explain the preservation of leaf litter lenses in coals derived from raised mires abstract leaves and other non woody canopy parts are rarely preserved in coals although the ph of pore waters within peat swamps is usually relatively low 3 5 providing geochemical conditions that would promote preservation after burial shed canopy parts may remain at the air soil interface for periods of up to several months prior to burial by additional organic detritus leaf half life in tropical forests has been reported to range from several weeks to months depending upon species histology during this time of exposure on the forest floor catabolic internal enzymatic fungal bacterial and root degradation as well as saprophagous scavenging act upon the least resistant parts to promote decay into hemic and sapric macerals it is unusual then to find well preserved leaves in peats or coals when such accumulations are encountered either permineralized in coal balls or duripartically preserved in lignites the bedded leaves generally are spatially isolated several explanations have been proposed to account for such fossil lagerstatten that require temporal changes in accumulation or degradation rates neither of these mechanisms is required to account for such accumulations bedded leaves showing minimal evidence of subaerial exposure and degradation have been recovered at depth from a vibracore taken 1 km into the interior of a peat swamp in the rajang river delta sarawak east malaysia evidence is provided to indicate that such accumulations form within peat substrate depressions resulting from the displacement of rootstocks as trees either die and fall over or are blown down in severe storms these localized acidic water filled pools act as a natural buffer to the degradation of fallen canopy parts that accumulate therein

systematic variations in c o and sr isotopes and elemental concentrations in neoproterozoic carbonates in namibia implications for a glacial to interglacial transition abstract we analyzed c o and sr isotopic compositions of neoproterozoic cap carbonates overlying a glacial deposit in namibia to trace environmental changes following the glaciation the three isotopic records showed coherent and phased changes that corresponded to the stratigraphic variation a lower rhythmite unit had three intervals which were distinguished by isotopic variations and mineral type in the basal interval 13 c increased exponentially from a negative value 4 3 pee dee belemnite pdb 13 c values were relatively constant in the middle interval and increased again to positive values in the top interval indicating a phased removal of 13 c depleted carbon from the surface ocean the gradual increase to larger values 6 in the upper stromatolite unit was interpreted to reflect a change in seawater composition resulting from biological activity after environmental recovery from the glacial episode 18 o values and sr isotopic ratios decreased in the basal interval and approached stable values in the middle interval they increased in the upper interval and fluctuated in the stromatolite unit on the basis of geochemical screening criteria for detecting diagenetic alteration of sr isotopes the middle interval of the rhythmite unit with a minimum 87 sr 86 sr ratio of 0 70685 was interpreted to have retained the primary value or to have the least altered sr isotopic composition the basal interval which had ratios 0 718 at its base as high as those of old sialic rocks was interpreted as having altered sr isotopic ratios the high sr isotopic ratios at the base of this interval gradually decreased to near the minimum value at the top of the interval and other isotopic compositions and trace element concentrations showed systematic variations such systematic variations except for the variation in na concentration can be explained by a progressive diagenetic fluid rock interaction alternatively they might reflect a compositional transition from a local transport limited water following the glaciation to global well mixed seawater

giant cross beds in the neoproterozoic port askaig formation scotland implications for snowball earth abstract the neoproterozoic port askaig formation is a thick succession of interbedded diamictite conglomerate sandstone and mudstone that records glacially influenced marine sedimentation in the extensional dalradian basin giant cross beds individual units up to 11 m thick are observed in sandstone at the base of member iii of the port askaig formation the cross bedded sandstones are closely associated with other sandstone diamictite and conglomerate facies and are characterized by both planar and trough shaped foreset laminae with an average maximum dip angle of 14 the cross bedding has compound internal structure and indicates a predominant paleocurrent direction towards the south the sandstone is medium grained well sorted and quartzitic the giant cross beds are interpreted to have formed as a result of the migration of large subaqueous simple and compound dunes in a marine setting based on sedimentological analysis of the sandstone and associated facies as well as the tectonic setting of the port askaig formation the giant dunes are thought to have formed under the influence of tidal currents and indicate open marine ice free depositional conditions the sedimentology of the cross bedded sandstone and its close association with diamictite and conglomerate indicate repeated ice margin advance and withdrawal with periods of both ice free and ice influenced conditions the environmental conditions recorded in these port askaig deposits appear inconsistent with deep freeze or rapid meltback associated with a snowball earth

simple models for the geochemical response of the ocean to climatic and tectonic forcing abstract simple models for the geochemical response of the ocean to periodic forcing are used as a framework to discuss the shortest periods of change resolvable by present analytical precision of elemental or isotopic ratio measurements of the chemical evolution of seawater for chemical properties whose budget is dominated by fluxes into and out of the ocean we show that the geochemical response to changing fluxes is strongly attenuated at periods shorter than the residence time and that the response at these periods is also phase shifted so as to lag the forcing by one quarter cycle the amplitude response as a function of period is used to estimate the periods of forcing resolvable by present analytical precision in measuring the 87sr 86sr and 234u 238u evolution of seawater and we find that the shortest periods resolvable are of the order of 1 myr if variations at periods shorter than this are found we would argue that these are very likely of local as opposed to global origin we illustrate the importance of phase shifts as a function of forcing period by discussing some recently published data that show a high degree of correlation over the last 300 kyr between changes in 87sr 86sr and 18o measured in the same sediment core at first sight this correlation might be taken as good evidence that both 87sr 86sr and 18o are responding to some common climatic forcing but given the long residence time of sr in the ocean sr and o should in fact have different phase shifts relative to any proposed common forcing thus the apparent correlation between 87sr 86sr and 18o over the past several 100 ma is not necessarily an indication that they are responding to a common cause amplitude response curves are also used to place limits on permissible global seawater 234u 238u variations and these are then compared with published data to identify local diagenetic effects application to 187os 186os and u records in seawater detectors is proposed

on postmidnight low latitude ionospheric irregularities during solar minimum 1 equatorial atmosphere radar and gps tec observations in indonesia 1 using the 47 mhz equatorial atmosphere radar ear in west sumatra indonesia 10 36 s dip latitude it is shown that postmidnight irregularities during solar minimum are morphologically different from those detected during solar maximum and are quite similar to those observed with the middle and upper atmosphere mu radar in midlatitudes 29 3 n dip latitude utilizing the rapid beam steering capability of the ear the spatial structure of the postmidnight irregularities is clearly presented for the first time it is found that they usually propagate westward and can be categorized into two types one shows sharp upwelling plumes near local midnight which should not be a mere passage of fossil plasma bubbles the other has successive tilted structures which have the same orientation as medium scale traveling ionospheric disturbances typically observed at midlatitudes we suggest that the convergence of the equatorward thermospheric wind which is believed to be responsible for the midnight temperature maximum may be an important factor to produce a preferable condition for the upwelling plumes in the postmidnight sector the displacement between geographic and magnetic equators may also be important for seasonal longitudinal variation of the postmidnight irregularities