calcified microbial reefs in cambrian series 2 north china platform implications for the evolution of cambrian calcified microbes abstract this study focuses on the microbial reefs of the zhushadong formation cambrian series 2 in shandong province china in order to understand the evolution of calcified microbes in the north china platform during the cambrian series 2 and 3 the microbial reefs occur in a thin unit ca 3 m thick over an area of 1 km 2 they consist of three types of thrombolite based on their mesostructures rimmed grainstone patch and dendritic the thrombolites mainly occur in various coarse grained carbonate facies including crudely stratified oolitic grainstone stromatolitic grainstone and disorganized limestone conglomerate calcified microbes in the thrombolites include epiphyton kordephyton a tubiform microbe bija tarthinia renalcis amgaina and razumovskia the zhushadong thrombolites were formed within a grainstone shoal and experienced repeated burial and exposure the rimmed thrombolite and grainstone patch thrombolite experienced abundant input of carbonate grains forming grainstone patches in contrast the dendritic thrombolite formed solely by calcification of microbes that mainly include epiphyton tarthinia and the tubiform microbe the outer crusts of the rimmed thrombolite were formed by amgaina under high energy conditions the diverse calcified microbes of the zhushadong formation form the earliest assemblage of their type in the north china platform their descendants mostly epiphyton subsequently thrived forming a ca 180 m thick microbialite oolite dominated succession during the cambrian series 3 zhangxia formation although the reefs in the zhushadong formation are much smaller than those of the overlying zhangxia formation their calcified microbes are more diverse this most likely reflects changes in depositional environments e g abundant siliciclastic input and tidal effects vs those of a stable carbonate platform and or global changes within reef environments e g end cambrian series 2 extinction of archaeocyaths and calcified microbes a decrease in diversity of calcified microbes in the north china platform where archaeocyaths were absent may help to account for evolutionary trends in calcified microbes that occurred independently of archaeocyath influence

the analysis of the influence of pumice shape on its terminal velocity 1 pumice particles represent the basic ingredient of many large explosive eruptions and form as a result of magma fragmentation inside the conduit at the onset of eruption fragmental pumices are expelled at high velocity from the crater by the overpressure of gas liberated on explosion the resulting multiphase flow is forced through atmosphere by a variety of transportation mechanisms and pumices eventually decouple from the gas flow settling down to form pyroclastic deposits here we propose new experimental data of terminal velocity together with a quantitative shape analysis of a wide range of pumice particles the resulting model allows predicting the terminal velocity of pumice by means of easily measured particle characteristics with an average error of 12 which compares favourably with previous models

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

a 4000 year lacustrine record of environmental change in the southern maya lowlands peten guatemala a 4000 yr sediment core record from lake salpeten guatemala provides evidence for maya induced forest clearance and consequent soil erosion between 1700 cal yr b c and 850 cal yr a d radiocarbon ages of wood seeds and charcoal support an age depth model with average errors of 110 cal yr relatively low carbonate 18o values between 1300 and 400 cal yr b c coincide with pollen evidence for forest loss consistent with increased surface and groundwater flow to the lake minimum 18o values between 400 cal yr b c and 150 cal yr a d suggest a high lake level as do 14c dated aquatic gastropods as much as 7 5 m above the present lake stage high lake levels resulted from reduced evaporation to precipitation ratios increased hydrologic input caused by anthropogenic deforestation or both the preclassic abandonment 150 a d and early classic late classic boundary 550 a d are marked by relatively high 18o values indicating reduced lake levels oxygen isotope composition increased further coincident with the terminal classic maya demographic decline between 800 and 900 a d this period of high 18o may have been caused by the greater aridity that has been documented in northern yucatan lakes or by decreased hydrologic input to the lake as a consequence of forest recovery reduced soil erosion after 850 cal yr a d coincided with the terminal classic maya demographic decline and permitted forest recovery and resumption of organic sedimentation

dendroid morphology and growth patterns 3 d computed tomographic reconstruction abstract this paper analyzes the growth patterns of dendrolite in the zhangxia formation middle cambrian shandong province china using the technique of 3 d computed tomographic reconstruction dendroids are classified into v dendroids columnar dendroids and arborescent dendroids based on morphological characteristics the means of interconnection between dendroids are classified into trunks nodules shoots and fingers stacking and tiering control the gross morphology and structural framework of dendrolite stacking is a process of vertical growth in which v dendroids create a staircase like structure tiering occurs when a layer of dendroids is covered by sediment and then partially eroded allowing a new layer of dendroids to form a comprehensive blueprint of the structural divisions of dendrolite is presented according to scale being divided into micro meso macro and megastructures the mesostructure which includes individual dendroids and their combined structures is subsequently divided into primary v dendroid secondary columnar and arborescent dendroid and tertiary stair and tier structures and a basic growth model is provided for v dendroids the stages of v dendroid growth are 1 trunk extension and base expansion 2 divergence 3 expansion and convergence followed by repetition of stages 2 and 3 until 4 growth completion followed by the subsequent emergence of a new dendroid by either stacking or tiering this development of systematically ordered structures is suggestive of the reaction of microbial colonies to external environmental conditions

towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications the morphometry of volcanic ash produced by explosive eruptions yields ample information on fragmentation processes e g magmatic vs magma water interactions and on transport and sedimentation mechanisms most previous works on volcanic clast morphometry focused on the apparent 2d projected shape of ash grains here termed apash to infer processes and eruptive styles however textural analyses of ash grains has remained a long and tedious task that made such approaches inappropriate for eruption surveillance duties in this work we show that new technological advances on automated dispersion of granular materials imaged with a camera coupled microscope and enhanced computer capabilities enable fast and high resolution image acquisition of thousands of ash grains that resolve this limitation with a morpho grainsizer designed for such fast and routine measurements we perform a series of apash analyses on selected ash fractions of tephra deposits from known eruptive styles we record the size aspect ratio circularity and convexity of apash images and assess resolution reproducibility minimum population size and total analytical duration and offer recommendations for the reporting of apash data for inter laboratory comparisons to avoid fractal geometry concerns our analyses are carried out at constant size range 250 300 m and optical magnification 5 on 3000 grains per samples collected from homogenized samples results from the andesitic 1999 ongoing eruption of tungurahua volcano ecuador show that ash particles from the moderate 2001 phase are relatively equant and convex in shape while the stronger 2006 subplinian phase produced ash grains with more elongated less circular and less convex apash signatures ash grains from a basaltic scoria cone forming eruption show even more ragged apash characteristics overall our protocol allows obtaining accurate and reproducible morphometric measurements that reveal subtle variations of the morphological signature and the short duration 1 8 hours of the whole analytical process renders high resolution analyses of ash shape achievable for volcano surveillance applications this research ultimately aims to set up a morphometric database of apash results for well defined eruptive styles in order to interpret on a short term basis any apash data from active volcanoes for monitoring purposes

climate change on the yucatan peninsula during the little ice age we studied a 5 1 m sediment core from aguada x caamal 20 36 6 n 89 42 9 w a small sinkhole lake in northwest yucatan mexico between 1400 and 1500 a d oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2 2 and the benthic foraminifer ammonia beccarii parkinsoniana appeared in the sediment profile indicating a hydrologic change that included increased lake water salinity pollen from a core in nearby cenote san jose chulchaca showed a decrease in mesic forest taxa during the same period oxygen isotopes of shell carbonate in sediment cores from lakes chichancanab 19 53 0 n 88 46 0 w and salpeten 16 58 6 n 89 40 5 w to the south also increased in the mid 15th century but less so than in aguada x caamal climate change in the 15th century is also supported by historical accounts of cold and famine described in maya and aztec chronicles we conclude that climate became drier on the yucatan peninsula in the 15th century a d near the onset of the little ice age lia comparison of results from the yucatan peninsula with other circum caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the lia at that time sea surface temperatures cooled and aridity in the circum caribbean region increased

characterization of shape and terminal velocity of tephra particles erupted during the 2002 eruption of etna volcano italy in this paper we present a complete morphological characterization of the ash particles erupted on 18 december 2002 from etna volcano italy the work is based on the acquisition and processing of bidimensional digital images carried out by scanning electron microscopy sem to obtain shape parameters by image analysis we measure aspect ratio ar form factor ff compactness cc and rectangularity rt of 2065 ash particles with size between 0 026 and 1 122 mm we evaluate the variation of these parameters as a function of the grain size ash particles with a diameter of 0 250 mm are subelongate we find that on average particles with a diameter of 0 50 mm are angular using this morphological analysis and an empirical relation between the drag coefficient cd and reynolds number re of wilson and huang earth planet sci lett 44 311 324 1979 we calculate the terminal settling velocities vwh the comparisons between these velocities and those calculated with the formula of kunii and levenspiel fluidization engineering wiley new york pp 97 1969 vkl which considers ash particles as spheres show that vkl are in average 1 28 greater than vwh hence we quantify the systematic error on the spatial distribution of the mass computed around the volcano carried out by tephra dispersal models when the particles are assumed to be spherical

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

early recovery of sponge framework reefs after cambrian archaeocyath extinction zhangxia formation early cambrian series 3 shandong north china abstract reefs dominated by the anthaspidellid sponge rankenella zhangxianensis the calcimicrobe epiphyton and the stem group cnidarian cambroctoconus orientalis together with encrusting microstromatolites occur early in the middle cambrian series 3 late stage 5 of shandong eastern china in the zhangxia formation these in situ components created a tight framework with centimeter scale growth cavities mainly filled by fine grained matrix among them r zhangxianensis and c orientalis mutually attached and locally formed metazoan dominated frameworks these metazoan microbial reefs form thin lenses 505 ma these rankenella reefs indicate recovery of framework building metazoans within 5 million years of the archaeocyath reef decline in structure they resemble archaeocyath reefs as well as early ordovician lithistid sponge microbial reefs having conjoined conical macroskeletons thickly veneered by calcimicrobes and microbial carbonate with largely matrix filled intervening cavities in combination with other sponge microbial reefs reported from australia iran korea and the usa they demonstrate that an anthaspidellid sponge microbial reef consortium was widespread throughout the mid late cambrian

holocene environmental change in the zacapu basin mexico a diatom based record the zacapu basin michoacan mexico is one of a series of internally drained lake basins in the central highlands of mexico the basin has a history of occupation spanning at least 2000 years and before the arrival of the spanish was a major centre for the purepecha culture results are presented of diatom studies from four lacustrine sediment sequences which have holocene radiocarbon dates cemca point 1 cemca point 4 the zacapu core and zacapu section 1 these lie along a transect from the former marsh floor up to the western slopes of the basin zacapu section 1 indicates a deep lake in the basin at some time but the date on this section is thought to be unreliable and the sediments are probably pleistocene in age the other sequences record few major changes in water level in the basin although dry episodes occurred about 4500 bp and more severely about 1000 bp a period of marked catchment disturbance about 7000 to 6000 bp is believed to be the result of volcanic activity on the western flank

the role of bubbles in generating fine ash during hydromagmatic eruptions the abundant fine ash produced in the 2011 subglacial eruption of grimsvotn iceland highlights the fragmentation efficiency of mafic hydromagmatic eruptions which is considerably higher than for comparable dry eruptions ash from the 2011 eruption can be divided into three morphological components vesicular particles shards and dense fragments distinguished by the size and abundance of constituent vesicles we use the vesicle characteristics to define a new shape factor the concavity index which provides an unbiased way to classify individual ash particles as either bubbly vesicular particles and shards or dense the relative proportion of bubbly and dense particles varies systematically with grain size with the proportion of bubbly grains decreasing as the particle size approaches the modal bubble diameter measured bubble volume distributions are similar to those of rapidly quenched pyroclasts from hawaiian fountains and suggest a comparable degassing history during magma ascent yet concordance between the size distributions of ash and of bubbles in the grimsvotn samples stands in contrast to the size distributions in hawaiian fountains where pyroclasts are orders of magnitude larger than individual bubbles we propose that the grimsvotn ash formed by brittle disintegration of vesicular pyroclasts and that fragmentation efficiency was amplified by residual thermal stresses in glass quenched by glacial water the strong control of resulting particle sizes and morphologies by the size and spatial distribution of bubbles demonstrates that the bubble population cannot be ignored when modeling hydromagmatic fragmentation

microbialite morphostratigraphy as a tool for correlating late cambrian early ordovician sequences abstract microbialite morphostratigraphy is a new tool for intrabasinal correlation using diverse microbialite structures morphotypes the recognition of the succession of morphotypes over constrained temporal intervals and broad areas is a function of the complex interactions that operate to create the structure because so many nonlinked variables e g biotic sedimentological physicochemical are involved similar morphotypes do not reoccur over long temporal intervals to demonstrate the technique the upper cambrian lowermost ordovician shelf strata of the great basin united states were correlated using both morphostratigraphy and standard lithostratigraphy six morphozones and one morphosubzone were recognized as were four main lithologic successions because the boundaries between the morphozones and lithologic successions did not coincide it is inferred that the characteristics of the various microbialite structures are not solely controlled by physical factors the principles for establi

retrieval of microphysical and morphological properties of volcanic ash plumes from satellite data application to mt ruapehu new zealand a quantitative analysis of the properties of several mt ruapehu new zealand ash plumes has been performed using multispectral satellite data from the avhrr 2 and atsr 2 instruments the analysis includes identification of the plume from background clouds using the reverse absorption effect in the thermal channels modelling and retrieval of particle sizes determination of the plume height from cloud shadows stereoscopy and meteorological data and estimates of the mass of fine particles radii less than 10 m a new spectral technique for identifying opaque silica rich ash clouds is demonstrated by utilizing the near infrared 1 6 m and visible 0 67 m channels of the atsr 2 and the optical properties of a simple volcanic cloud are presented for use in radiative transfer studies it is found that the ruapehu eruption cloud contained silica rich ash particles with radii generally less than a few micrometres the distribution of fine particles is monomodal with a dominant mode peak of about 3 m radius mass loadings of fine particles are found to be in the range 1 to 7 mg m 3 and are consistent with estimates of mass loadings of volcanic clouds from eruptions of other volcanoes the height of the plume top derived from radiosonde data and plume top temperatures in the opaque regions was found to be between 7 5 and 8 5 km while the plume thickness was estimated to be between 1 5 and 3 km cloud height derived from atsr 2 stereoscopy on a different plume gave heights in the range 5 to 8 km the results of this study provide important information on the optical properties of nascent volcanic eruption plumes this information may prove useful in determining the potential effects of volcanic clouds on local climate and in assessing any hazard to aviation

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

structure and diversity of oldest sponge microbe reefs lower cambrian aldan river siberia the oldest sponge reef is a small early cambrian bioherm at the base of the tommotian stage 535 540 ma in southeast siberia the mainly archaeocyath construction may be a response to turbid conditions cambrocyathellus bowls fused to create a rigid cavernous frame colonized by cryptic archaeolynthus and calcified microbes renalcis in addition to these constructors and binders other reef guilds are present bafflers other archaeocyaths spiculate sponges and hyoliths and dwellers hyoliths mollusks and many others this is the oldest known reef possessing an open skeletal frame structure built by animals and a mixed animal autotroph composition it provides a blueprint for younger phanerozoic reefs

ash sedimentation by fingering and sediment thermals from wind affected volcanic plumes ash fallout and volcanic plume dispersion represent critical hazards for local and global human populations for minutes to years after the onset of an eruption understanding the key processes governing the sedimentation of ash particles is a major challenge in modern volcanology from modeling and risk management perspectives recent experiments predict that sedimentation from eruption clouds rich in fine grained ash can be driven by convective phenomena in the form of 100 m to km scale ash fingers related to the intermittent formation and detaching of ash rich particle boundary layer remote sensing observations of mammatus and cloud veils from numerous eruptions over recent years as well as field observations of spatially discontinuous ash deposits are consistent with this prediction indeed this mode of ash sedimentation is predicted to be the predominant mechanism of fine ash removal for a significant fraction of eruptions in the geological records here we use a novel combination of 3 millimeter wavelength doppler radar observations and time series of optical disdrometer data to characterize for the first time in real time the time varying structure and sedimentation properties of volcanic ash plumes under steady wind conditions as a case study we apply this new method to weak short lived plumes from stromboli volcano 96 of the disdrometer proximal sedimentation data highlight pulsatory phases of increased sedimentation rate that are 20 60 s apart and characterized by particle size distribution variation with bulk concentrations up to 681 mg m3 radar data also record intermittent periods of higher reflectivity i e a factor of 3 in mass concentration inside the ash sedimentation interspersed by 30 to 50 s and interpreted as ash fingers crossing the radar beam from time series of radar signals and ground based disdrometer measurements together with simple analog experiments we develop a conceptual model for intermittent sedimentation from wind affected ash plumes in particular we show that when wind speeds are comparable to or greater than ash settling velocities the dynamics of wind driven rolls in ash clouds can govern the production of gravitational instabilities and the occurrence and timing of ash fingers that form descending sediment thermals in turn this study suggests that ambient wind should affect the maximum size and minimum concentration of ash particles needed to form fingers but also control where and when fingers form at the base of wind drifted ash plumes these novel predictions highlight the need for future work aimed at refining our understanding of ash finger formation under windy conditions from the perspectives of in situ characterization numerical modeling and risk assessment of fine ash dispersal from the most frequent style of eruptions on earth

terminal classic drought in the northern maya lowlands inferred from multiple sediment cores in lake chichancanab mexico we present new density records from sediment cores taken along a depth transect in lake chichancanab mexico the data reveal in great detail the climatic events that comprised the terminal classic drought tcd and coincided with the demise of classic maya civilization between ca 750 and 1050 ad in shallow water cores the tcd is marked by a condensed gypsum horizon in deeper water sections it is expanded and represented by numerous interbedded gypsum and organic rich strata the tcd was not a single two century long megadrought but rather consisted of a series of dry events separated by intervening periods of relatively moister conditions we estimate the tcd occurred between ca 770 and 1100 ad and included an early phase ca 770 870 ad and late phase ca 920 1100 ad the intervening 50 year period ca 870 920 ad was relatively moister each dry phase is represented by multiple gypsum density bands interbedded with organic rich sediment that indicate alternating dry and wet conditions spectral analysis revealed significant periods around 213 50 and 27 years despite uncertainty regarding the ages of these events their pattern is robust and generally consistent with other proxy records under the same climate regime such as the marine cariaco basin off northern venezuela science 299 2003 1731

volcanic ash cloud retrieval by ground based microwave weather radar the potential of ground based microwave weather radar systems for volcanic ash cloud detection and quantitative retrieval is evaluated the relationship between radar reflectivity factor ash concentration and fall rate is statistically derived for various eruption regimes and ash sizes by applying a radar reflectivity microphysical model to quantitatively evaluate the ash detectability by weather radars a sensitivity analysis is carried out by simulating synthetic ash clouds and varying ash concentration and size as a function of the range radar specifications are taken from typical radar systems at s c and x band a prototype algorithm for volcanic ash radar retrieval varr is discussed starting from measured single polarization reflectivity the statistical inversion technique to retrieve ash concentration and fall rate is based on two cascade steps namely 1 classification of eruption regime and volcanic ash category and 2 estimation of ash concentration and fall rate expected accuracy of the varr algorithm estimates is evaluated using a synthetic data set an application of the varr technique is finally shown taking into consideration the eruption of the grinodotacutemsvoumltn volcano in iceland on november 2004 volume scan data from a doppler c band radar which is located at 260 km from the volcano vent are processed by means of the varr algorithm examples of the achievable varr products are presented and discussed

the terminal velocity of volcanic particles with shape obtained from 3d x ray microtomography new experiments of falling volcanic particles were performed in order to define terminal velocity models applicable in a wide range of reynolds number re experiments were carried out with fluids of various viscosities and with particles that cover a wide range of size density and shape particle shape which strongly influences fluid drag was measured in 3d by high resolution x ray microtomography by which sphericity 3d and fractal dimension d3d were obtained they are easier to measure and less operator dependent than the 2d shape parameters used in previous papers drag laws that make use of the new 3d parameters were obtained by fitting particle data to the experiments and single equation terminal velocity models were derived they work well both at high and low re 3 10 2 re 104 while earlier formulations made use of different equations at different ranges of re the new drag laws are well suited for the modelling of particle transportation both in the eruptive column where coarse and fine particles are present and also in the distal part of the umbrella region where fine ash is involved in the large scale domains of atmospheric circulation a table of the typical values of 3d and d3d of particles from known plinian subplinian and ash plume eruptions is presented graphs of terminal velocity as a function of grain size are finally proposed as tools to help volcanologists and atmosphere scientists to model particle transportation of explosive eruptions

characteristics of tephra fall from eruptions at sakurajima volcano revealed by optical disdrometer measurements we investigated the main characteristics of tephra fall from the eruptions at sakurajima volcano in southern kyushu japan by using an optical disdrometer for simultaneous measurement of particle size and fall velocity measurements were carried out for 2 years at one station located 2 5 km south of the active crater this made it possible to detect 76 tephra fall events with the detection rate of the tephra events from these south directed eruption clouds being about 25 from the relationship between particle diameter and fall velocity we were able to estimate morphological parameters of volcanic particles measurements of temporal change in the tephra fall for each minute revealed that both the tephra diameter and fall velocity gradually decrease with time during each event where the ranges of the diameter and velocity for the events with south directed eruption clouds were 0 336 2 04 mm and 1 40 6 24 m s 1 respectively by using temporal changes in the diameter and velocity we estimated travel time and distance for the tephra falling from a release point in the eruption cloud to the station and found a positive correlation between the travel distance and column height for the south directed clouds with a determination coefficient of 0 498 for linear fitting the comparison between tephra data and seismic data revealed that episodic increases in the tephra diameter and fall velocity were correlated with a drastic increase in amplitude of explosion earthquake or tremor these results indicate that disdrometer measurements can provide valuable information about the quantitative features of the tephra fall and are useful for detecting changes in the magnitude of eruption if a number of suitably placed instruments are deployed

isotopic and geochemical evolution of ground and surface waters in a karst dominated geological setting a case study from belize central america abstract analysis of stable isotopes and major ions in groundwater and surface waters in belize central america was carried out to identify processes that may affect drinking water quality belize has a subtropical rainforest savannah climate with a varied landscape composed predominantly of carbonate rocks and clastic sediments stable oxygen 18 o and hydrogen d isotope ratios for surface and groundwater have a similar range and show high d excess 10 40 8 the high d excess in water samples suggest secondary continental vapor flux mixing with incoming vapor from the caribbean sea model calculations indicate that moisture derived from continental evaporation contributes 13 to overhead vapor load in surface and groundwater concentrations of dissolved inorganic carbon dic ranged from 5 4 to 112 9 mg c l and 13 c dic ranged from 7 4 to 17 4 so 4 2 ca 2 and mg 2 in the water samples ranged from 2 163 2 6593 and 2 90 mg l respectively the dic and 13 c dic indicate both open and closed system carbonate evolution combined 13 c dic and ca 2 mg 2 and so 4 2 suggest additional groundwater evolution by gypsum dissolution and calcite precipitation the high so 4 2 content of some water samples indicates regional geologic control on water quality similarity in the range of 18 o d and 13 c dic for surface waters and groundwater used for drinking water supply is probably due to high hydraulic conductivities of the karstic aquifers the results of this study indicate rapid recharge of groundwater aquifers groundwater influence on surface water chemistry and the potential of surface water to impact groundwater quality and vise versa

quantitative shape measurements of distal volcanic ash 1 large scale volcanic eruptions produce fine ash 200 m which has a long atmospheric residence time 1 hour or more and can be transported great distances from the volcanic source thus becoming a hazard to aircraft and public health ash particles have irregular shapes so data on particle shape size and terminal velocities are needed to understand how the irregular shaped particles affect transport processes and radiative transfer measurements in this study a methodology was developed to characterize particle shapes sizes and terminal velocities for three ash samples of different compositions the shape and size of 2500 particles from 1 distal fallout 100 km of the 14 october 1974 fuego eruption basaltic 2 the secondary maxima 250 km of the 18 august 1992 spurr eruption andesitic and 3 the miocene ash hollow member nebraska rhyolitic were measured using image analysis techniques samples were sorted into 10 to 19 terminal velocity groups 0 6 59 0 cm s using an air elutriation device grain size distributions for the samples were measured using laser diffraction aspect ratio feret diameter and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity these measurement values show particle shape differs greatly from a sphere commonly used in models and algorithms the diameters of ash particles were 10 120 larger than ideal spheres at the same terminal velocity indicating that irregular particle shape greatly increases drag gas adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry indicating that particle shapes are highly irregular correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values

particle fallout thermal disequilibrium and volcanic plumes we develop a model of a volcanic eruption column that includes the effects of fallout of pyroclasts and thermal disequilibrium we show that clast fallout with no thermal disequilibrium has only a small effect upon the column however disequilibrium changes column behaviour significantly and can even induce collapse our results may explain the lower plume heights and less widely dispersed fallout of cone forming eruptions contrasted with sheet forming eruptions the model also predicts that the transition from the gas thrust to the convective region in a column results in an inflection in dispersal curves that some features of the stratigraphy common to many fall deposits may result from column velocity structure and that there may exist a region near the volcanic vent in which maximum pyroclast size does not decrease significantly with distance

climate variability on the yucatan peninsula mexico during the past 3500 years and implications for maya cultural evolution climate variability on the yucatan peninsula during the past 3500 yrs is reconstructed from the measurement of 18o in monospecific ostracods and gastropods in a 6 3 m sediment core from lake punta laguna mexico this late holocene record is divided into three periods based on changes in mean 18o values from 3310 to 178514c yr b p period i low mean 18o values indicate relatively wet conditions i e low evaporation to precipitation ratio e p mean oxygen isotopic values increased 178514c yr b p and the interval between 1785 and 93014c yr b p period ii was distinctly drier than the periods before or after the climate during the latter part of period ii was persistently dry with exceptionally arid events centered at 1171 1019 and 94314c yr b p equivalent to 862 986 and 1051 a d this interval of frequent drought was recorded at several other localities in mexico and central america and coincided with the collapse of classic maya civilization following the last arid event 18o values decreased abruptly at 93014c yr b p beginning of period iii signaling a return to wetter conditions that have generally prevailed to the present with the exception of a dry episode centered at 55914c yr b p 1391 a d the paleoclimatic record from punta laguna provides evidence that multi decadal and millennial scale changes ine poccurred on the yucatan peninsula during the late holocene these wet dry episodes may have influenced cultural evolution in mesoamerica

pre holocene and holocene pollen records of vegetation history from the florida peninsula and their climatic implications abstract pre holocene sediments may be found in sinkhole lakers or filled sinkholes in the florida peninsula lake tulane in south central florida yielded a core of 18 5 m under 22 7 m of water the core extends from the present to ca 50 000 yr b p it is age controlled by twenty radiocarbon dates the pre holocene shows alternating peaks of pinus pine dominated and quercus ambrosia oak ragweed dominated vegetation the pine peaks correlate in detail with heinrich events h1 to h5 this demonstrates linkage between continental and oceanic climate events the pine peaks are thought to link with periods of relatively high precipitation and warm gulf water during ice advances oak ragweed peaks are thought to indicate aridity when the gulf and north atlantic surface waters were cooled by melwater from retreating ice sheets lake grizelle is afilled sinkhole with several climatic episodes recorded in pollen counts which are separated from the holocene by a hiatus marked by thick sand it is representative of a category of fossil lakes in florida which promise to contain long and perhaps interglacial pollen records sheelar lake records the end of the wisconsin and the assembling of a species rich forest of mesic trees such as fagus beech close to or south of their present southern geographic limits this forest is believed to be ancestral to the mesic deciduous forest which invaded eastern north america in the next 3000 yr

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

inferred syngenetic textural evolution in holocene cryptic reefal microbialites heron reef great barrier reef australia cryptic microbialites in the heron reef framework occur as crusts of fingerlike microcolumns or branching dendrolites rarely more than 1 cm long microstructure of the most recently growing microbialite surfaces consists of coalesced 3 m scalenohedra that are indistinguishable from previously described mg calcite abiotic cement the transformation from submicrometer anhedral crystallites to 3 m scalenohedra is inferred to have occurred only during active microbialite accretion beneath a biofilm this syngenetic change from primary biologically induced microstructures to microstructures that are indistinguishable from abiotic cement has important implications for the recognition and interpretation of early marine microcrystalline carbonates and cements

climate change and population history in the pacific lowlands of southern mesoamerica core man015 from pacific coastal guatemala contains sediments accumulated in a mangrove setting over the past 6500 yr chemical pollen and phytolith data which indicate conditions of estuarine deposition and terrigenous inputs from adjacent dry land document holocene climate variability that parallels the maya lowlands and other new world tropical locations human population history in this region may be driven partly by climate variation sedentary human populations spread rapidly through the estuarine zone of the lower coast during a dry and variable 4th millennium b p population growth and cultural florescence during a long relatively moist period 2800 1200 b p ended around 1200 b p a drying event that coincided with the classic maya collapse

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

a model for the numerical simulation of tephra fall deposits abstract a simple semianalytical model to simulate ash dispersion and deposition produced by sustained plinian and sub plinian eruption columns based on the 2d advection dispersion equation was applied the eruption column acts as a vertical line source with a given mass distribution and neglects the complex dynamics within the eruption column thus the use of the model is limited to areas far from the vent where the dynamics of the eruption column play a minor role vertical wind and diffusion components are considered negligible with respect to the horizontal ones the dispersion and deposition of particles in the model is only governed by gravitational settling horizontal eddy diffusion and wind advection the model accounts for different types and size classes of a user defined number of particle classes and changing settling velocity with altitude in as much as wind profiles are considered constant on the entire domain the model validity is limited to medium range distances about 30 200 km away from the source the model was used to reconstruct the tephra fall deposit from the documented plinian eruption of mt vesuvius italy in 79 a d in this case the model was able to broadly reproduce the characteristic medium range tephra deposit the results support the validity of the model which has the advantage of being simple and fast to compute it has the potential to serve as a simple tool for predicting the distribution of ash fall of hypothetical or real eruptions of a given magnitude and a given wind profile using a statistical set of frequent wind profiles it also was used to construct air fall hazard maps of the most likely affected areas around active volcanoes where a large eruption is expected to occur

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

paleoenvironmental implications of an extensive maceriate microbialite bed in the furongian chaomidian formation shandong province china abstract this study focuses on the unique occurrence of an extensive microbialite bed 10 20 m thick in the chaomidian formation furongian in shandong province china in order to understand its paleoenvironmental implications the microbialite bed can be traced for over 6000 km2 in area the microbialites are characterized by centimeter to decimeter scale branching maze like constituents maceriae of microbial and muddy sediments with chaotic texture including tabular maceriate microbialite type 1 columnar maceriate microbialite type 2 and columnar chaotic microbialite type 3 within the bed each microbialite unit is generally well correlated for tens of kilometers the entire bed is bounded by limestone marlstone alternation at the base and an erosional surface at the top that is subsequently overlain by a grainstone bed of various thicknesses the microbialite bed formed when the seafloor reached suitable water depth for the microbial growth during sea level rise accompanied with carbonate production the maze like maceria structures formed to acquire a larger surface area under a relatively large input of lime mud the tabular maceriate microbialites initially formed in relatively deep water environments and flourished on broad and flat seafloor whereas the columnar microbialites types 2 and 3 developed under the influence of strong waves and currents the microbialite bed was eroded and terminated by frequent storm events and buried under the reworked grainstone further rise in sea level and increased metazoan activities afterwards limited the resurgence of microbes in the late furongian

growth dynamics of neoproterozoic calcimicrobial reefs mackenzie mountains northwest canada abstract neoproterozoic buildups of the little dal group grew in a deep water epicratonic basin these kilometer scale reefs display aggradational and progradational geometries comparable to those described from phanerozoic reefs four phases of reef growth correspond to four regional shale to carbonate packages in laterally equivalent off reef strata the lower shaly part of each package is interpreted to reflect transgressive to highstand deposition the upper carbonate part of each package reflects carbonate precipitation in the water column as a result of postulated basin restriction and increased salinity during sea level lowstand reefs nucleated at the beginning of the first major transgressive event reefs typically aggraded during transgressive intervals but could also prograde or contract likely depending on the rate of relative sea level rise versus reef growth rate reefs prograded during regressions probably owing to reduction of accommodation space they shed talus at lowstand in response to increased erosion and or progradation over unstable substrates reef growth ended with return of shallow water conditions the overall architecture of aggradation and progradation demonstrates that the neoproterozoic calcimicrobial reef ecosystem was capable of responding to environmental changes in the same way as the more extensively studied ecologically complex and faunally diverse buildups of the phanerozoi

retrieval of volcanic ash particle size mass and optical depth from a ground based thermal infrared camera abstract volcanoes can emit fine sized ash particles 1 10 m radii into the atmosphere and if they reach the upper troposphere or lower stratosphere these particles can have deleterious effects on the atmosphere and climate if they remain within the lowest few kilometers of the atmosphere the particles can lead to health effects in humans and animals and also affect vegetation it is therefore of some interest to be able to measure the particle size distribution mass and other optical properties of fine ash once suspended in the atmosphere a new imaging camera working in the infrared region between 7 14 m has been developed to detect and quantify volcanic ash the camera uses passive infrared radiation measured in up to five spectral channels to discriminate ash from other atmospheric absorbers e g water molecules and a microphysical ash model is used to invert the measurements into three retrievable quantities the particle size distribution the infrared optical depth and the total mass of fine particles in this study we describe the salient characteristics of the thermal infrared imaging camera and present the first retrievals from field studies at an erupting volcano an automated ash alarm algorithm has been devised and tested and a quantitative ash retrieval scheme developed to infer particle sizes infrared optical depths and mass in a developing ash column the results suggest that the camera is a useful quantitative tool for monitoring volcanic particulates in the size range 1 10 m and because it can operate during the night it may be a very useful complement to other instruments e g ultra violet spectrometers that only operate during daylight

cristobalite in volcanic ash of the soufriere hills volcano montserrat british west indies crystalline silica mostly cristobalite was produced by vapor phase crystallization and devitrification in the andesite lava dome of the soufriere hills volcano montserrat the sub 10 micrometer fraction of ash generated by pyroclastic flows formed by lava dome collapse contains 10 to 24 weight percent crystalline silica an enrichment of 2 to 5 relative to the magma caused by selective crushing of the groundmass the sub 10 micrometer fraction of ash generated by explosive eruptions has much lower contents 3 to 6 percent of crystalline silica high levels of cristobalite in respirable ash raise concerns about adverse health effects of long term human exposure to ash from lava dome eruptions

insights on tephra settling velocity from morphological observations in this study we present a systematic and detailed morphological characterization of tephra particles from different eruptions fontana lapilli masaya nicaragua keanak ko i formation kilauea usa recent dome explosions of soufriere hills volcano montserrat and the calculation of their terminal fall velocity tfv as obtained based on different drag prediction models i e wilson and huang 1979 haider and levenspiel 1989 ganser 1993 and dellino et al 2005 in particular particle sphericity and therefore particle surface area is essential for the calculation of tfv of irregular shape particles but is of complex determination various attempts have been proposed according to our results 2d morphological characterization of volcanic particles is a fast and simple application for a wide range of particle size and provides consistent sphericity and settling velocity values 3d scanning also provides a promising tool for lapilli sized tephra 2 cm in contrast gas adsorption derived surface area is not suitable for the calculation of tfv of volcanic particles mostly because it mainly describes the surface contribution of nanometric pores that are not expected to affect significantly tfv and because bulk sample analysis is representative of neither individual particles nor of the whole particle population settling velocities calculated using values of surface area derived from gas adsorption analyses are up to two orders of magnitude lower than the values obtained through 2d analysis in addition our results also show how the influence of particle shape on tfv increases with particle size in particular calculated tfv converges at small particle sizes 3 regardless of the model applied suggesting that the spherical assumption is appropriate for this size fraction discrepancies with the spherical model are within 10 discrepancies with the spherical model increase with particle size up to about 50 and depend on the choice of both the tfv model and the morphological parameterization used in particular the drag prediction model of ganser 1993 is sensitive to the effect of particle morphology on tfv and is well suited for all sizes and reynolds numbers of typical tephra particles finally our results show how individual size categories whole and half are not associated with individual tfv values but with a range of values which increases with class size nonetheless the half system is associated with a smaller standard deviation than the whole system and is therefore more appropriate for the modeling of tephra dispersal in any case for dispersal modeling purposes it is more appropriate to indicate a range of settling velocities for each size class rather than giving an average value

representivity of incompletely sampled fall deposits in estimating eruption source parameters a test using the 12 13 january 2011 lava fountain deposit from mt etna volcano italy the southeast crater sec of mt etna italy is renowned for its high activity mainly long lived eruptions consisting of sequences of individual paroxysmal episodes which have produced more than 150 eruptive events since 1998 each episode typically forms eruption columns followed by tephra fallout over distances of up to about 100 km from the vent one of the last sequences consisted of 25 lava fountaining events which took place between january 2011 and april 2012 from a pit vent on the eastern flank of the sec and built a new scoria cone renamed new southeast crater the first episode on 12 13 january 2011 produced tephra fallout which was unusually dispersed toward to the south extending out over the mediterranean sea the southerly deposition of tephra permitted an extensive survey at distances between 1 and 100 km providing an excellent characterization of the tephra deposit here we document the stratigraphy of the 12 13 january fallout deposit draw its dispersal and reconstruct its isopleth map these data are then used to estimate the main eruption source parameters the total erupted mass tem was calculated by using four different methodologies which give a mean value of 1 5 0 4 108 kg the mass eruption rate mer is 2 5 0 7 104 kg s using eruption duration of 100 min the total grain size tgs distribution peaked at 3 phi ranges between 5 and 5 phi and has a median value of 1 4 phi further for the eruption column height we obtained respective values of 6 8 13 8 km by using the method of carey and sparks 1986 and 3 4 0 3 km by using the methods of wilson and walker 1987 mastin et al 2009 and pistolesi et al 2011 and considering the mean value of mer from the deposit we also evaluated the uncertainty and reliability of tem and tgs for scenarios where the proximal and distal samples are not obtainable this is achieved by only using a sector spanning the downwind distances between 6 and 23 km this scenario is typical for etna when the tephra plume is dispersed eastward i e in the prevailing wind direction our results show that if the analyzed deposit has poorer sample coverage than presented in this study the tem 3 4 107 kg is 22 than the tem obtained from the whole deposit the lack of the proximal 6 km deposit may cause more significant differences in the tgs estimations

environmental change in northern belize since the latest pleistocene cores from the new river lagoon in belize have been analysed using a range of palaeolimnological proxies to reconstruct change since the latest pleistocene the combination of diatom and stable isotope analyses supported by mineralogical and major element data indicate that the new river lagoon has been a freshwater system throughout the period of record for most of this time the lagoon has been hydrologically open but there are indications that it may have become closed in the latest pleistocene or very early holocene this may have been associated with a drier climate and lower sea level mid holocene records are consistent with those from elsewhere in the region indicating a stable and moist climate the late holocene was marked by greater variability but there is no clear evidence of any drying in the late classic coincident with the maya collapse ca ad 900 our results indicate that the continuity of occupation at the maya site of lamanai on the shores of the new river lagoon is consistent with continued access to freshwater during periods of regional climatic variability the importance of conditions at individual sites when considering both system response and human vulnerability to climate change is emphasised copyright 2009 john wiley sons ltd

in situ terminal settling velocity measurements at stromboli volcano input from physical characterization of ash ash particle terminal settling velocity is an important parameter to measure in order to constrain the internal dynamics and dispersion of volcanic ash plumes and clouds that emplace ash fall deposits from which source eruption conditions are often inferred whereas the total particle size distribution psd is the main parameter to constrain terminal velocities many studies have empirically highlighted the need to consider shape descriptors such as the sphericity to refine ash settling velocity as a function of size during radar remote sensing measurements of weak volcanic plumes erupted from stromboli volcano in 2015 an optical disdrometer was used to measure the size and settling velocities of falling ash particles over time while six ash fallout samples were collected at different distances from the vent we focus on the implications of the physical parameters of ash for settling velocity measurements and modeling two dimensional sizes and shapes are automatically characterized for a large number of ash particles using an optical morpho grainsizer morphologi g3 manually sieved ash samples show sorted relatively coarse psds spanning a few microns to 2000 m with modal values between 180 and 355 m although negligible in mass a population of fine particles below 100 m form a distinct psd with a mode around 5 20 m all size distributions are offset compared to the indicated sieve limits accordingly we use the diagonal of the upper mesh sizes as the upper sieve limit morphologically particles show decreasing average form factors with increasing circle equivalent diameter the latter being equal to 0 92 times the average size between the length and intermediate axes of ash particles average particle densities measured by water pycnometry are 2755 50 kg m 3 and increase slightly from 2645 to 2811 kg m 3 with decreasing particle size the measured settling velocities under laboratory conditions with no wind 3 6 m s 1 are in agreement with the field velocities expected for particles with sizes 460 m the ganser 1993 empirical model for particle settling velocity is the most consistent with our disdrometer settling velocity results converting disdrometer detected size into circle equivalent diameter shows similar psds between disdrometer measurements and g3 analyses this validates volcanological applications of the disdrometer to monitor volcanic ash sizes and settling velocities in real time with ideal field conditions we discuss ideal conditions and the measurement limitations in addition to providing sedimentation rates in situ calculated reflectivities can be compared with radar reflectivity measurements inside ash plumes to infer first order ash plume concentrations detailed psds and shape parameters may be used to further refine radar derived mass loading retrievals of the ash plumes

latest middle cambrian metazoan reef from northern iran middle and late cambrian reefs were built mainly by cyanobacterial communities a few reefs with a metazoan as well as an algal component however are known from this interval a middle cambrian reef formed primarily by spicular demosponges is described here from the mila formation in the elburz mountains northern iran the reef is enclosed within calcareous grainstones which contain terminal middle cambrian late mayan trilobites the mila formation reef was constructed by sponges of the family anthaspidellidae and bacterial algal sheaths and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges the reefal community is typical of subsequent reefal communities of early middle ordovician age the ordovician examples differ only by the incorporation of additional metazoan elements

cambrian series 3 carbonate platform of korea dominated by microbial sponge reefs abstract metazoans have been considered as negligible components of cambrian series 3 and furongian microbial dominated reefs in contrast to their presence in earlier terreneuvian cambrian series 2 microbial archaeocyath reefs however recent discoveries of sponges in cambrian series 3 furongian reefs of australia china iran usa and korea have raised question regarding their contribution in terms of carbonate platform development which have never been assessed this study examines cambrian series 3 deposits of the daegi formation korea to elucidate this question the 100 m thick middle part of the daegi formation is dominated by boundstone facies which occupies 45 of the study interval as well as bioclastic wackestone to packstone bioclastic grainstone and ooid packstone to grainstone facies the daegi reefs are primarily thrombolitic in composition with 90 n 26 29 of the reefs containing an average of 9 sponges in aerial percentage calculated from thin sections lithistid sponges composed of peloidal fabrics some desma spicules and spicule networks commonly occupy the interstitial space in microbial clusters are encrusted by mesoclots and epiphyton and are surrounded by micrite subordinate non lithistid demosponges occur within clusters of microbial elements the middle daegi formation can be largely subdivided into shoal environment dominated by grainstone to packstone facies and shallow subtidal platform interior environment located behind shoal with wackestone to packstone facies the microbial sponge reefs mainly developed around platform interior as patch reefs the current study indicates that metazoans in the form of lithistid and non lithistid demosponges are nearly ubiquitously incorporated in daegi reefs and contributed greatly to the formation of microbial sponge reefs as well as carbonate platform during the time study of these microbial sponge reefs and their distribution within the carbonate platform may help us to understand how carbonate sedimentary environments responded to the extinction of archaeocyaths

formative mechanisms depositional processes and geological implications of furongian late cambrian reefs in the north china platform abstract the cambrian series 3 furongian successions of the north china platform contain various microbial metazoan and microbial reefs this study focuses on furongian reefs of the platform in order to understand formative processes and the evolution of the reefs during cambrian epoch 3 and the furongian three types of furongian reefs were differentiated in the shandong region china maceriate reefs columnar stromatolitic reefs and small scale microbial reefs maceriate reefs show dm to m scale domal or flat bedded geometry and consist of cm scale maze like maceria structures made of siliceous sponges and microbial components microstromatolites girvanella and tarthinia columnar stromatolitic reefs are characterized by stromatolite columns of 10 100 cm in height and 5 50 cm in diameter they consist dominantly of girvanella with less conspicuous poorly preserved sponge spicule networks small scale microbial reefs commonly show cm to dm scale domal macrostructures and were constructed mainly by calcimicrobes girvanella and renalcis these three types of furongian reefs were deposited in various shallow marine settings in response to relative sea level changes the furongian reefs are markedly different in terms of macro and micro fabrics from the cambrian series 3 reefs that are dominated by thrombolites and dendrolites and were constructed mainly by epiphyton in the shandong region this difference is also recognized in the beijing region ca 500 km away the abrupt transition from the cambrian series 3 type to furongian type reefs coincidently with a decrease in calcified microbe diversity was most likely due to global euxinic oceanic conditions and a possible eustatic sea level drop rather than the highly diachronous platform wide drowning event i e drowning of the cambrian series 3 carbonate platform the abundant occurrence of sponge spicule networks in the furongian reefs suggests that metazoan reef builders i e sponges resurged and became actively involved in the reefal systems prior to the great ordovician biodiversification event this study may provide an important basis for further investigation into the evolution of reefal systems during the middle to late cambrian when metazoan reef builders were known to be scarce

recent history of sediment deposition in marl and sand based marshes of belize central america there are two contrasting types of wetlands in belize marl and sand based marshes we measured accumulation rates of sediment in six cores from marl and sand based marshes of northern belize and compared biogeochemical characteristics to assess recent wetland history f1850 to present sediment depth increments were analysed for bulk density loi nutrients c n p s ca mg k and na and snail shell density and species diversity cores were dated using 210 pb and a constant rate of supply model unsupported 210 pb inventories of the cores ranged from 6 16 to 8 92 pci cm 2 marl based marshes showed the maximum peak of 210 pb activity from 4 to 10 cm below the sediment surface 210 pb peaks corresponded with the bottom of a marl layer containing chlorophyll a and we suggest that this relationship reflects the high growth and decomposition rates of cyanobacterial mat inorganic carbon ca mg k na s and pb contents and accumulation rates were much greater in the marl based marshes than in the sand based marshes average dry mass accumulation rates in the six marshes ranged from 113 to 572 g m 2 year 1 over the past 100 years average linear sedimentation rates during the last 100 years in the two types were not significantly different 0 93 and 1 08 mm year 1 respectively increased sediment accumulation by human activities such as soil washout from adjacent roads was recorded in a sand based marsh near roads sediment cores in the marl based marshes display changes of marsh vegetation apparently caused by water level changes the vegetation change occurred at the end of the 1800s and the beginning of 1900s and is represented by a band of dark peat in otherwise marl dominated sediments overall the sediment cores show that conditions were relatively undisturbed by human activities in the recent past d 2002 elsevier science b v all rights reserved

tephra sedimentation during the 2010 eyjafjallajokull eruption iceland from deposit radar and satellite observations the april may 2010 eruption of eyjafjallajokull volcano iceland was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in iceland and caused a global wide interruption of air traffic eruptive activity during 4 8 may 2010 was characterized based on short duration physical parameters in order to capture transient eruptive behavior of a long lasting eruption i e total grainsize distribution erupted mass and mass eruption rate averaged over 30 minute activity resulting 30 minute total grainsize distribution based on both ground and msg seviri satellite measurements is characterized by mdphi of about 2 phi and a fine ash content of about 30wt accumulation rate varied by two orders of magnitude with an exponential decay away from the vent whereas mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4 5 phi between 20 56 km associated mass eruption rate is in between 0 6 1 2 x 10 5 kg s 1 in situ sampling showed how fine ash mainly fell as aggregates of various typologies about 5 to 9 wt of the erupted mass remained in the cloud up to 1000 km from the vent suggesting that nearly half of the ash 7 phi settled as aggregates within the first 60 km particle sphericity and shape factor varied between 0 4 and 1 with no clear correlation with size and distance from vent our experiments also demonstrate how satellite retrievals and doppler radar grainsize detection can provide real time description of the source term but for a limited particle size range

the impact of particle shape on fall velocity implications for volcanic ash dispersion modelling abstract modelling atmospheric volcanic ash dispersion is a critical tool in mitigating the impact of large explosive eruptions it is also useful for understanding and reconstructing past events most atmospheric dispersion models include a sedimentation velocity term that is sensitive to the physical properties of the particle but many do not use particle shape as an input parameter instead particles are assumed to be spherical there are many empirical and semi empirical shape dependent drag laws we measure the velocity of scaled analogue particles over the range of flow conditions anticipated for volcanic ash dispersion to test published formulae against an independent dataset we use a semi empirical formula we determined to be accurate for non spheres to investigate the sensitivity of the modelled transport of an ash cloud to particle shape using the atmospheric dispersion model name and a shape parameter we measure for non spherical ash particles from katla volcano iceland we find that model particle trajectories are sensitive to particle shape for particles 1 3 m diameter the sedimentation velocity of smaller particles is low compared to atmospheric vertical velocities sensitivity to shape increases with size such that 100 m particles can travel 44 further from the source when they are highly non spherical sphericity 0 5 despite the sensitivity of the fall velocity of large particles to their shape however forecasts of distal ash concentration using particle size distributions of 0 1 100 m and 0 1 250 m show relatively good agreement between a spherical and non spherical case for the first 36 h after an eruption the vertical structure of an ash cloud is more sensitive to particle shape than the horizontal extent model particle trajectories are also sensitive to particle size and we find a discrepancy between different particle size parameters for non spherical ash particle long axis l used in cryptotephra studies was on average twice the equivalent volume sphere diameter dv used in dispersion modelling for tephra samples from katla volcano iceland this discrepancy in size measurements could explain the observed travel distance of large distal cryptotephra shards

rain field and reflectivity vertical profile reconstruction from c band radar volumetric data operating a meteorological radar is generally a challenging task when in presence of a significant beam blockage as in complex orography apart from enhanced ground clutter mountainous obstructions of the radar beam can significantly reduce the radar visibility and thus its monitoring capabilities self consistent adaptive techniques to reconstruct vertical profiles of reflectivity vpr and near surface rain rate fields from high elevation reflectivity bins are here proposed compared and tested for ranges up to 60 km the methodology is based on statistical estimators trained by a large reflectivity volumetric datasets classified into stratiform and convective rain regimes and resampled onto a uniform cartesian grid by means of a modified cressman technique for what concerns reflectivity vertical profiles two methods respectively named statistical nonlinear reconstruction nsr and neural network reconstruction nnr are considered the nsr method is based on the principal component analysis applied to the radar dataset in order to extract significant reflectivity profile variance a retrieval technique based on a nonlinear multiple regression scheme is then used to infer near surface reflectivity from available high altitude echoes at a given range the nnr is based on a three layer artificial neural network trained by means a feedforward backpropagation algorithm for what concerns the near surface rain retrieval besides a power law reflectivity rain rate zr approach a three layer neural network technique is also set up in order to estimate surface rain rate from reconstructed vpr the proposed reconstruction techniques are here illustrated by using volumetric data acquired by the c band doppler single polarization radar operated in l aquila italy a case study related to a rainfall event that occurred during fall 2000 is discussed using a test area within 60 km from the radar site and simulating the presence of beam obstructions a comparison of nsr and nnr with conventional area average reconstruction techniques shows that the percentage improvement of both nsr and nnr approaches is significant both for the error bias by 30 to more than 50 depending on altitude and variance by 10 to more than 20 a sensitivity test indicates that the vpr reconstruction procedure is fairly robust to missing data especially in terms of error bias the comparison of estimated radar rainfall with rain gauge data measurement is also illustrated the mean field bias closer to its optimal value and an error variance much smaller is obtained when neural network techniques are applied than with conventional zr methods for both techniques of reconstruction with respect to the latter the obtained improvement is more than 40 in terms of root mean square error and is comparable when estimating near surface rain rate using either nsr or nnr methods to reconstruct the reflectivity vertical profiles limitations potential and future developments of the proposed adaptive reconstruction techniques are finally discussed

holocene palaeosalinity in a maya wetland belize inferred from the microfaunal assemblage abstract a 5 4 m sequence of peat and marl overlying a basal clay in a northern belize wetland was studied to assess salinity changes over the past 7000 yr the distribution of ostracods gastropods and foraminifers revealed initially freshwater conditions in a terrestrial wetland changing to at least mesohaline conditions by about 5600 yr b p the mesohaline conditions corresponded to the formation of an open water lagoon and precipitation of a lacustrine marl that was contemporaneous with rapidly rising sea level in the area a mangrove peat filled the lagoon by 4800 yr b p probably as a result of increasingly shallow waters as sea level rise slowed and marl precipitation continued a new lagoon began to form sometime after 3400 yr b p freshwater ostracods and gastropods found in the marl of this lagoon suggest that it formed under near limnetic conditions freshwater input likely resulted from massive deforestation by the maya that began by 4400 yr b p subsidence of the mangrove peat likely permitted the formation of a lagoon a peat has filled the lagoon since at least 500 yr b p