the bucobello 322 ka fossil bearing volcaniclastic flow deposit in the eastern vulsini volcanic district central italy mechanism of emplacement and insights on human activity during mis 9 abstract we present a multidisciplinary study of a fossiliferous site located in the vulsini volcanic district on the western side of the tiber river valley north of rome highlighting the peculiar geologic factors that contributed to the origin and preservation of an outstanding archaeological record testifying of the early human frequentation in this region mighty explosive eruptions since at least 500 ka affected the investigated area eventually culminating in the formation of the huge bolsena caldera tectonic deformation accompanying volcanic activity caused large fault displacements shaping the ground surface and contributing to route the path and possibly to trigger the catastrophic emplacement of volcaniclastic flows a sedimentary trap originated by fault scarp cutting through a streambed was likely the cause for the large accumulation of bones and stone artifacts ripped up and carried by a volcaniclastic flow at 322 ka the analysis of the fossil assemblage reveals both gnawing traces by carnivores and cut marks from the percussion tools employed by humans to butch the carcasses however the occurrence of retouched and unretouched blanks within the lithic assemblage also testifies for provenance from a wider area of human activity which included hunting and scavenging probably at a nearby butchering site

continental carbonates from itaborai formation in southeastern brazil abstract since the discovery of the massive south atlantic hydrocarbon reservoirs pre salt the interest in these terrestrial carbonates has increased in brazil few examples of continental carbonates are known and solely the occurrence described in this study can be recognized as continental thermal carbonate or travertine the occurrence is part of the sedimentary sequence of the itaborai formation deposited in itaborai basin located in rio de janeiro state about 60 km from the city of rio de janeiro the basin dates back to the paleocene due to its vertebrate fossil content which can be found in a small half graben basin 1 5 km 0 5 km despite the small size of the basin it represents a huge source of geological information for its diverse fossil assemblage the occurrence of travertine and the exposition of alkaline dyke most of the studies regarding the basin are related to the extensive fossil community from the lake fill facies succession which are not directly related to the travertine deposition the present study conducted a sedimentological investigation applying petrography facies association and isotope analysis as its methodology as a result four distinct facies associations were described thermal springs alluvial palustrine lacustrine and fissural sedimentation succession allowed the study to recognize sedimentation and tectonic relationship the origin of the thermal activity is probably related to the tectonic pulses of the hemi graben system so in these conditions two different contexts for travertine deposition associated to the flexural and active borders of the basin were established the petrography exhibited shrubs textures with remarking crystalline quality indicating a major abiotic influence during the process of precipitation the stable isotope ratios provided contrasting results against those expected for a thermal carbonate signature but not so different from those expected for meteoric carbonate signature indicating a mixture of both processes

petrography and genesis of spicular and columnar geyserite from the whakarewarewa and orakeikorako geothermal areas north island new zealand domal masses of geyserite which surround many geyser vents in the whakarewarewa geothermal area are formed largely of spicules spicule columns and shrub columns the non branching spicules and the branches of branching spicules individually up to 3 cm high and 1 mm diameter have a laminated core encased by siliceous cortex silicified microbes are rare in the core but common in the cortex silicified microbial mats and pseudodendrites are found in the crevices between neighbouring spicules shrub columns up to 5 cm high and 1 5 cm in diameter are formed of opal a that was precipitated around a three dimensional branching shrub like microbial structure the shrub branches which are hollow with scalloped walls do not contain any evidence of the original microbes or minerals that formed them silicified microbial mats are present between the columns microbial boring and etching by acidic steam led to local diagenetic degradation of these columns in the geyserite mounds at whakarewarewa spicules and spicule columns are common whereas shrub columns are rare interbedding and intercalation of spicular geyserite with shrub columnar geyserite indicate however that these different morphologic entities probably formed under similar environmental conditions on the mounds around the geyser vents petrographic evidence shows that the spicules spicule columns and shrub columns grew through a combination of biotic and abiotic processes

the cryptotephra record of the marine isotope stage 12 to 10 interval 460 335 ka at tenaghi philippon greece exploring chronological markers for the middle pleistocene of the mediterranean region abstract precise chronologies that allow direct correlation of paleoclimate archives are a prerequisite for deciphering the spatiotemporal characteristics of short term climate variability such chronologies can be established through the analysis of tephra layers that are preserved in the respective sedimentary archives here we explore the yet untapped tephrochronological potential of the eastern mediterranean region for the middle pleistocene specifically for the interval spanning marine isotope stages mis 12 10 460 335 ka high resolution cryptotephra analysis was carried out on peat cores spanning the mis 12 10 interval that have been recovered from the iconic climate archive of tenaghi philippon ne greece eighteen primary cryptotephras were identified and major and trace element analyses of single glass shards from all cryptotephras were performed in order to correlate them with their eruptive sources the results suggest origins from both italian and aegean arc volcanoes specifically one cryptotephra layer could be firmly correlated with the cape therma 1 eruption from santorini which makes it the first distal tephra finding for this eruptive event while eight further cryptotephras could be tentatively correlated with their volcanic or even eruptive sources the provenance of another nine cryptotephras as yet remains unknown the relatively large number of cryptotephras that could not be assigned to specific volcanic sources and eruptive events reflects the still considerable knowledge gap regarding the geochronology and geochemistry of proximal tephra deposits from the middle pleistocene of the central and eastern mediterranean regions due to the lack of well dated middle pleistocene eruptions we provide age estimates for all cryptotephra layers identified in the mis 12 10 interval at tenaghi philippon based on high resolution pollen data from the same cores while eight of the identified cryptotephras were deposited within mis 12 438 427 ka one cryptotephra was deposited at the onset of mis 11 419 ka five cryptotephras during the younger part of mis 11 391 367 ka and four cryptotephras during mis 10 359 336 ka the high number of cryptotephras from multiple sources as recorded in the mis 12 10 interval at tenaghi philippon highlights the key role of this archive for linking tephrostratigraphic lattices for the middle pleistocene of the central and eastern mediterranean regions

external modulation of volcanic activity summary time and again records of seismovolcanic activity that show a diurnal and semi diurnal modulation have been related to the earth s tidal stress field as an external triggering mechanism several seismic data sets from different volcanoes are examined including stromboli volcano italy mt ruapehu new zealand and merapi and batur indonesia where in some cases weather data are also incorporated a comparison with theoretical body tides in the spectral domain reveals strong evidence against a correlation between seismovolcanic activity and tidal stress however other parameters such as temperature and barometric pressure show the same diurnal and semi diurnal modulation and are therefore candidates for a possible external modulation of volcanic activity several mechanisms are discussed for stromboli a clear correlation between volcanic activity and barometric pressure is shown

oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico an integrated sequence stratigraphic study based on outcrop core and wireline log data documents the combined impact of cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern gulf of mexico the diverse facies and abundant data of the comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting cretaceous platform development regional cross sections across the shoreline to shelf margin profile provide a detailed record of mixed carbonate siliciclastic strata for the hauterivian to lower campanian stages ca 136 to 80 ma the study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes three second order supersequences comprised of eight composite sequences are recognized in the valanginian barremian the aptian albian and the cenomanian campanian the valanginian barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting as well as variable rates of mid ocean ridge volcanism the aptian albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b the cenomanian campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d after which the platform evolved to a deep subtidal system consisting of anoxic dysoxic shale and chalk in the time surrounding oceanic anoxic event 2 each period of oceanic anoxia is associated with composite sequence maximum flooding termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain dominated facies and shallow subtidal to intertidal environments because they are products of eustacy and global oceanographic processes the three supersequences and most composite sequences defined in the south texas passive margin are recognizable in other carbonate platforms and published eustatic sea level curves

stratigraphic architecture palaeogeography and sea level changes of a third order depositional sequence the late turonian early coniacian in the northern iberian ranges and central system spain abstract this paper reports a high resolution stratal palaeogeographical and quantitative analysis of a late turonian early coniacian carbonate ramp the northern iberian ranges and its siliciclastic coastal margin the central system the analyzed succession comprises a complete 3rd order depositional sequence with a shelf margin wedge a transgressive systems tract and a highstand systems tract based on the existence of a subaerial exposure evidences and early diagenetic overprints b stratal relationships onlap offlap toplap regarding underlying and overlying sequences and c changes in the vertical facies evolution the depositional sequence was bounded by two major sequence boundaries these indicate that a major fall in relative sea level occurred in these boundaries the comparative study of the internal stratal surfaces and the vertical facies succession allowed the identification of superimposed higher order depositional parasequences sets and parasequences 4th to 5th order which record short term changes in the relative sea level thus when vertical facies trends in the parasequences are arranged in the framework of a parasequence set a clearer palaeogeographic picture is obtained and palaeogeographic maps can more clearly show the evolutionary trend of the basin each parasequence set was composed of a basal lowstand transgressive systems tract in turn composed of fringing siliciclastic shoreface deposits and offshore muds older sequences were partially exposed further landwards the sedimentation of these sands resulted in the progradation of the coastal systems during times of low relative sea level during which the basal parasequence set boundary was also generated subsequent transgression remobilised underlying lowstand sands the early highstand was composed of carbonate sediments in platform areas and mixed siliciclastic carbonate sediments landwards separated by a narrow fringe of muddy marl offshore sediments the late highstand showed a progressive shallowing trend with carbonate littoral and tidal sediments covering broad areas of the basin and lagoon facies were restricted to the northern outcrops during late highstand underlying transgressive systems tract and older highstand deposits were exposed landwards sea level and accommodation curves have been obtained from paleogeographical sedimentological and sequence stratigraphical data the mean sea level curve for the entire 3rd order sequence shows a rise of the sea level and then an overall stillstand but accommodation curve shows a positive trend along the sequence the 3rd order sea level cycle has a mean amplitude of 52 m and high frequency cycles have amplitudes of 20 40 m 4th order and about 1 5 4 m 5th order the mean final rise in the sea level 46 6 m is quite similar to the total accommodation deduced from fischer plot 45 75 m the sea level cycles are considered to be eustatic in origin and driven by orbital forcing in the milankovitch band based on the estimated 4th order 400 kyr and 5th order cycle lengths 80 kyr

pumice fall deposits of the western vulsini volcanoes central italy abstract widely dispersed pyroclastic fall deposits are prominent among the volcanic products of the western part of the vulsini volcanic district central italy in this paper we describe major pumice fall deposits in the area that correlate to the early activity of the latera volcanic complex 0 3 0 2 ma they represent excellent stratigraphie markers for a wide area mostly extending west and south of the present latera caldera pumice fall deposits lower b and upper b are closely associated with major pyroclastic flow units of the canino eruptive unit pumice fall c caps the canino products without relevant time hyatus pyroclastic falls d and e the latter part of the minor stenzano explosive eruption belong to the stratigraphic interval between canino and farnese eruptive units pumice fall f is part of the initial products of the farnese eruptive sequence we present detailed stratigraphy depositional features vertical and lateral variations of grain size componentry and chemical composition in individual fallout beds source areas as inferred from thickness and maximum pumice and lithic clast size distributions are located in the area of the present day latera caldera tentative estimates of volume column height and magma discharge rate indicate moderate large to large plinian eruptive events

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

unusual mixed silica carbonate deposits from magmatic hydrothermal hot springs savo solomon islands abstract the volcanic island of savo solomon islands hosts an active hydrothermal system discharging unusual alkaline ph 7 8 sulphate rich chloride poor fluid with variable admixtures of ca mg hco 3 rich fluid hot springs and their outflow streams precipitate a variety of deposits including travertine silica sinter and unusual mixed silica carbonate rocks travertine fabrics are dominated by ray crystal calcite associated with rapid abiotic precipitation from a supersaturated solution sinter is produced by evaporation of thermal waters and downstream samples contain preserved traces of micro organisms which potentially acted as templates for precipitation trace element chemistry of sinters and travertines includes anomalously high levels of te indicating a magmatic origin for a component fluid in the hydrothermal system springs are close to or at saturation with both calcite and amorphous silica increased contributions from the ca mg hco 3 end member favours calcite formation this fluid is of low temperature origin and as such is favoured by high rainfall mixed samples show cyclical changes between silica and carbonate precipitation potentially as a result of seasonal variation in rainfall supplementary material a spreadsheet of water and deposit chemical analyses is available at www geolsoc org uk sup18495

chemical evolution of thermal springs at arenal volcano costa rica effect of volcanic activity precipitation seismic activity and earth tides arenal volcano in nw costa rica central america has been active during the last 37 years however only relatively low temperature springs have been identified on its slopes with temperatures less than around 60 c the springs are clustered on the ne and nw slopes of the volcano close to contacts between the recent and older volcanic products or at faults that intercept the volcano this volcano is located in a rain forest region with annual rainfall averaging around 5 m during the last 15 years the temperature and chemical composition of 4 hot springs and 2 cold springs have been monitored approximately every 3 months in addition two more thermal sites were identified recently and sampled as well as two boreholes located on a fault ne of the volcano scatter plots of chemical species such as cl and b suggest that the waters in these discharges belong to the same aquifer with a saline end member similar to rio tabacon at the beginning of the study period 1990 and the deeper borehole b 2 in 2004 the waters of quebrada bambu and quebrada fria represent a more dilute end member both long term over the 15 years and short term or seasonal decreases in concentration and steady or decreasing temperature are noted in nw springs springs located at the ne show increasing temperatures and ion concentrations except for bicarbonate that has decreased in concentration for all the springs this behavior is likely associated with a shallow source for the solutes and heat for this aquifer to the nw the early lavas and pyroclastic flows have been cooling down decreasing the contribution of leaching products to the infiltrating waters to the ne pyroclastic flows to the n during the last decade are contributing increasing concentrations of solutes and heat throughout water infiltration and circulation within the faults and the surficial drainage that has a ne regional trend for the short term or seasonal variations concentrations of chemical constituents decrease when precipitation increases however correlations between concentrations and the number of seismic events per month and the modeled vertical tidal acceleration are also observed the intrinsic periodic behavior of all these variables influenced by the earth s rotation can complicate the interpretation of the chemical changes at hot springs for example variations in atmospheric pressure can affect the degassing and seismic tremor of a volcano as well as the rate of precipitation frequent monitoring and understanding of these variations is essential at every volcano if we want to use the variations in chemical composition of hot springs in volcanic monitoring

cyanobacteria associated with hot spring travertines cyanobacteria are the major oxygenic photosynthetic microorganisms of hot spring travertines this review describes the known cyanobacterium flora of travertine depositing waters 37 c the communities develop either upon epilithon or within endolithon the travertine surface where they may influence the travertine fabric by providing nucleation sites for calcium carbonate mat photosynthesis locally increases the amount of travertine deposited but the importance of photosynthesis in travertine deposition is rarely significant because the main loss of co2 is by atmospheric evasion of the hot co2 rich waters the oscillatoriales are the most important group of cyanobacteria in terms of their biomass but the taxonomy of the order is in a state of chaos molecular methods will ultimately disclose the true affinities of the organisms but at present the use of form taxa based upon morphological characters provides a practical alternative identification of fossilized cyanobacteria is problematic sin

tectonic evolution and copper gold metallogenesis of the papua new guinea and solomon islands region papua new guinea and the solomon islands are in one of the most prospective regions for intrusion related mineral deposits however because of the tectonic complexity of the region and the lack of comprehensive regional geological datasets the link between mineralization and the regional scale geodynamic framework has not been understood here we present a new model for the metallogenesis of the region based on a synthesis of recent studies on the petrogenesis of magmatic arcs and the history of subduction zones throughout the region combined with the spatio temporal distribution of intrusion related mineral deposits and six new deposit ages convergence at the pacific australia plate boundary was accommodated from at least 45 ma by subduction at the melanesian trench with related melanesian arc magmatism the arrival of the ontong java plateau at the trench at ca 26 ma resulted in cessation of subduction immediately followed by formation of cu au porphyry epithermal deposits at 24 20 ma throughout the melanesian arc late oligocene to early miocene tectonic reorganization led to initiation of subduction at the pocklington trough and onset of magmatism in the maramuni arc the arrival of the australian continent at the pocklington trough by 12 ma resulted in continental collision and ore deposit formation from 12 to 6 ma this is represented by cu au porphyry deposits in the new guinea orogen and epithermal au systems in the papuan peninsula from 6 ma crustal delamination in papua new guinea related to the prior pocklington trough subduction resulted in adiabatic mantle melting with emplacement of diverse cu and au porphyry and epithermal deposits within the papuan fold and thrust belt and papuan peninsula from 6 ma to the present day subduction at the new britain and san cristobal trenches from ca 10 ma resulted in an escalation in tectonic complexity and the onset of microplate tectonics in eastern papua new guinea and the solomon islands this is reflected in the formation of diverse and discrete geodynamic settings for mineralization within the recent to modern arc setting primarily related to upper plate shortening and extension and the spatial relationship to structures within the subducting slab

valanginian weissert oceanic anoxic event biotic changes in nannofossils and radiolarians associated with the valanginian 1 3 c anomaly are documented at ocean drilling program hole 1149b in the pacific ocean they are coeval and similar to those previously documented in the tethys suggesting a global perturbation of marine ecosystems a marked increase in abundance of diazomatolithus absence of nannoconids and a pantanellium peak characterize the valanginian 1 3 c excursion such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess co 2 the occurrence of organic c rich black shales in the southern alps and in the pacific in the interval corresponding to the 1 3 c excursion suggests a valanginian oceanic anoxic event oae volcanism of the parana etendeka large igneous province ca 132 ma was presumably responsible for an increase of co 2 triggering a climate change and accelerated hydrological cycling possibly causing an indirect fertilization of the oceans widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the gondwana breakup and simultaneous tectonic events in three separate oceans there is no paleontological or 1 8 o evidence of warming during the valanginian oae on the contrary both nannofossils and oxygen isotopes record a cooling event at the climax of the 1 3 c excursion weathering of basalts and burial of organic c rich black shales were presumably responsible for co 2 drawdown and establishment of reversed greenhouse conditions

an integrated model of magma chamber conduit and column for the analysis of sustained explosive eruptions abstract explosive volcanic eruptions comprise a complex series of processes involving withdrawal from the magma chamber magma ascent along the conduit and eruption column dynamics numerous studies have modeled the different sub domains of a volcanic system but their interplay has seldom been analyzed to this end we developed c 3 c cubed that stands for chamber conduit and column a new integrated model that describes the dynamics of an explosive eruption as a series of steady state regimes and as a function of geometry and initial conditions of the magma reservoir we used global sensitivity analysis to quantify the role of the relevant model parameters and describe the interplay between the different volcanic sub domains in particular we analyzed the evolution of a sustained explosive eruption in order to identify the conditions for buoyant super buoyant and collapsing columns input data were based on field reconstructions of quaternary explosive eruptions in the vulsini volcanic district roman province central italy model results show that 1 the column regime although affected by complex interactions among several factors mostly depends on the conduit radius the volatile content i e supersaturation concentration at the top of the chamber and length of the conduit in decreasing level of importance 2 the amount of mass erupted is independent of the conduit radius and depends mostly on volatile supersaturation the radius of the magma chamber the length of the conduit and the overpressure at the conduit inlet 3 the mass flow rate column height and duration of the eruption are largely controlled by the conduit radius 4 the flow pressure and density at the conduit exit are mostly controlled by the conduit inlet overpressure at the onset of the eruption and by the length of the conduit at the end of the eruption 5 the exit velocity from the conduit is mostly controlled by the volatile content the length of the conduit and the inlet overpressure in this model framework and with specific reference to selected plinian events of the vulsini volcanic district simulation results show that column collapse is not achieved for reasonable eruption durations order of hours and conduit widths tens of meters this is consistent with field reconstructions suggesting that column collapse did not likely occur and that pyroclastic flows were therefore generated by independent mechanisms from ring fissures and or multiple vents concomitant to caldera collapse

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

the dynamics of travertine dams we present a simple abstract model for travertine dam formation the simulation uses a depth averaged hydrodynamic code coupled with an empirical precipitation model where surface normal growth rate is proportional to local flow rate the dynamics of the resulting formation coarsening and migration progradation of crests is demonstrated and compared with field observations the local self enhancement of crests due to increasing flow rate in combination with lateral inhibition due to upstream drowning implies a classical pattern formation system with a characteristic dam size however this wavelength is not stable but increasing the model also reproduces crest lobes step bunching and other processes that contribute to the complex dynamics of travertine systems

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

sedimentology of hot spring systems hot springs and geysers hold a special fascination for many people to the casual visitor and tourist they provide a powerful visual display of nature at work if their temperature is tolerable taking the waters can provide relaxation comfort and alleged health benefits to the scientist however terrestrial hydrothermal systems are of major importance in many disciplines they serve as models for understanding the processes in the shallowest part of the geothermal systems that produce epithermal mineral deposits they are commonly the surface manifestation of large subsurface geothermal systems that may be tapped for geothermal energy their fascinating ecosystems are dominated by diverse arrays of microorganisms many of which thrive in waters of extremely high temperatures and compositions that are toxic to all other organisms although the life of a geothermal system may be geologically brief typically lasting only a few hundred to a few hundred thousand years many hot springs leave a tangible record of former activity in the deposits that were precipitated in and around their vents these hot spring deposits which are composed mainly of calcium carbonate travertine and silica siliceous sinter are the topic of this special issue hot spring deposits have been studied seriously for more than a century the pioneer of their detailed study was walter harvey weed who in the 1880s was one of the first to examine the deposits of siliceous sinter and travertine at yellowstone national park in wyoming u s a more than a century ago weed 1889 a 1889 b 1889 c recognized that the abundant microorganisms that inhabit spring environments may play a role in the formation of travertine and sinter the subsurface geothermal systems that feed hot springs were widely studied with a view to understanding and predicting epithermal mineralization interest in surface hot spring deposits however

geoinformatics in morphological study of river paglia tiber river basin central italy this work reports the results of a geomorphological study on the river paglia tiber basin central italy to analyse the historical evolution of the riverbed floodplain system in its lower valley reaches upstream the confluence of river tiber a morphological sedimentological approach has been used starting with an historical analysis and a survey of the forms and sediments in the riverbed alluvial plain system in order to reconstruct the current evolutionary trend and to identify the causes and processes leading to changes in natural trends this approach is not in contrast to the hydrologic hydraulic one normally applied in engineering fields but it is integrated with it in a complementary and parallel manner in order to achieve the complete knowledge of the river system result of an investigation multidisciplinary aimed to define its physical state historical data cartographic documents digital terrain models dtm topographic surveys aerial photographs etc indicate clear cut narrowing and deepening of the active channel manifested after the second world war and due to the considerable changes which affected the entire fluvial system from the recovery of land for agriculture near the river to sediments taken from its bed over the past few decades the result is a state of great disequilibrium which is shown in the passage from a braided morphology observed in the 1950s to a single channel with low sinuosity wandering type this type of morphology is certainly more unstable in fact the narrowing and deepening of fluvial sections provide a better hydraulic efficiency for the upstream so the peak discharge does not overflow such peak discharge arrives downstream next to the confluence with the tiber river not laminated causing serious flooding effects an increased vulnerability is observed in the last reach in the areas pertaining to the river where most of the industrial economic activities are concentrated and where transportation infrastructures of nationwide importance italy s most important motorway the a1 and the rome florence milan high speed rail links are located the evolution of the paglia which is not substantially different from that of many streams in italy and in general throughout europe is affected by severe anthropic constraints and intense exploitation of resources which have produced a state of disequilibrium approaching irreversibility in an already vulnerable system finally some suggestions for the correct management of the river system are pointed out with the aim of mitigating the flood risk in the lower paglia valley

on the anatomy of magma chamber and caldera collapse the example of trachy phonolitic explosive eruptions of the roman province central italy abstract textural and compositional features of pyroclastic products erupted during caldera forming events often reveal the tapping of different portions of variably zoned magma chambers due to changing geometries of the conduit vent systems here we report on ultrapotassic trachytic phonolitic explosive eruptions of the roman province central italy which show remarkable changes of textural features and glass compositions in the juvenile material even if the bulk chemical composition is essentially constant in each example the lower eruption sequence contains whitish crystal poor leucite free highly vesicular pumice emplaced by early plinian fallout and or pyroclastic currents upsection the eruption sequence contains black low porphyritic sanidine leucite bearing moderately vesicular scoria or spatter emplaced by major pyroclastic flows red tuff with black scoria and associated co ignimbrite coarse lithic rich breccias this suggests a shift from a central feeder conduit tapping the central part of the magma chamber to a ring fracture vent system tapping the peripheral portions of the magma chamber during caldera collapse key features of these evacuating magma chambers are the thermal and volatile concentration xvol gradients that produce the observed textural and compositional spectrum of trachy phonolitic rock types in particular the degrees of freedom during the crystallization of these ultrapotassic magmas are increased by the variation of the leucite stability field at different ph2o conditions both leucite free and leucite bearing differentiated ultrapotassic rock types can be produced in the course of individual eruptions as a result of pre eruptive conditions in the feeder magma with no need to invoke different differentiation suites related to mantle source heterogeneities of parental magmas

long term risk in a recently active volcanic system evaluation of doses and indoor radiological risk in the quaternary vulsini volcanic district central italy abstract volcanic rocks in the vulsini volcanic district central italy contain high concentrations of 238u 232th and 40k due to subduction related metasomatic enrichment of incompatible elements in the mantle source coupled with magma differentiation within the upper crust due to their favorable mechanical properties they have been extensively used for construction since the etruscan age in the old buildings of the bolsena village one of the most populated ancient village in the area the major source of indoor radioactivity is 222rn a radioactive noble gas descendant of 238u direct 222rn indoor measurements have detected extremely high values in the old center due to the combined effect of building materials radon fluxes from the volcanic basement and low air exchange rates in these cases the evaluated risk of developing lung cancer within a 75 year lifetime reaches up to 40 for ever smokers simulations of standard rooms built with different tuffs and lavas collected from the vulsini volcanic district have also provided estimations of the effective doses and lifetime risk for radiogenic cancer other than by the method adopted for calculation the total evaluated risk for each volcanic rock depends on different parameters such as radionuclide content radon emanation power occupancy factor and air exchange rate occupancy factor and air exchange rate appear as the only controlling parameters able to mitigate the indoor radiological risk

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

comparative study of the lower and mid cretaceous sequences on different maghrebian shelves and basins their place in the evolution of the north african atlantic and neotethysian margins abstract the lower and mid cretaceous sequences known from morocco coastal essaouira agadir safi basin and eastern rif foreland in western algeria da a mountains and finally in southern tunisia chott range and saharian shelf are presented from a biostratigraphic and sedimentologic viewpoint this work shows for the period considered common features in the geodynamic evolution of the different regions such as 1 generalization of the carbonate facies in the early cretaceous berrisian and at the end of the mid cretaceous cenomanian turonian times 2 delineation of important discontinuities in the valanginian and bedoulian times this evolution gives evidence of an undeniable influence of eustatism in this northern part of africa nevertheless detailed differences allow us to distinguish 3 an atlantic type evolution characterized by discontinuities with gaps safi or sudden variations of thickness essaouira agadir at the berriasian valanginian boundary related to the neocimmerian rifting and block faulting phase later on this evolution is underlined by a progressive acceleration of subsidence at the aptian albian boundary due to the removal of the mid oceanic doming 4 a neotethysian type evolution eastern rif foreland western algeria and southern tunisia where local tectonic movements have probably generated the rapid growth of the external marly bedoulian basins and the spreading of the wealdian type valanginian to barremian and utrillas albian terrigenous depositional systems the latest event is linked to the austrian tectonic phase responsible of variable gaps towards the aptian to albian transition

a high resolution tephrochronological record of mis 14 12 in the southern apennines acerno basin italy abstract lithological mineralogical and glass chemical analyses on juvenile fragments extracted from 20 tephra layers embedded within the lacustrine sediments of the acerno basin southern apennines italy were carried out together with four sanidine 40 ar 39 ar age determinations the measured ages span the interval between 561 and 493 ka middle pleistocene eruptive activity at roman province volcanoes was identified as the main possible source of the investigated tephra layers some of them were correlated with precise terrestrial counterparts corresponding to large explosive events of the sabatini e g tufo giallo della via tiberina and alban hills volcanic districts e g tufo pisolitico di trigoria the integration of tephrochronology and pollen analyses allowed the acerno lacustrine sedimentation to be constrained between mis 14 and 12 which overlaps with several well studied lacustrine successions of the southern apennines the correlation with other tephrostratigraphic records from intramontane basins in central southern apennines testifies to the wide dispersal of at least three tephra layers that serve as marker layers thus improving the resolution of the middle pleistocene italian tephrostratotype

the eruptive history and volcanic hazards of savo solomon islands savo island is the 6 km diameter emergent summit of an andesitic dacitic stratovolcano rising from the iron bottom sound 35 km nw of honiara solomon islands savo has erupted at least three times within recorded history and the 3 000 inhabitants maintain extensive oral traditions of past events through description and interpretation of the volcaniclastic sequences on the island in conjunction with historical accounts and oral traditions we reconstruct the eruptive processes on savo block and ash flow baf deposits are volumetrically dominant on the island within three main depositional environments near vent sequences thick medial channel sequences and distal fan sequences the deposits comprise universally non vesicular and highly porphyritic 40 70 phenocrysts high silica andesite and dacite clasts these appear to have been derived from collapsing lava domes during an 1560 1570 a d eruption however eyewitness descriptions and crater morphology suggest that similar deposits formed from dome explosions or collapses of eruption columns during later eruptions 1830 1840 a d the high sodium magmas ca 5 7 wt na2o apparently crystallised and strongly degassed prior to eruption shallow explosions were possibly caused by entrapment of magmatic gases beneath a dome or conduit plug of highly crystalline near solid magma repeated sealing of the vent may have been due to inward collapse of the highly altered rocks of the surrounding hydrothermal system these rocks probably were saturated due to contemporaneous high intensity rainfall events bafs were hot enough to char vegetation and attain aligned clast trm thermal remnant magnetism up to 3 km from the vent many being accompanied by ash cloud surges changes with distance in the baf deposits appear mostly dependent on flow confinement and are limited to an overall decrease in thickness and maximum clast size and an increased definition of weak planar fabrics in distal fan sequences there is strong evidence for syn and post eruptive redeposition of primary deposits since the savo population is concentrated on coastal volcaniclastic fans we consider the greatest volcanic risk to life is from bafs associated ash cloud surges and lahars hence the main channels and fans are designated as the highest of three relative hazard zones on a simple map prepared to aid local education and planning initiatives on savo

shallowing upward sequences in purbeckian peritidal carbonates lowermost cretaceous swiss and french jura mountains purbeckian carbonates in the swiss and french jura goldberg formation lower berriasian comprise shallow subtidal intertidal supratidal low energy high energy marine brackish freshwater and hypersaline facies these facies are arranged in small 0 2 1 5 m thick sequences which display a dominant shallowing upward component and which form the fundamental units of the highly structured purbeckian sedimentary record six types of small scale sequences can be recognized a intertidal to supratidal overprinting of shallow lagoonal facies b algal marsh sequence with frequent dolomitization c sabkha sequence often associated with collapse breccia d tidal flat sequence with desiccation features e lacustrine sequence f terrestrial overprinting of subtidal or intertidal facies episodic event deposits such as tempestites are superimposed thin transgressive beds which rework elements of the underlying facies are frequently found at the base of the sequences green marls and black pebbles are common at the top and indicate long subaerial exposure the sequences are often incomplete as subtidal facies may be absent or their upper part can be eroded lateral facies changes are common which is due to the very shallow and partly emergent purbeckian platform where various depositional environments were juxtaposed however many sequence boundaries are well developed and can be correlated over large parts of the study area the purbeckian shallowing upward sequences were generated by climatically controlled sea level changes autocyclic processes occurred locally but were overprinted by drops of sea level affecting the entire platform the small scale sequences are most probably related to the 20 000 year cycle of the precession of the equinoxes larger sequences with usually well developed emersion surfaces are attributed to the 100 000 and 400 000 year eccentricity cycles of the earth s orbit identification and correlation of sequence boundaries makes it possible to set up a framework of isochronous surfaces which often cut across facies boundaries and thus to interpret in detail the palaeogeographic sedimentological and diagenetic evolution of the purbeckian peritidal carbonate environments

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

an unusual modern silica carbonate sinter from pavlova spring ngatamariki new zealand a silica carbonate deposit is forming from the dilute alkali chloride waters of pavlova spring a small thermal pool and outflow channel 85 to 10 times lower accumulation rates than typical siliceous sinters in the tvz and deposition of both silica and calcite is controlled by microchemical conditions and local temperature gradients rather than by bulk spring water chemistry

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

genesis of large siliceous stromatolites at frying pan lake waimangu geothermal field north island new zealand lilypad stromatolites up to 3 m long and 1ae5 m wide were found to be actively growing in the shallow marginal waters of frying pan lake and its outflow channel these stromatolites composed of phormidium 90 fischerella and a variety of other microbes develop through a series of distinct growth stages dark green microbial mats cover the floor of the outflow channel and give rise to columns of various sizes and shapes in the shallower marginal waters once the columns reach the water level the mats spread laterally to form a lilypad stromatolite the lilypads are characterized by a raised dark green rim 4 5 mm high that encircles a flat interior covered with a distinctive orange red mat the microbes forming the columns and lilypad plate are being actively silicified the stromatolites are formed of i flat lying phormidium filaments p laminae ii upright filaments of phormidium that are commonly associated with fischerella u laminae and iii mucus diatoms and pyrite framboids m laminae p laminae dominate most of the columns with tripartite cycles of p u to m laminae being found mostly in the upper parts of the stromatolites the transition from the p to u laminae is marked by a change in the growth pattern of the phormidium and branching of fischerella which was probably triggered by a change in environmental conditions in the frying pan lake outflow channel this change may be related to fluctuations in water level and flow rates that are caused by periods of heavy rain seasonal changes long term variations in rainfall and or the unique 40 day hydrological cycle that exists between frying pan lake and inferno crater which is a nearby hydrothermal crater lake

caldera structure amount of collapse and erupted volumes the case of bolsena caldera italy calderas are common on volcanoes but their structure is seldom visible the 19 km wide bolsena caldera italy formed between 0 6 and 0 2 ma the largely preserved structural rim and subsurface data make bolsena ideal to investigate caldera structure in relation to the subsidence and erupted volume in this paper we use remote sensing field analysis and available subsurface data at the surface the caldera passes from a downsag south rim to a narrow and densely faulted area north rim with outer normal and inner reverse faults the caldera structure on the widely faulted east rim appears to be scale dependent with a staircase like fault zone larger scale horst and graben like structures intermediate scale and domino like structures smaller scale subsurface data indicate asymmetric collapse with a northward increase in subsidence ranging from diffuse to the south to focused to the north deformation at the surface the collapse rate constant between ca 490 and 175 ka was more than magma output between ca 330 and 130 ka highlighting significant 200 m and prolonged 200 ka posteruptive subsidence as the nearby latera caldera west rim of bolsena was mostly active between ca 265 and 160 ka much of the subsidence at bolsena may be related to this activity suggesting a common magmatic reservoir the subsidence related structural variations along the caldera rim and the significant posteruptive subsidence found at bolsena have not been found in other calderas

mixed biogenic and hydrothermal quartz in permian lacustrine shale of santanghu basin nw china implications for penecontemporaneous transformation of silica minerals the cycling of various isomorphs of authigenic silica minerals is a complex and long term process a special type of composite quartz qc grains in tuffaceous shale of permian lucaogou formation in the sediment starved volcanically and hydrothermally active intracontinental lacustrine santanghu rift basin nw china is studied in detail to demonstrate such processes samples from one well in the central basin were subject to petrographic elemental chemical and fluid inclusion analyses about 200 qc bearing laminae are 0 1 2 mm and mainly 1 mm thick and intercalated within tuffaceous shale laminae the qc grains occur as framework grains and are dispersed in igneous feldspar dominated matrix suggesting episodic accumulation the qc grains are bedding parallel uniform in size 100 s m elongate and radial in crystal pattern suggesting a biogenic origin qc grains are composed of a core of anhedral microcrystalline quartz and an outer part of subhedral mega quartz grains whose edges are composed of small euhedral quartz crystals indicating multiple episodic processes of recrystallization and overgrowth abundance of al and ti in quartz crystals and estimated temperature from fluid inclusions in qc grains indicate that processes are related to hydrothermal fluids finally the qc grains are interpreted as original silica precipitation in microorganism algae cysts which were reworked by bottom currents and altered by hydrothermal fluids to recrystalize and overgrow during penecontemporaneous shallow burial it is postulated that episodic volcanic and hydrothermal activities had changed lake water chemistry temperature and nutrient supply resulting in variations in microorganic productivities and silica cycling the transformation of authigenic silica from amorphous to well crystallized had occurred in a short time span during shallow burial

tephro chronostratigraphy of the lacustrine interglacial record of pianico italian southern alps identifying the volcanic sources using radiogenic isotopes and trace elements abstract the chronostratigraphic position of the pianico carbonate sequence oroebic alps italy remains controversial notwithstanding that it is one of the best preserved records of an alpine interglacial two distal tephra were discovered in the sequence the lowermost t21d is a rhyolitic tephra dated by k ar at 779 13 ka different from the uppermost phonolitic tephra t32 with an assigned age of 393 12 ka the volcanic source of t32 was recently interpreted as being the brown leucitic tuff of the roccamonfina volcano southern italy new trace element and nd and sr isotopic composition of t32 and of 420 200 ka volcanic products of the roccamonfina clearly indicate that this volcano is not the source of t32 but that it likely originated from the northern roman magmatic province the products of the initial explosive activity of sabatini mts dated ca 780 800 ka isotopically match t32 and are proposed as its source this indicates that the previously inferred age of 400 ka for t32 is erroneous new isotopic and geochemical data of t21d confirm it as being associated with the first pyroclastic eruptions 790 710 ka of the puy de sancy volcano french massif central the early middle pleistocene k ar ages obtained previously for t21d together with the isotopic attribution of volcanic sources to both tephra layers presented here confirm pianico as one of the best interglacial sequences of cromerian age in the western alps

sequence stratigraphy of lower cretaceous barremian albian carbonate platforms of northeastern mexico regional and global correlations abstract the lower cretaceous cupido and coahuila platforms of northeastern mexico form part of the extensive carbonate platform system that surrounded the ancestral gulf of mexico a sequence stratigraphic model for these barremian to albian platforms was constructed from regional correlations of vertical cycle stacking patterns constrained by newly acquired biostratigraphic data and c and sr isotope stratigraphy the cupido shelf lagoon barremian aptian is composed of up to 150 peritidal cycles which stack into high frequency sequences that are correlated across the shelf cupido high frequency sequences build into a lower partial composite sequence cu1 an overlying full composite sequence cu2 and the transgressive base of a third composite sequence cu co3 related to backstepping of the cupido platform the highstand part of cu co3 is recorded in evaporite and carbonate facies of the coahuila platform aptian albian more than 80 meter scale evaporite to carbonate cycles characterize the restricted interior of the coahuila platform and stack into two full composite sequences co4 co5 the coahuila platform was drowned in the latest albian or earliest cenomanian terminating shallow water carbonate sedimentation in the region regional correlations of the depositional sequences in northeast mexico with coeval platforms in texas and the northern gulf coast indicate that the lower two composite sequences of the cupido shelf correlate with the lower part of the sligo hosston platform in texas the transgressive systems tract of the third composite sequence of the cupido la pena is recorded in texas by the upper sligo and pearsall formations the highstand systems tract and the disconformable top of the third composite sequence coahuila platform is likely coeval with the upper glen rose platform in texas the fourth and fifth composite sequences are correlative with the fredericksburg platform and the washita devils river platforms of texas respectively we conservatively correlated our sequence stratigraphic framework with composite global sequences and eustatic curves derived from several other basins given the available time resolution results are variable but sequence boundaries at the top of cu co3 and co5 appear to have clear interbasinal equivalents

the hot spring and geyser sinters of el tatio northern chile abstract the siliceous sinter deposits of el tatio geothermal field in northern chile have been examined petrographically and mineralogically these sinters consist of amorphous silica opal a deposited around hot springs and geysers from nearly neutral silica saturated sodium chloride waters water cooling and evaporation to dryness are the main processes that control the opal a deposition in both subaqueous and subaerial settings in close spatial relation to microbial communities all fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse cyanobacteria green bacteria and diatoms the most important ecological parameter is the temperature gradient which is closely related to the observed depositional settings 1 geyser setting water temperature 70 86 c boiling point at el tatio 4200 m a s l coarse laminated sinter macrostructure with rapid local variations biota comprises non photosynthetic hyperthermophilic bacteria 2 splash areas around geysers water temperature 60 75 c laminated spicule and column macrostructure locally forming cupolas

anomalous alkaline sulphate fluids produced in a magmatic hydrothermal system savo solomon islands abstract in magmatic hydrothermal and associated geothermal systems acidic magmatic derived fluids ph 5 geothermal fluids are typically limited to lateral outflows some distance from the main vent here we describe an unusual hydrothermal system associated with savo volcano a recently eruptive 1830 1840 ad trachyte dominated island arc stratovolcano in the solomon islands hot springs 100 c near to the volcanic crater discharge alkaline waters instead of the more commonly recognised acidic fluids the hydrothermal system of savo dominantly discharges sinter and travertine forming alkaline sulphate ph 7 8 waters at hot springs on its upper flanks in addition to a small number of lower discharge acid sulphate springs ph 2 7 alkaline sulphate fluids are dilute chloride poor 600 mg l and silica rich 250 mg l they have restricted 34sso4 5 4 1 5 and 18oh2o values 4 local non thermal groundwater is 8 acid sulphate springs discharge low chloride geochemical modelling shows that water rock reaction and dilution in the presence of secondary anhydrite pyrite and quartz leads to chloride being diluted to low concentrations whilst maintaining high sulphate and silica concentrations in the fluid strontium oxygen and hydrogen isotopes confirm water rock reaction and mixing with groundwater as primary controls on the composition of the alkaline sulphate springs the highly unusual dilute chemistry of all discharges at savo is a consequence of high regional rainfall i e climatic control and results from open system mixing at depth between hydrothermal and meteoric waters

a model for episodic degassing of an andesitic magma intrusion 1 episodic magmatic degassing has been observed at numerous volcanoes especially those of intermediate composition it can span timescales from years to decades here we propose a physical model for the degassing of a shallow magma intrusion to explain this phenomenon the magma cools by convection which leads to melt crystallization volatile exsolution and magma overpressure when the pressure reaches a critical value wall rocks fracture and the exsolved gas escapes the intrusion then returns to the initial lithostatic pressure and a new cooling crystallization degassing cycle occurs a series of such cycles leads to episodic degassing the trend and timescale of the degassing process are mainly governed by magma cooling two degassing regimes are exhibited an early phase with a high frequency of gas pulses and a later phase with a lower gas pulse frequency the transition between these two regimes is caused by the viscosity increase when the magma crystallinity exceeds the crystal percolation threshold we find that the time to this transition is dependent on magma volume to a first approximation where observations are available from sustained geochemical surveillance the model provides constraints on key aspects of the subsurface magmatic system with estimation of the volume of an intrusion and tensile strength of the surrounding rocks it therefore represents a relevant tool for volcanic surveillance and hazard assessment

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

40ar 39ar single crystal dates from pyroclastic deposits provide a detailed record of the 590 240 ka eruptive period at the vulsini volcanic district central italy abstract we analyze the age distribution provided by 113 sanidine crystals separated from six samples of pyroclastic products of the bolsena orvieto phase of activity at the vulsini volcanic district which were dated via the 40ar 39ar single crystal total fusion method in a previous study moreover we investigate the compositional and depositional features of the dated products both at the outcrop scale and at the optical microscope aimed at discriminating the juvenile vs antecrystic vs xenocrystic origin of the dated crystals results of this study provide insights on the magmatic process preceding the eruptions as well as on the eruptive mechanisms of the primary deposits the data also provide a geochronologic context to the history of eruptive activity of the vulsini volcanic district from 590 to 250 ka with greater detail than previously outlined by direct dating of several primary units indeed most of the six samples analyzed in the present work yielded 19 distinct crystal population ages 10 of which match those of previously dated eruptive units and the other 9 possibly corresponding to primary deposits so far undated

eustatic control on early dolomitization of cyclic peritidal carbonates evidence from the early ordovician upper knox group appalachians the early ordovician upper knox group is characterized by stacked meter scale peritidal cycles that repeat at high frequencies 10 4 to 10 5 yr stacking patterns stratigraphic trends in lithofacies and cycle thickness of meter scale cycles define five depositional sequences that in conjunction with fischer plots delineate five long term relative sea level fluctuations during upper knox deposition intrabasinal and interbasinal correlation of upper knox fischer plots suggests that the third order sea level events were eustatic meter scale peritidal cycles likely formed in response to high frequency fourth and fifth order eustatic sea level fluctuations superimposed on these third order sea level events upper knox cyclic carbonates are extensively dolomitized as much as 85 of all dolomite is stratiform and consists of early dolomite exhibiting minor to extensive modification by burial dolomite synsedimentary dolomitization likely occurred in modified sea water during tidal flat progradation governed by high frequency sea level events this is suggested by the common association of dolomite with mud cracked laminites and silicified evaporite nodules the systematic decrease in dolomite abundance below laminite cycle caps and the presence of dolomite clasts in regoliths veneering high frequency cycle tops or in transgressive limestones of the overlying cycle dolomite distribution within depositional sequences shows a strong relationship to third and fourth order eustatic sea level events indicating that long term eustasy also strongly controlled early dolomitization of upper knox carbonates mass balance calculations show that the proposed sabkha model of dolomitization in concert with composite eustasy could generate stratiform dolomite of considerable vertical and lateral extent in peritidal cyclic carbonates this reflects the duration of progradation and supratidal exposure 10 4 to 10 5 yr available for dolomitization to proceed and the broad zone of active dolomitization that would develop during continued progradation throughout each cycle period

anatomy of siliceous hot springs examples from yellowstone national park wyoming usa abstract numerous siliceous hot spring systems in the norris and lower geyser basins of yellowstone national park wyoming provide insights into spring geometries depositional facies and lithofacies associated with modern hot springs analyses of active cistern spring octopus spring deerbone spring and spindle geyser and inactive pork chop geyser siliceous hot springs have facilitated the construction of a facies model for siliceous hot spring deposits at yellowstone yellowstone s siliceous springs tend to group into four broad morphological categories siliceous spires and cones domal mounds terraced mounds and ponds siliceous spires cones are subconical accumulations up to 5 7 m high and about 2 m in diameter and are common deposits in yellowstone lake domal mounds are characterized by siliceous precipitates with a broad lens or shield geometry 2 3 m in vertical relief discharge channels and an areal accumulation of approximately 150 m2 in contrast terraced mounds have a stair step morphology a substantial pool 8 10 m in diameter shrubby precipitates and occupy areas of 2000 m2 siliceous ponds are variable in size have little outflow and exhibit low amounts of silica precipitation of these morphological varieties domal mounds and terraced mounds are thought to have the best long term preservation potential the four spring morphotypes are composed of up to eight cumulative hot spring depositional facies 1 vent 95 c 2 proximal vent precipitation of siliceous sinter is the result of abiotic and biotic processes abiotic precipitational processes are dominant in the vent area whereas biotic influences on the precipitate fabric become progressively more important downflow

geothermal mineralization i the mechanism of formation of the beowawe nevada siliceous sinter deposit the siliceous sinter deposit at beowawe nev has a volume of 7 71 x 10 sup 7 m sup 3 and contains 1 28 x 10 sup 11 kg silica this silica precipitated from geothermal solutions that welled up along the malpais fault a graben bounding fault sinter formation involved three steps 1 geothermal solutions saturated with quartz in the reservoir moved to the surface where they cooled and became supersaturated with amorphous silica 2 amorphous silica particles nucleated heterogeneously to produce a colloidal suspension 3 the amorphous silica particles agglomerated and were cemented together by amorphous silica precipitating in the embayments between the particles at least 5 58 x 10 sup 14 kg of geothermal solution must have been produced over time to account for the mass of silica in the beowawe deposit this fluid would have carried at least 4 95 x 10 sup 17 kj of heat to the surface 21 references 6 figures 1 table

diagenetic transformations opal a to quartz of low and mid temperature microbial textures in siliceous hot spring deposits taupo volcanic zone new zealand silica sinter is a subaerial hot spring deposit formed upon cooling 100 c of discharging alkali chloride waters silica deposition traps and fossilizes living microbes in low temperature 35 c to mid temperature 35 59 c apron terrace outflow channels and pools which record distinctive macrotextures and microtextures along a thermal gradient sinters from four geothermal fields orakei korako northern waiotapu te kopia and umukuri within the taupo volcanic zone new zealand were sampled from two common microbe rich microfacies low temperature palisade mid temperature bubble mat through a range of ages modern to 40 000 years bp we observed morphologic changes in microbial silicification and stepwise transitions in silica phase mineralogy throughout diagenesis opal a to quartz x ray powder diffractometry analysis of taupo volcanic zone sinter samples revealed that mode of microbial fossilization is controlled by silica phase mineralogy which also determines the preservation potent

aptian albian sea level history from guyots in the western pacific relative sea level fluctuations are an important control on patterns of sedimentation on continental margins and provide a valuable tool for regional correlations one of the main objectives of combined ocean drilling program legs 143 and 144 was drilling the thick carbonate caps of a suite of seamounts called guyots scattered over the northwestern pacific the array of drowned cretaceous banks includes four carbonate banks of aptian albian age these particular carbonate banks display emergent surfaces if regional sea level falls faster than the rate of guyot subsidence or intervals of condensed parasequences and well cemented peritidal crypto algal flats if the rate of sea level fall is slightly less than guyot subsidence rapid rises of sea level following these sequence boundaries are recorded as drowning of the emergent horizons or as pronounced deepening of facies the cored lithologies and downhole geophysical and geochemical logs were used to identify depositional sequences and surfaces of exceptional shallowing or deepening a combination of biostratigraphic datums carbon and strontium isotope curves relative magnitude of surfaces of emergence relative thicknesses of depositional sequences sea level events and counts of upward shallowing cycles or parasequences were used to correlate sequences among the four sites after compensating for thermal subsidence rates at each guyot an identical pattern of major aptian albian eustatic sea level events is evident throughout this large portion of the pacific ocean there are approximately 12 aptian and 12 albian significant sequence boundaries of which a third were associated with major episodes of emergence when these events are compared with aptian albian relative sea level changes observed in european shelf successions the major sequence boundaries and transgressive surges can be easily correlated and it appears that both regions also display the same number of minor events therefore we can apply the relative timing of these events from the thermal subsidence rates and parasequence counts of the pacific banks to construct an improved scaling of the associated ammonite zones and biostratigraphic datums in the aptian albian interval an electronic supplement of this material may be obtained on adiskette or via anonymous ftp from kosmos agu org loginto agu s ftp account using anonymous as the username andguest as the password go to the right directory by typing apend diskette may be ordered from american geophysical union 2000florida ave n w washington d c 20009 15 00 payment mustaccompany order

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

geology and volcanology of san venanzo volcanic field umbria central italy the purpose of this paper is to integrate or even modify where necessary the geovolcanological setting outlined by other authors on the history of the small volcanic field of san venanzo umbria central italy to attain this goal new accurate field investigations were carried out in that area coupled with detailed stratigraphic studies and laboratory analyses to support field evidence with experimental results the first objective was to stress the importance of a groundwater reservoir whose interaction with magma at various degrees was responsible not only for the explosive character of volcanism in that area but also for the complex morphology of the volcanic deposits that are widely scattered on the underlying sedimentary basement another objective was to clarify the role played by tectonic activity in enhancing the fast and discontinuous ascent of batches of magma from the mantle to the surface through two different sets of faults opened by tectonic unrest into the crust that were also responsible for the morphology and spatial distribution of volcanic centres this was considered to be very important in consideration of the still active stress field of the region finally special attention was focused on the presence of a palaeosol between two eruptive sequences as it most likely denoted a split in the volcanic activity of this site into two separate phases this observation leads to the conclusion that in spite of its eruptive characteristics the small volcano of san venanzo is not monogenic for all of these topics a number of conclusions have been drawn and they are reported with more data in the following sections of this paper

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

evidence for sub lacustrine volcanic activity in lake bolsena central italy revealed by high resolution seismic data sets abstract the bolsena caldera that formed between 0 6 and 0 2 ma has a well preserved structural rim which makes it an ideal site to study the tectonic and volcanic evolution of calderas however the main area is covered by a 150 m deep lake which makes it rather difficult to investigate the subsurface structure directly to overcome this problem new high resolution hydro acoustic surveys using a multichannel reflection seismic system and a sediment echo sounder system were conducted in september 2012 as space was limited we used a rowing boat towed by a rubber boat to handle a 36 m long and 24 channel streamer to receive seismic reflections produced using a mini gi gun 0 25 l the subsurface structure of lake bolsena was imaged up to a sediment depth of 190 m which is estimated to have filled over a period of 333 kyrs however massive pyroclastic flow deposits found in the deeper parts of the basin indicate an initial infill of volcanic deposits from two adjacent younger calderas the latera w and montefiascone se calderas our data suggest that the caldera has a long history of active volcanism because the lacustrine sediments show post sedimentary influences of geothermal fluids we mapped several mound structures at various stratigraphic depths two volcanic structures outcrop at the modern lake surface implying recent activity one of these structures is hardly covered by sediments and has a crater like feature in its summit the other structure shows a pockmark like depression on top another observable feature is a partially sediment filled crater located in the western part of the lake which further implies the existence of a magma chamber located beneath the bolsena caldera since the late pleistocene and holocene the sedimentation was mainly hemipelagic evidenced by a sediment drape of up to 10 m thick sediment drape on the uppermost sediments beneath the drape we found evidence for a distal tephra layer likely related to an explosive eruption from the campanian volcanic province occurring as the neapolitan yellow tuff our new geophysical data set is a valuable record with a potential to constrain the sedimentary and volcanic evolution of the vulsini volcanic district in areas that have not been assessed previously due to logistical challenges of conducting surveys in water filled settings

hot spring and geyser sinters the integrated product of precipitation replacement and deposition complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world including those located in the taupo volcanic zone on the north island of new zealand those sinters are formed of opal a that replaced microbes opal a precipitated as cement accessory minerals e g kaolinite jarosite calcite biological detritus e g leaves wood pollen grains and lithic detritus the opal a is compositionally variable because of the amount of water oh and h2o and in some cases accessory elements e g au ag bound into its structure the composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement precipitation and deposition the microbes that inhabit these systems are of critical importance because they are commonly replaced by and or encrusted with opal a in many settings copious amounts of opal a are precipitated as cement around the frameworks of silicified filaments the cementation pro

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

reply to the discussion by rose of phelps et al 2014 oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico sedimentology 61 461 496 discussion points raised by rose 2016 concentrate on late albian stratigraphic relationships between formations of the east texas basin and the san marcos arch of the comanche platform in the northern gulf of mexico criticisms of phelps et al 2014 regarding stratigraphic nomenclature palaeogeography and regional lithostratigraphic correlations generally focus on interpretive aspects of the study or do not account for the full scope of published information revisions to the top aptian albian supersequence boundary by rose are incompatible with the relative location of a subaerial unconformity as well as deepening lithofacies trends and retrogradational stratigraphic patterns below the interpreted boundary rose s placement of the top aptian albian supersequence boundary precisely at the albian cenomanian stage boundary also implies approximately 1 4 ma of diachroneity in second order sea level patterns between the northern gulf of mexico and other documented global sedimentary basins this article is protected by copyright all rights reserved

bacterial shrubs crystal shrubs and ray crystal shrubs bacterial vs abiotic precipitation hot water travertine deposits commonly contain shrub like morphologies on the centimeter to meter scale that range from highly irregular forms bacterial shrubs to features that display regular geometric patterns crystal shrubs and ray crystal crusts the bacterial shrubs have been previously recognized as the product of bacterially induced precipitation whereas the ray crystal crusts have been described as due to dominantly abiotic precipitation the bacterial shrubs have a highly irregular morphology similar to woody plants in contrast end member crystal shrubs display distinct crystal habits and regular repeating morphologies i e they commonly have attributes of noncrystallographic as well as crystallographic dendrites there is a complete gradational relationship between the bacterial shrubs and crystal shrubs ray crystal crusts are large fan shaped features composed of subparallel extremely coarse bladed crystals of calcite all three types bacterial shrubs crystal shrubs and ray crystal crusts contain either a dense tangle of bacterial body fossils and or micron sized pores the micropores are bacterial molds the immediately enveloping spar crystals around all three morphologic types are devoid of bacterial body fossils and micropores the bacterial shrubs crystal shrubs and ray crystal crusts are to differing degrees the product of bacterially induced precipitation as well as abiotic mineral precipitation the differences in morphology are due to the relative contribution of bacterially induced precipitation as compared with that of abiotic mineral precipitation bacterially induced precipitates can form in environments too chemically harsh or otherwise inhospitable for other taxa to thrive epiphyton and renalcis commonly formed in occult environments under conditions inhospitable to other taxa consideration of the published descriptions and interpretations concerning epiphyton and renalcis and by analogy the origin of bacterial shrubs have led to the conclusion that epiphyton and renalcis also are bacterially induced precipitates

boron isotopic variations in fumarolic condensates and thermal waters from vulcano island italy implications for evolution of volcanic fluids abstract temporal variation in the isotopic composition of boron has been monitored in fumarolic condensates collected over an extended time period 1970 1996 from la fossa crater volcano island we also report comparative boron isotopic data for representative vulcano lavas and for shallow hydrologic samples seawater wells thermal springs from the north flank of la fossa combined with concurrent chemical and isotopic 18o d data for the fumaroles these results indicate that the fumarolic fluids record mixing relations between three distinct fluid end members 1 a dominantly magmatic fluid em1 2 a mixture of modified seawater with magmatic fluid em2 and 3 an aqueous fluid produced from seawater by extensive wall rock reaction evaporation and boiling af differences between the latter two end members are most clearly accentuated on the basis of the boron isotopic data long term compositional variations for crater fumaroles were dominated by em1 af mixing between 1979 88 with progressive decrease in em1 contribution with time and by em2 af mixing between 1988 96 the exact spatial distribution of these fluid reservoirs remains unclear but all must have been present throughout the monitoring period to account for the observed variations moreover the combined b o h data seem to preclude important contributions from shallow meteoric reservoirs marked short term variations in 11b closely coincide with episodes of local seismicity which presumably triggered reorganization of hydrothermal circulation patterns gradual variations over periods up to 3 4 years are associated with relatively low seismicity during which fluid circulation was likely influenced by effects of mineral precipitation on permeability of the hydrologic system

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

epithermal gold mineralization acupan baguio district philippines geology mineralization alteration and the thermochemical environment of ore deposition a large gold rich adularia sericite style epithermal vein system formed at 0 65 ma at acupan baguio district philippines during a period of high k magmatism low salinity asymp 0 5 wt nacl equiv gassy up to 0 41 m co 2 meteoric fluids with temperatures of up to 300 degrees c or more were focused into a series of steeply dipping interconnected faults and joints in the virac granodiorite balatoc diatreme lucbuban gabbro and zig zag formation prolonged and varied geothermal activity resulted in the formation of a series of composite banded epithermal veins with an average width of 1 m that extend to depths of at least 1 km relative to the present day surface the epithermal event was characteried by periods of hydrothermal brecciation interspersed with more quiescent periods when delicate to coarsely banded vein material was precipitated five distinct mineral assemblages have been defined in the epithermal veins type a characterized by fine grained chalcedony type b fine grained gray quartz type c coarse grained white quartz type d coarse grained calcite and type e coarse grained anhydrite electrum and au ag tellurides have been recognized in type b c and d bands interaction of ascending chloride brines with the wall rocks over the lifetime of the system produced intense symmetrical meterwide halos of altered rock characterized by sericitic silicic and sericite chlorite mineral assemblages that grade out to a weak diffuse widespread propylitically altered zone minor adularia alteration is restricted to the deeper mine levels sulfide oxide silicate carbonate phase relationships in the acupan vein system constrain the mineralizing fluids to values of log f sub o 2 between 28 and 33 log f sub h 2 between 1 5 and 3 7 and log log f sub h 2 s between 0 6 and 1 8 at 300 degrees c abundant quartz k mica pyrite alteration and vein mineralization are consistent with silica saturated reduced weakly acidic to weakly alkaline fluid compositions boiling caused the fluids to evolve to more alkaline conditions leading to the sporadic precipitation of adularia in the veins and altered wall rocks dissolved co 2 concentrations were sufficiently high up to 0 41 m to stabilize calcite at the expense of calc silicate minerals mg super 2 concentrations were low in the mineralizing fluids but increased during dissolution of primary hornblende and biotite in the country rocks resulting in the development of a sericitechlorite alteration assemblage in the deep mine levels h 2 s and h 2 co 3 were the predominant sulfur and carbon bearing species and the low salinity gassy nature of the fluids favored gold and silver transport as bisulfide complexes h 2 te and hte super were the predominant aqueous tellurium species entrainment of minor amounts of magmatic volatiles during type c and d mineralization is responsible for te enrichment in the dominantly meteoric fluids and log f sub te 2 ranged between 7 8 and 8 6 at 300 degrees c during periods of hessite deposition magmatic contributions also account for the co sub 2 super and h 2 s rich nature of the fluids and for magmatic helium isotope signatures

seismic stratigraphy of the mid cretaceous unconformity mcu in the central gulf of mexico basin a widespread high amplitude reflection seen on seismic data throughout the gulf of mexico has been called the mid cretaceous unconformity mcu this reflector seems to be a major stratigraphic boundary in the gulf of mexico basin it is believed to correspond to vail s type 1 unconformity of mid cenomanian age 94 ma which records an eustatic drop in sea level of approximately 60 100 m the study area includes all of the gulf of mexico with the exception of areas of thick and highly deformed salt where following the mcu with any degree of confidence becomes impossible the mcu is easy to follow in multichannel seismic reflection profiles collected in the gulf of mexico by the institute for geophysics of the university of texas at austin in the central deeper part of the gulf reflectors above and below the mcu are parallel in the southern and eastern rims of the gulf along the campeche and florida escarpments reflectors are truncated below the mcu and show onlap relationships above it the mcu

evidence of incremental growth in the vulsinian calderas central italy abstract a comparative work on the vulsini calderas has been carried out fundamentally from volcanological field study drilling and gravity anomalies data on the basis of a detailed stratigraphy four volcanic complexes have been recognized in the vulsini volcanic district from the oldest to the youngest paleo bolsena bolsena montefiascone and latera the latter two complexes having a contemporaneous evolution in their activity each complex gave rise to several little calderas caused by piecemeal collapses due to moderate size explosive eruptions or coherent subsidence of a superficial piston like block nevertheless the extensional volcano tectonic regime affecting this area could have accounted for as much of the total subsidence as the caldera forming eruptions bolsena and latera calderas respectively 16 km and 8 km in average diameter represent the main depressions of the vulsini district and their topographic features are still well preserved several collapses forming the main poligenetic calderas of bolsena and latera are masked at present by the bolsena lake the younger volcanic covering the lacustrine deposits and erosion in a minor amount only the little montefiascone and vepe calderas which represent the youngest collapses of the vulsini area have not been masked bolsena caldera could be considered a depression caused mostly by a subsidence hinged to the southwest by down sagging and by collapses which occurred after the most important explosive eruptions of the paleo bolsena bolsena and montefiascone volcanic complexes meanwhile latera caldera is mostly due to a piecemeal collapse linked to several moderate size ignimbrite units which were emplaced throughout the explosive activity of the latera complex therefore the vulsinian calderas did not form by catastrophic eruptions because several and frequent moderate size eruptions downsagging and tectonic hinged subsidence concur indicating an incremental growth

marine carbon burial flux and the carbon isotope record of late cretaceous coniacian santonian oceanic anoxic event iii abstract episodes of widespread distribution of organic rich marine facies within relatively narrow stratigraphic intervals have been interpreted as oceanic anoxic events oaes there are a number of such intervals in the upper cretaceous some of which also exhibit significant positive excursions in carbon isotope records as a result a general model of the relationship between enhanced organic carbon burial and positive c isotope shifts has emerged carbon isotope stratigraphy has therefore developed the dual utility of a chronostratigraphic tool and a means to help identify and define intervals of exceptional organic matter burial and preservation however variations in regional carbon isotope records of globally documented events suggest that the relationship between organic carbon burial flux and magnitude of carbon isotope excursion may not be entirely straightforward for example strata of coniacian santonian age have long been recognized for enhanced organic content in many areas but the designation of oceanic anoxic event iii for this interval has been rather equivocal in the literature mostly due to the weak positive 13 c excursion 0 5 yet in some areas organic carbon accumulation rates for coniacian santonian strata are roughly double that of the older oae ii which is marked by a 2 4 shift in 13 c interestingly the burial flux of carbonate which leads to depletion rather than enrichment of the c isotope signal is also significantly elevated during coniacian santonian time in this study the role of variations in organic carbon and carbonate accumulation rates on carbon isotopic expression are explored through application of data on the composition accumulation rate and areal distribution of end member facies types to the development of a global carbon isotopic mass balance model the results are used to explore the hypothesis that net organic carbon burial during oae iii was not accurately represented in the carbon isotopic record these results have important implications for interpretation of c isotope records related to past perturbations of the global carbon cycle

a case of no wind plinian fallout at pululagua caldera ecuador implications for models of clast dispersal the caldera of pululagua is an eruptive centre of the northern volcanic zone of the south american volcanic arc located about 15 km north of quito ecuador activity leading to formation of the caldera occurred about 2450 b p as a series of volcanic episodes during which an estimated 5 6 km3 dre of hornblende bearing dacitic magma was erupted a basal pumice fall deposit covers more than 2 2x104 km2 with a volume of about 1 1 km3 and represents the principal and best preserved plinian layer circular patterns of isopachs and pumice lithic and md isopleths of the basal fallout bf around the caldera indicate emplacement in wind free conditions absence of wind is confirmed by an ubiquitous normally graded thin ash bed at the top of the lapilli layer which originated from slow settling of fines after cessation of the plinian column co plinian ash the unusual atmospheric conditions during deposition make the bf deposit particularly suitable for the application and evaluation of pyroclast dispersal models application of the carey and sparks 1986 model shows that whereas the 3 2 1 6 and 0 8 cm lithic isopleths predict a model column height of about 36 km the 6 4 cm isopleth yields and estimate of only 21 km the 4 9 and 6 4 cm isopleths yield a column height of 28 km using the model of wilson and walker 1987 the two models give the same mass discharge rate of 2x108 kg s 1 a simple exponential decrease of thickness with distance as proposed by pyle 1989 for plinian falls fits well with the bf exponential decrease of size with distance is followed by clasts less than about 3 cm suggesting in agreement with wilson and walker 1987 that only a small proportion of large clasts reach the top of the column variations with distance in clast distribution patterns imply that in order to obtain column heights by clast dispersal models the distribution should be known from both proximal and distal zones knowledge of only a few isopleths irrespective of their distance from the vent is not sufficient as seemed justified by the method of pyle 1989

interactions between environmental change and shallow water carbonate buildup along the northern tethyan margin and their impact on the early cretaceous carbon isotope record 1 the evolution of the early cretaceous northern tethyan carbonate platform was not only influenced by changes in sea level detrital influx and surface water temperature but also by changes in trophic levels we distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder water heterozoan communities superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy the initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general on the basis of a comparison between the temporal changes in an early cretaceous ammonite calibrated d 13 c record from southeastern france and coeval changes in the platform record we suggest that the history of carbon fractionation along the northern tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir but it was also influenced by the above mentioned changes in the ecology and geometry of the adjacent carbonate platform phases of photozoan carbonate production induced positive trends in the hemipelagic carbonate d 13 c record phases of heterozoan carbonate production pushed the d 13 c system toward more negative values platform drowning episodes implied an initial increase in d 13 c values followed by a longerterm decrease in d 13 c values

plinian fall deposits from vulsini volcanic district central italy stratigraphic investigations of the vulsini volcanic district indicate the existence of five prominent plinian fall deposits deposited over a period of about 0 34 ma the oldest deposit basal pumices crops out mainly in the peripheral areas and is one of the largest plinian events in the vulsini district with a volume of about 9 km3 and a calculated column height exceeding 30 km subcircular patterns of isopachs and isopleths around the bolsena lake indicate emplacement in wind free conditions and suggest a source vent location in the northernmost sector of the present bolsena lake where it is possible that an older central volcanic structure existed the four younger plinian fall deposits are related to bolsena activity the oldest of these named the ponticello and orvieto bagnoregio pumices are mainly distributed on the north eastern sector of the vulsini district their volumes are an order of magnitude lower than that of the basal unit and the estimated column heights do not exceed 20 km the younger ospedaletto pumice deposit has a ne sw dispersal axis whereas the youngest casetta pumice deposit is found only in the north eastern sector of the district their estimated volumes are respectively 1 2 and 0 1 km3 whereas the inferred vent areas appear to be located slightly to the east of the ponticello and orvieto bagnoregio pumice deposit source areas the chronology of the ospedaletto and casetta pumices indicates that the final plinian activity from the bolsena complex is contemporaneous with the latera activity the decreasing volumes from the oldest to the youngest units together with the progressive shifting northeastwards of the source vents may be related to the volcano tectonic subsidence of the bolsena area the source vents for the post basal pumices events are mainly clustered just north of bolsena village where the greatest displacement during subsidence occurred accordingly source vent shifting appears to be related to the progressive opening of normal faults from the inner to the outer margin of the bolsena depression

an exceptionally thick middle pleistocene tephra layer from epirus greece abstract a newly recognized 2 m thick trachytic volcanic ash deposit from northwestern greece is dated at 374 000 7000 yr and correlated with the middle pleistocene volcanic activity of central italy the deposit represents ash fallout from one of the largest volcanic eruptions in europe of the past 400 000 yr and should provide an important stratigraphic marker within the poorly dated middle pleistocene deposits of italy and greece

central mediterranean explosive volcanism and tephrochronology during the last 630 ka based on the sediment record from lake ohrid abstract lake ohrid located in the central mediterranean region downwind of the italian volcanoes has great potential for developing a detailed record of the explosive activity of these volcanoes electron microprobe and laser ablation inductively coupled plasma mass spectrometry geochemical analyses of juvenile glass fragments of previously not analysed tephra layers of the deep site sediment record of lake ohrid expand the existing tephrostratigraphy for the interval marine isotope stages 1 16 the geochemical signatures of all tephra layers suggest an origin exclusively from the italian volcanism eight of these tephra layers have potential equivalents in marine and terrestrial archives of the central mediterranean region oh dp 1966 sc5 a7 oh dp 1955 ces1 a2 oh dp 1055 s1 oh dp 1006 s2 oh dp 0997 s3 oh dp 0710 s8 c 51 oh dp 0766 odp5 p 13 oh dp 0505 odp4 nine tephra layers which have not been described so far help to reconstruct the late volcanic activity of mount vulture oh dp 2439 and the paleovulsini oh dp 1998 the pre and post rio rava activity of the roccamonfina volcano oh dp 1911 1812 1733 1640 1527 the early activity of the aeolian arc oh dp 1513 1520 and the bracciano activity of the monti sabatini volcanic district oh dp 1175 the multi proxy dataset and chronology of the deep site sediments allowed definition of the climatostratigraphic position for all tephra layers and constrain the ages of so far unknown and or undated tephra layers the presented data provide a crucial increase of knowledge of the middle pleistocene tephrostratigraphy in the central mediterranean back to 630 ka and allows new insights of the volcanic activity of roccamonfina the roman province the campanian volcanic zone cvz the aeolian arc pantelleria and mount vulture

volcanological and petrological evolution of the eastern vulsini district central italy on the basis of recent field mapping data stratigraphic reconstruction and k ar datings a volcanological and petrological study of the bolsena and montefiascone volcanic zones eastern vulsini district has been carried out ten main eruptive phases with both effusive and explosive activity have been recognized these are characterized by a large range of magma compositions belonging to the leucitite basanite and shoshonite magmatic series within each series near primary magmas and slightly to strongly differentiated products are present although in different proportions the great majority of differentiated products mostly trachytic outcrops in the northern sectors of the eastern vulsini district bolsena volcanic zone where lavas or pyroclastics were erupted during moderate to large volume plinian type and ignimbrite forming explosive activity by contrast abundant rather undifferentiated magmas are more frequently found in the southern sectors of the eastern vulsini district montefiascone volcanic zone the structural setting of the sedimentary substratum as well as its lithological characteristics may have played an important role in producing this magma distribution the very shallow position a few hundred meters below the topographic surface of the top of the fracturated carbonate basement would have facilitated the uprising of abundant less evolved magmas in the montefiascone volcanic zone whereas relatively large magma bodies a few kilometer deep can only be inferred in the bolsena volcanic zone bolsena caldera where a front of overthrust sheets of the tuscan and umbrian sedimentology sequences is most probably present in this area source vents of explosive activity show a tendency to shift northeastward with time feeding systems were also differently oriented e w and wnw ese in the southern sectors and nw se and nnw sse in the northern sectors while a ns system was related to a late stage activity of the whole eastern vulsini district

seasonal changes in silica deposition in hot spring systems abstract monthly monitoring of water chemistry at octopus spring yellowstone national park reveals no changes in the chemical composition over this eight month study differences in silica deposition are attributed to flow dynamics and seasonal air temperatures colder air temperatures in winter promote visible accumulation of siliceous sinter probably as a result of decreased solubility periodic drying promotes accumulation and subsequent dehydration of the silica this combination of intermittent supply and periodic dehydration may account for the laminated siliceous deposits observed in the geological record the processes described herein are important in the siliceous preservation of microbial fossils but the following observations underscore the difficulty in preserving microbial fabrics in the geological record pools populated by cyanobacteria are bounded by margins built of silicified microbial mats silicification of the pool margins occurs through an evaporative process called wicking silica rich water is transported upward through the microbial mats by capillary action depositing silica at the surface of the mat as water evaporates the upper surface of such wicking deposits is extremely resistant to brecciation but the underlying support is highly friable and would be difficult to preserve intact in winter months temporary isolation of some pools from active flow causes fragile silica deposition around biological and other debris film coated gas bubbles on the surfaces of microbial mats are observed during all seasons and probably are filled with oxygen released during photosynthesis although this has not been confirmed they become coated with silica during winter months presumably because of increased cooling possibly forming thin discontinuous silica sheets as observed in the geological record