depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

on the formation and propagation of nonlinear internal boluses across a shelf break high resolution two and three dimensional numerical simulations are performed of first mode internal gravity waves interacting with a shelf break in a linearly stratified fluid the interaction of nonlinear incident waves with the shelf break results in the formation of upslope surging vortex cores of dense fluid referred to here as internal boluses that propagate onto the shelf this paper primarily focuses on understanding the dynamics of the interaction process with particular emphasis on the formation structure and propagation of internal boluses onshelf a possible mechanism is identified for the excitation of vortex cores that are lifted over the shelf break from where from the simplest viewpoint they essentially propagate as gravity currents into a linearly stratified ambient fluid

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

isorenieratane record in black shales from the paris basin france constraints on recycling of respired co2 as a mechanism for negative carbon isotope shifts during the toarcian oceanic anoxic event the prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic rich sediments deposited during the toarcian oceanic anoxic event oae has commonly been explained by recycling of 13c depleted co2 the so called kuspert model more recently the massive release of 13c depleted methane or other forms of 13c depleted carbon was also proposed to account for the observed negative 13c excursions in organic carbon of terrigenous as well as of marine origin the occurrence of diagenetic products of the carotenoid isorenieratene isorenieratane and other aryl isoprenoids in toarcian black shales has been regarded as supporting evidence for the kuspert hypothesis as they point to strong stratification of the epicontinental seas a section of a drill core straddling the toarcian of the paris basin cirfontaineen ornois contained intact isorenieratane providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition even prior to the oae however the isorenieratane abundances are very low in the section where the negative 13c excursion in organic carbon and phytane a chemical fossil derived from chlorophyll occurs the abundance of the isorenieratene derivatives increases once the 13c records have shifted to more positive values the 13c of isorenieratane generally circa 13 1 0 5 indicates that the respired co2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7 negative 13c shift recorded in toarcian organic carbon records

instability of exogenous lava lobes during intense rainfall on many volcanoes there is evidence of a relationship between dome collapse and periods of high precipitation we propose a mechanism for this relationship and investigate the conditions that optimize failure by this process observations of elongate lobes that evolve through exogenous growth of lava domes reveal that they commonly develop tensile fractures perpendicular to the direction of motion these cracks can increase in depth by localized cooling and volumetric contraction during periods of high rainfall water can fill these cracks and the increase in fluid pressure on the base of the lobes and within the crack can trigger the collapse of the hot exogenous lava domes using limit equilibrium analysis it is possible to calculate the water and vapor forces acting on the rear and base of the potentially unstable part of the lobe the model presented is rectangular in cross section with material properties representative of andesitic dome rocks vapor pressures at the base of cracks are sealed by the penetrating rainfall which forms a saturated cap within the lobe this leads to an increase in fluid pressurization both through the underlying gas pressure and the downslope component of the liquid water cap fluid pressurization increases as the penetration depth increases this rainfall penetration depth is dependent on the thermal properties of the rocks antecedent temperature lobe geometry and the intensity and duration of precipitation dominant parameters influencing the stability of the lobe are principally lobe thickness duration and intensity of rainfall and antecedent lobe temperature our modeling reveals that thicker lobes are intrinsically more unstable due to the amplification of downslope forces in comparison to cohesive strength the increase in the duration and intensity of rainfall events also increases the potential for collapse as it leads to deeper liquid penetration deeper penetration depths are also achieved through lower antecedent temperatures since less fluid is lost through vaporization thus the potential for rain triggered collapse increases with time from emplacement

toarcian oceanic anoxic event an assessment of global causes using belemnite c isotope records from black shales markingthe toarcian oceanic anoxic event t oae the first explanation envisions recycling of dissolved inorganiccarbon dic with a light isotopic signature into the photic zone from the lower levels of a salinity stratifiedwater mass essentially requiring a regional paleoceanographic driver of the carbon cycle the second involvesthe rapid and massive dissociation of methane from gas hydrates that effectively renders the t oae a globalperturbation of the carbon cycle we present c isotope records from belemnites d

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part i dome shape and internal structure lava domes comprise core carapace and clastic talus components they can grow endogenously by inflation of a core and or exogenously with the extrusion of shear bounded lobes and whaleback lobes at the surface internal structure is paramount in determining the extent to which lava dome growth evolves stably or conversely the propensity for collapse the more core lava that exists within a dome in both relative and absolute terms the more explosive energy is available both for large pyroclastic flows following collapse and in particular for lateral blast events following very rapid removal of lateral support to the dome knowledge of the location of the core lava within the dome is also relevant for hazard assessment purposes a spreading toe or lobe of core lava over a talus substrate may be both relatively unstable and likely to accelerate to more violent activity during the early phases of a retrogressive collapse soufriere hills volcano montserrat has been erupting since 1995 and has produced numerous lava domes that have undergone repeated collapse events we consider one continuous dome growth period from august 2005 to may 2006 that resulted in a dome collapse event on 20th may 2006 the collapse event lasted 3 h removing the whole dome plus dome remnants from a previous growth period in an unusually violent and rapid collapse event we use an axisymmetrical computational finite element method model for the growth and evolution of a lava dome our model comprises evolving core carapace and talus components based on axisymmetrical endogenous dome growth which permits us to model the interface between talus and core despite explicitly only modelling axisymmetrical endogenous dome growth our core talus model simulates many of the observed growth characteristics of the 2005 2006 shv lava dome well further it is possible for our simulations to replicate large scale exogenous characteristics when a considerable volume of talus has accumulated around the lower flanks of the dome model results suggest that dome core can override talus within a growing dome potentially generating a region of significant weakness and a potential locus for collapse initiation

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

monitoring the 2004 andesitic block lava extrusion at volcan de colima mexico from seismic activity and so2 emission the 2004 andesitic block lava extrusion at volcan de colima mexico was accompanied and followed by numerous seismic signals associated with rockfalls pyroclastic flows and explosive events we analyze temporal variations in the number of rockfalls and explosions the seismic signal duration of rockfalls and the energy of the explosion and compare this with both the rate of magma discharge and so2 emission characteristics of seismic signals and so2 emission are compared with those observed during the 1998 1999 volcan de colima block lava extrusion for both eruptions the explosive activity was low during the lava extrusion and increased after its termination the variation in the daily number and the total duration of rockfall seismic signals gives a good reflection of the development of the lava emission process an increase in magmatic degassing so2 flux was observed some days before the onset of lava extrusion the degassing strongly decreased some days before the peak in the rate of the 1998 1999 lava emission but reached its peak together with the peak in the rate of the 2004 lava emission these features of seismic activity and so2 emission demonstrate that they are good tools for monitoring the extrusion process

magma production and growth of the lava dome of the soufriere hills volcano montserrat west indies november 1995 to december 1997 from november 1995 to december 1997 a total volume of 246 106 dre m of andesite magma erupted partitioned into 93 106 m of the dome 125 106 m of pyroclastic flow deposits and 28 106 m of explosive ejecta in the first 11 weeks magma discharge rate was low 0 5 m s from february 1996 to may 1997 discharge rates have averaged 2 1 m s but have fluctuated significantly and have increased with time three pulses lasting a few months can be recognised with discharge rates reaching 3 to 8 m s short term pulsations in growth lasting a few days reach discharge rates of over 10 m s and there are periods of days to a few weeks when dome growth is 0 5 m s discharge rate increased from may 1997 with an average rate of 7 5 m s to december 1997 the observations indicate an open magmatic system

the toarcian radiolarian event in bedded cherts from southwestern japan abstract a drastic faunal turnover of radiolarians in the early toarcian termed the toarcian radiolarian event tre recognized in bedded chert sequences of southwestern japan is marked by the first co appearance of the genus praeparvicingula and mesosaturnalis hexagonus and by high diversity among multicyrtids the event resulted in the replacement of latest triassic through earliest jurassic taxa by late jurassic to early cretaceous taxa at tre levels in bedded cherts in southwestern japan the size of radiolarians decreased drastically reworked conodont fossils appeared and anoxic sediments black cherts with fes2 nodules were deposited the lithologic and faunal changes suggest that global marine environmental changes including the occurrence of anoxia caused the tre

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

meteorological monitoring of an active volcano implications for eruption prediction abstract rainfall data collected on and around the soufriere hills volcano montserrat between 1998 and 2003 were analysed to assess the impact on primary volcanic activity defined here as pyroclastic flows dome collapses and explosions fifteen such rainfall triggered events were identified if greater than 20 mm of rain fell on a particular day the probability of a dome collapse occurring on that day increased by a factor of 6 3 to 9 2 compared to a randomly chosen day similarly the probability of observing pyroclastic flows and explosions on a day with 20 mm of rainfall increased by factors of 2 6 and 5 4 respectively these statistically significant links increased as the rainfall threshold was increased seventy percent of these rainfall induced dome collapse episodes occurred on the same calendar day most within a few hours as the onset of intense rainfall but an extra 3 occurred one or two calendar days later the state of the volcano was important with the rainfall volcanic activity link being strongest during periods of unstable dome growth and weakest during periods of no dome growth or after a recent major collapse over 50 of the heavy rain days were associated with large scale weather systems that can potentially be forecast up to a few days ahead however the remaining heavy rain days were associated with small scale essentially unpredictable weather systems there was significant variability in the amount of rainfall recorded by different rain gauges reflecting topographic variations around the volcano but also the inherent small scale variability within an individual weather system hence any monitoring warning program is recommended to use a network rather than just a single gauge the seasonal cycle in rainfall was pronounced with nearly all the heavy rain days occurring in the may december wet season hence the dome was at its most vulnerable at the beginning of the wet season after a period of uninterrupted growth interannual variability in rainfall was related to tropical pacific and atlantic sea surface temperature anomalies and holds out the prospect of some limited skill in volcanic hazard forecasts at even longer lead times

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

the oceanography of the northern south china sea shelf sea nosocs and its adjacent waters overview and highlights abstract tropical shelf seas constitute a sub set of shelf seas that has not been studied extensively the no rthern so uth c hina sea s helf sea nosocs study is a continuation of the longstanding interest in taiwan on the oceanography of the east asian shelf seas and is an attempt to provide systematic and synoptic observations on a tropical shelf sea the two basic hypotheses in the study are 1 as in the ocean interior the behaviors of the shelf seas vary with latitude and 2 the behaviors of the nosocs are representative of those of the shelf seas in the tropical zone the nosocs has been sampled bi annually in alternating seasons since 2009 the results obtained primarily in 2009 to 2012 are presented here as in the tropical ocean interior a distinguishing characteristic of the nosocs is its shallow mixed layer with depths of about 40 m in the summer and 70 m in the winter as similar mixed layer depths are found in the adjoining northern south china sea scs and they are shallower than the shelf break depth of 120 m the upper nutricline water in the northern scs extends freely into the nosocs and forms a layer of water with significant concentrations of the nutrients immediately below its mixed layer any process that can induce vertical mixing on the shelf may make the nutrients in this subsurface water available for supporting biological activities in the mixed layer in the nosocs such processes include winter convective overturn over the entire nosocs as a result of surface cooling and the strong northeast monsoonal wind winter formation of bottom water in parts of the inner and middle shelf the action of internal waves at the outer shelf and the continental slope and upwelling maintained by wind and or topography the upwelling takes place in the summer off the coasts of dongshan shantou and the northeast coasts of the hainan island but year round at the taiwan bank upwelling over the shelf break is not required for bringing the nutrients in the sub surface waters in the open scs to the nosocs and it was not observed in addition to vertical mixing terrestrial inputs especially through the outflow of the pearl river which reaches its peak in the summer also contribute to the spatial and temporal variations in the composition of the nosocs the combined effects of all these processes lead to a unique seasonal pattern in the variations of the surface concentrations of chlorophyll a in the nosocs with two distinct yearly maxima in the winter and summer

classification and idealized limit equilibrium analyses of dome collapses at soufriere hills volcano montserrat during growth of the first lava dome november 1995 march 1998 abstract styles of dome collapse at soufriere hills volcano shv november 1995 march 1998 are classified by relations between extrusion rate prior to collapse and collapse volume four separate modes of collapse behavior are apparent notably moderate rates of extrusion are shown to result in two disparate modes of collapse small to large collapses on steeply inclined failure planes that switch to collapse volumes an order of magnitude larger that cut deeply into the dome core for constant effusion rates this bifurcation in behavior is explained by the monotonic growth of a soft core that ultimately promotes the development of a deep seated failure over previously favored shallow failure modes models are developed to test this hypothesis that first constrain magnitudes of cohesive and frictional strength with observed dome collapse morphologies and volumes evaluations of dome strengths confirm the important role of a soft core in promoting deep failure a nested model representing a cohesive dome core surrounded by a frictional rind with constant rate of magma input confirms the observed bifurcation in behavior and for invariant effusive activity importantly failure volumes are shown to increase by close to an order of magnitude for a few percent change in the proportion of dome core comprising cohesive material this model is capable of replicating a posteriori the approximate timing of failure for both small 250 m and large 325 m domes the timing and style of the 17 september 1996 and june to november 1997 collapses are honored

rainfall induced volcanic activity on montserrat 1 dome forming volcanic eruptions cyclically extrude bodies of lava over several months which then become gravitationally unstable and collapse generating pyroclastic flows on 29 july 2001 extreme rainfall over montserrat coincided with a major collapse of the soufriere hills lava dome we present rainfall and seismic records that demonstrate for the first time a relationship between intense rainfall and lava dome collapse with associated pyroclastic flow generation after seven months of little rain and a period of sustained dome growth the onset of intense rain was followed within hours by dome collapse and pyroclastic flows the large scale weather system responsible for the rain was identifiable in satellite images and predicted by meteorological forecasts issued 60 hours prior to the volcanic activity it is suggested that weather prediction of intense rainfall be incorporated with existing geophysical and geochemical measurements to improve warnings of these hazardous events

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

recent eruptions at bezymianny volcano a seismological comparison abstract for the past few decades bezymianny volcano has erupted once to twice per year here i examine eight eruptive events between 2006 and 2010 this is the first time period for which proximal or broadband seismic data have been recorded at bezymianny several recurring patterns are demonstrated in advance of eruptions eruptions are generally preceded by 12 36 h of tremor energy elevated by 2 to 3 orders of magnitude locatable earthquake activity is quite erratic in the days before eruptions for eruptions of juvenile magma however the cumulative moment magnitude increases with the repose time since the previous eruption though tenuous this relationship is statistically significant and could improve forecasts of bezymianny eruptions the most energetic eruptions demonstrate increasing multiplet activity in the run up followed by a rapid cessation at the time of eruption when present this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting very long period seismicity 20 s periods accompanies some eruptions these tend to be the same short lived high energy eruptions that exhibit multiplet precursors four eruptions are examined in detail to illustrate the variety in eruption mechanisms lava dome collapses sustained eruptions singular paroxysmal explosions and post explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating bezymianny compared to bezymianny s fifty year modern history recent eruptions have been shorter lived and separated by longer repose times some evidence suggests that these eruptions may be increasingly explosive a speculation that carries significant hazard implications if true however this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors suggesting an ability to improve the already excellent eruption forecasts available for bezymianny

probabilistic analysis of rockfall frequencies during an andesite lava dome eruption the soufriere hills volcano montserrat 1 a probabilistic analysis of rockfalls has been undertaken using seismometer determined information on the timing and duration of rockfalls from the soufriere hills lava dome montserrat between 1995 and 1997 repose intervals between rockfalls fit log logistic survivor distributions differences in the log logistic survivor function for different sub sets of data are accommodated by variation of the parameter k which varies from 0 7 to 1 6 and sample median when extrusion rate is assumed to be 0 m3 s k is 1 denoting that the hazard function has a continuously decreasing form contrasting to the hazard maximum present during periods of extrusion this analysis illustrates a direct relationship between k and lava extrusion rate extrusion rate becomes increasingly significant in determining rockfall frequencies when rates are relatively high whereas other factors become increasingly significant when rates are low

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part ii rockfall activity and talus deformation abstract during many lava dome forming eruptions persistent rockfalls and the concurrent development of a substantial talus apron around the foot of the dome are important aspects of the observed activity an improved understanding of internal dome structure including the shape and internal boundaries of the talus apron is critical for determining when a lava dome is poised for a major collapse and how this collapse might ensue we consider a period of lava dome growth at the soufriere hills volcano montserrat from august 2005 to may 2006 during which a 100 10 6 m 3 lava dome developed that culminated in a major dome collapse event on 20 may 2006 we use an axi symmetrical finite element method model to simulate the growth and evolution of the lava dome including the development of the talus apron we first test the generic behaviour of this continuum model which has core lava and carapace talus components our model describes the generation rate of talus including its spatial and temporal variation as well as its post generation deformation which is important for an improved understanding of the internal configuration and structure of the dome we then use our model to simulate the 2005 to 2006 soufriere hills dome growth using measured dome volumes and extrusion rates to drive the model and generate the evolving configuration of the dome core and carapace talus domains the evolution of the model is compared with the observed rockfall seismicity using event counts and seismic energy parameters which are used here as a measure of rockfall intensity and hence a first order proxy for volumes the range of model derived volume increments of talus aggraded to the talus slope per recorded rockfall event approximately 3 10 3 13 10 3 m 3 per rockfall is high with respect to estimates based on observed events from this it is inferred that some of the volumetric growth of the talus apron perhaps up to 60 70 might have occurred in the form of aseismic deformation of the talus forced by an internal laterally spreading core talus apron growth by this mechanism has not previously been identified and this suggests that the core hosting hot gas rich lava could have a greater lateral extent than previously considered

thin fine grained storm layers in a muddy shelf sequence an example from the lower jurassic in the stenlille 1 well denmark thin storm sand layers are a characteristic feature of many sandy shelf sequences while little evidence of storm layers is preserved in muddy shelf deposits where bioturbation is often total the present study shows that storm generated depositional processes governed sedimentation in a muddy shelf environment the studied sequence is dominated by blackish mudshale and silt streaked mudshale with thinner intervals of pale fine grained heterolithic sandstone it represents the lower jurassic fjerritslev formation in the eastern part of the danish basin and has been studied in four cores from the stenlille 1 well within the muddy outer shelf association four sedimentary facies and 14 types of laminae 0 5 10 mm thick may be distinguished most of the laminae share the characteristics of graded bedding erosive bases and occasional fading ripples with storm layers of sand grade the structures indicate that the mudshale laminae formed by settling of the suspension load carried by storm generated currents this kind of episodic deposition of fine grained storm layers may be common though rarely preserved in outer shelf environments

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

slope instabilities in dolomieu crater reunion island from seismic signals to rockfall characteristics 1 the seismic signals of hundreds of rockfalls within dolomieu crater piton de la fournaise volcano reunion island have been analyzed to investigate a possible link between physical rockfall generating processes and associated seismic signal features moreover indirect observation of rockfalls via the seismic signals they generate can provide useful data for studying volcanoes and the temporal variations of their structure an increase in the number of rockfall events and their volumes might be an indicator of structural weakness and deformation of the volcano associated with potential eruptive activity the study focuses on a 10 month period following the 6 april 2007 crater floor collapse within dolomieu crater from may 2007 to february 2008 for granular flows a scaling law is revealed between seismic energy and signal duration a semiempirical approach based on both analytical analysis and numerical simulation of these flows shows that a similar scaling law exists between the difference of potential energy computed for an event and its propagation times and also emphasizes the effect of local topography on this scaling law simulated and observed data were compared to evaluate the proportion of potential energy dissipated in the form of seismic waves and confirm a direct link between the seismic energy and potential energy of a given granular flow the mean ratio of seismic to potential energy is of the order of 10 4 comparable to the range of values observed in previous studies a simple method based on these ratios is proposed to estimate the volumes of rockfalls from their seismic signal observed seismic energy and the frequency of rockfalls decreased at the beginning of the studied period and reached a stable level in july thus suggesting a postcollapse relaxation time of dolomieu crater structure of about 2 months from seismic signal analysis which is confirmed by deformation data the total rockfall volume over the study period is estimated to be 1 85 mm3

generation of block and ash flows during the 1990 1995 eruption of unzen volcano japan processes generating block and ash flows by gravitational dome collapse merapi type pyroclastic flow were observed in detail during the 1990 1995 eruption of unzen volcano japan two different types were identified by analysis of video records and observations during helicopter flights most of the block and ash flows erupted during the 1991 1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes the mass around the crack became unstable locally decreasing in tensile strength finally a slab separated from the lobe front fragmented progressively from the base to the top within a few seconds and became a block and ash flow rock falls immediately followed in response to local instability of the lobe front clasts in these rock falls fragmented and merged with the preceding flow in contrast block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows

instability and collapse of hazardous gas pressurized lava domes an important type of gravitational lava dome failure involves significant internal gas overpressure that influences the failure process for the first time this paper presents a rigorous analysis of the mechanics of gas pressurized dome failure we develop diffusion models to calculate gas overpressures in a lava dome and embed these pressure data into stability analyses to demonstrate how gas pressurization can initiate instability the results bear on the mechanistic understanding of hazardous dome failures gas pressurization can promote deep seated failure and the timing of conduit pressurization can control the timing of dome collapse theory explains why dome collapse can be delayed for cases of oscillating effusion dome collapses and explosive events linked to collapse of lava domes can be hazardous monitoring criteria are considered to anticipate whether or not such collapses are likely to be explosive

a marine biogeochemical perspective on black shale deposition abstract deposition of marine black shales has commonly been interpreted as having involved a high level of marine phytoplankton production that promoted high settling rates of organic matter through the water column and high burial fluxes on the seafloor or anoxic sulfidic water column conditions that led to high levels of preservation of deposited organic matter or a combination of the two processes here we review the hydrography and the budgets of trace metals and phytoplankton nutrients in two modern marine basins that have permanently anoxic bottom waters this information is then used to hindcast the hydrography and biogeochemical conditions of deposition of a black shale of late jurassic age the kimmeridge clay formation yorkshire england from its trace metal and organic carbon content comparison of the modern and jurassic sediment compositions reveals that the rate of photic zone primary productivity in the kimmeridge sea based on the accumulation rate of the marine fraction of ni was as high as 840 g organic carbon m 2 yr 1 this high level was possibly tied to the maximum rise of sea level during the late jurassic that flooded this and other continents sufficiently to allow major open ocean boundary currents to penetrate into epeiric seas sites of intense upwelling of nutrient enriched seawater would have been transferred from the continental margins their present location onto the continents this global flooding event was likely responsible for deposition of organic matter enriched sediments in other marine basins of this age several of which today host major petroleum source rocks bottom water redox conditions in the kimmeridge sea deduced from the v mo ratio in the marine fraction of the kimmeridge clay formation varied from oxic to anoxic but were predominantly suboxic or denitrifying a high settling flux of organic matter a result of the high primary productivity supported a high rate of bacterial respiration that led to the depletion of o2 in the bottom water a high rate of burial of labile organic matter albeit a low percentage of primary productivity in turn promoted anoxic conditions in the sediment pore waters that enhanced retention of trace metals deposited from the water column

electron microscope analysis of zoned dolomite rhombs in the jet rock formation lower toarcian of the whitby area u k zoned dolomite rhombs which occur in the organic rich jet rock formation toarcian of northeast england have been studied using backscattered scanning electron microscopy transmission electron microscopy and energy dispersive x ray microanalysis the rhombs which are 5 20 m in size are variable in chemical composition but many consist of a dolomite core surrounded by a zone of ferroan dolomite ankerite or ferroan calcite zoned rhombs occur in early diagenetic calcite cemented concretions and layers as well as dispersed throughout the shales distributional and textural evidence suggests that they formed mainly by primary precipitation from pore fluids within the zone of bacterial sulphate reduction the ferroan outer zones probably formed after burial below the sulphate reduction zone when insufficient h 2 s was available to react with all the fe 2 in solution

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

a revised sea level curve for the early jurassic a comparison is undertaken of three different methods of eustatic sea level analysis 1 shallowing and deepening transgressive events inferred from the facies sequence 2 changes through time in the areal spread of epicontinental seas 3 seismic stratigraphy the results of these methods are compared mainly with reference to the lower jurassic new data are brought forward from several continents in a stage by stage study and it is concluded that thelias was characterized by interrupted sea level rise with no major regressions both the transgressions and regressions were relatively rapid with the major transgressions associated with widespread anoxic bottom waters estimates of the net amount of sea level rise through early jurassic time range from 75 m to 110 m

mudstone lithofacies in the kimmeridge clay formation wessex basin southern england implications for the origin and controls of the distribution of mudstones abstract lithofacies analysis has been undertaken on a suite of apparently monotonous organic rich mudstones from the upper jurassic kimmeridge clay formation kcf in the wessex basin southern england using a combination of hand specimen description whole rock geochemistry optical petrography and electron optical petrography five lithofacies have been identified these are clay rich mudstones silt rich mudstones nannoplankton rich mudstones laminated mudstones and concretionary carbonates these facies can be distinguished from one another on the basis of physical sedimentary structures and the relative proportions of allochthonous autochthonous and diagenetic components in each all five of the kcf lithofacies studied were deposited in a marine shelf environment below fair weather wave base but in relatively shallow water close to storm wave base deposition occurred in regions where sand and other coarse clastic allochthonous debris were not being supplied and the bottom waters varied from oxic to anoxic the main factors influencing the development of the five facies were distance from source area primary productivity bottom water anoxia absolute bathymetry clastic dilution and local sediment accumulation rates specifically the clay rich mudstones were deposited in regions farthest down the sediment transport paths commonly in areas by passed by the main sediment supply and beneath surface waters of relatively low primary productivity in contrast the silt rich mudstones were deposited in more proximal areas closer to the source of the sediment in regions where surface productivity and sediment accumulation rates were much higher the nannoplankton rich mudstones accumulated beneath regions where productivity in the surface water layers was fairly high dominated by coccolithophoroid production and the supply of clastic sediment was insufficient to significantly dilute the autochthonous fraction of the sediment unlike the other facies laminated mudstones were deposited in areas where the bottom waters were anoxic surface productivity was enhanced and local sediment accumulation rates were high the concretionary carbonates were precipitated by diagenetic processes in areas where sediment accumulation rates were very low these facies descriptions have enabled a detailed sedimentological study of the kimmeridge clay formation to relate depositional and diagenetic processes directly to the facies present thereby allowing classical facies analyses to be undertaken on apparently homogeneous mudstone successions

nitrogen isotope evidence for water mass denitrification during the early toarcian jurassic oceanic anoxic event bulk sedimentary nitrogen isotope 15ntot data have been generated from lower jurassic black carbon rich shales in the british isles and northern italy deposited during the early toarcian oceanic anoxic event a pronounced positive 15ntot excursion through the exaratum subzone of the falciferum zone defined by characteristic ammonites in the british isles broadly correlates with a relative maximum in weight percent total organic carbon and in some sections with a negative 13corg excursion upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of 15ntot and parallels may be drawn with quaternary sediments of the arabian sea gulf of california and northwest mexican margin the development of early toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity approximately coincident phenomena include the following a relative climatic optimum realignment of major oceanic current systems and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

spatio temporal evolution of rockfall activity from 2007 to 2011 at the piton de la fournaise volcano inferred from seismic data abstract seismic data have been used to catalog the location and volume of most of the rockfalls that occurred at the piton de la fournaise volcano from may 2007 just after the major collapse of the dolomieu summit crater floor to may 2011 this catalog made it possible to compare the evolution of the number and volume of rockfalls at a high temporal resolution and to investigate their links with eruptions seismicity deformations and rainfalls affecting the piton de la fournaise volcano results show that the purge of unstable areas created by the dolomieu crater floor collapse occurred in two phases a first phase lasting three months during which the intense rockfall activity immediately following the collapse decreased abruptly and a second phase lasting more than two years during which the daily volume of the rockfalls slowly decreased before reaching a steady state a detailed study of 4 time periods including 3 eruptive cycles indicates that strong seismicity can increase the number of rockfalls furthermore when a dike reaches the surface at the summit of the central cone giving birth to an eruption the associated local forcing can in some cases increase the volume of rockfalls possibly by creating or expanding weak zones in most cases this is not observed for dike intrusions that do not reach the surface the newly created weak zones are most often far from the eruptive fissures of the ongoing eruption but close to the location of the next eruption this suggests that these distant zones are also weakened at depth thus creating preferred paths for future dikes propagating toward the surface the impact of rainfall on rockfall activity was also studied given that la reunion island is subject to very intense rainfall events our results show that rainfall can in some cases trigger rockfalls rapidly with response times of less than a day but not systematically and no triggering rainfall threshold was found

seismic characterization of the fall 2007 eruptive sequence at bezymianny volcano russia we examine an eruptive sequence in late 2007 at bezymianny volcano to characterize the magmatic plumbing system and eruption related seismicity earthquake locations reveal seismicity below and offset to the north of the volcano along a tectonic fault based on historical seismicity the magma chamber is postulated to have a top at about 6 km depth minor dome explosions large sub plinian eruptions and dome collapses are analyzed using an automated event classification scheme low frequency tremor interpreted as gas escape and low frequency earthquakes are a dominant proportion of the energy released we also examine multiplet earthquakes whose behavior during the study period changed significantly and systematically before the largest eruption demonstrating the potential of tracking multiplets to assess changing conditions with the conduit

dynamic velocity and seismic characteristics of gravitational rockfalls at the merapi lava dome abstract gravitational instability of discrete lava lobes in an active dome building volcano may generate rockfalls that travel up to hundreds of meters from the summit understanding the behaviour of rockfalls is important for volcanic hazard assessment as rockfalls can precede large dome collapses that generate pyroclastic flows here we investigate the mechanisms trajectory velocity and seismic characteristic of rockfalls at the merapi volcano through high resolution video and seismic spectrum frequency analysis high resolution videos of rockfall events were converted to images for every second and were scaled with a georeferenced 3d point cloud to convert pixels into scaled units on the order of a meter the scaled images were analysed using pixel tracking to investigate the mechanism trajectory and velocity of rockfalls results illustrate that the rockfall mechanisms include gravitational free fall rolling and bouncing airborne rotation and rolling over high friction basal surfaces the dynamic mechanisms of gravitational rockfalls at merapi are strongly controlled by the topography and the condition of the basal surface which is responsible for the continuous fluctuations in rockfall velocity maximum rockfall velocity occurs when rocks become airborne while rotating over the steepest area with velocity up to 90 m s material rolling over gently sloping high friction basal surfaces can significantly reduce the rockfall velocity to 2 m s which then ceases the rock movement our high resolution video documents the relatively short durations of gravitational rockfall events at merapi in the range of 24 61 s and has different time duration with the short period seismic signals as the movement of small rock fragments over sandy area is not detected by seismic signal spectral analysis of seismic frequencies indicates that gravitational rockfalls at merapi are characterized by high frequencies with a range of 4 17 hz this study provides new insights and improves our understanding of the dynamic mechanism of rockfall events at dome building volcanoes

the timing of paleoenvironmental change and cause and effect relationships during the early jurassic mass extinction in europe the early jurassic marine mass extinction is one of several crises thought to coincide with anoxia transgression and warming caused by catastrophic release of gas hydrates however high resolution study of expanded sections in yorkshire england reveal that only the first of these factors is truly coincidental with extinction the well known transgression and large negative carbon isotope perturbation attributed to massive release of methane from gas hydrates occur after these events the anoxic event is developed diachronously in the european area with anoxia developing and fading away earlier in the mediterranean region compared with the nw european record however for a brief interval in the mid semicelatum subzone anoxia was simultaneously developed throughout the european region and it is this time that is marked by extinction of both benthic and pelagic marine fossils the sea level curve is also more complex than hitherto assumed with a minor regression occurring late in the semicelatum subzone shortly after the extinction the toarcian crisis occurred during a phase of global warming but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend

chemical and isotopic methods for confirming the roles of wadis in regional groundwater recharge in a regional arid environment a case study in al ain uae in arid environments groundwater may represent the most important source of water for sustaining life the timing and nature of precipitation may induce infiltration and recharge on a small scale the al ain region uae was chosen and from 1996 to 1997 studies were conducted to illustrate spatial distribution of recharge for groundwater by using chemical and isotopic methods according to the field survey uae can be hydrogeologically classified into five parts mountain area wadis sand dunes inland sabkhas and coastal sabkhas respectively in this report we studied a typical wadi wadi mieshiq area upstream of the wadi it was found that the groundwaters were characterized by low salinity stable isotopes of groundwaters in the wadi were lighter than those of the stream waters in the mountain area since stream water was affected by evaporation before it infiltrated into the ground the isotopes of recharged water into the wadi must have isotopically light values from the results above groundwater along the wadi was mainly derived from not only water from the mountain area but also infiltrated water during the flood period wadis are an important recharge region for groundwater copyright 2001 john wiley sons ltd

magma flow instabilities in a volcanic conduit implications for long period seismicity silicic volcanic eruptions are typically accompanied by repetitive long period lp seismicity that originates from a small region of the upper conduit these signals have the capability to advance eruption prediction since they commonly precede a change in the eruption vigour shear bands forming along the conduit wall where the shear stresses are highest have been linked to providing the seismic trigger however existing computational models are unable to generate shear bands at the depths where the lp signals originate using simple magma strength models presented here is a model in which the magma strength is determined from a constitutive relationship dependent upon crystallinity and pressure this results in a depth dependent magma strength analogous to planetary lithospheres hence in shallow highly crystalline regions a macroscopically discontinuous brittle type of deformation will prevail whilst in deeper crystal poor regions there will be a macroscopically continuous plastic deformation mechanism this will result in a depth where the brittle ductile transition occurs and here shear bands disconnected from the free surface may develop we utilise the finite element method and use axi symmetric coordinates to model magma flow as a viscoplastic material simulating quasi static shear bands along the walls of a volcanic conduit model results constrained to the soufriere hills volcano montserrat show the generation of two types of shear bands upper conduit shear bands that form between the free surface to a few 100 m below it and discrete shear bands that form at the depths where lp seismicity is measured to occur corresponding to the brittle ductile transition and the plastic shear region it is beyond the limitation of the model to simulate a seismic event although the modelled viscosity within the discrete shear bands suggests a failure and healing cycle time that supports the observed lp seismicity repeat times however due to the paucity of data and large parameter space available these results can only be considered to be qualitative rather than quantitative at this stage c 2007 elsevier b v all fights reserved

sedimentation rate dilution preservation and total organic carbon some results of a modelling study abstract a modelling exercise was undertaken to evaluate the positive preservational and negative diluent effects of sedimentation rate sr on the total organic carbon toc content of marine sediments and to use multiple regression analysis of modern data to predict toc data presented show the predicted marine toc using the carbon burial efficiency be versus sr relationship of betts and holland betts j n holland h d 1991 the oxygen content of ocean bottom waters the burial efficiency of organic carbon and the regulation of atmospheric oxygen palaeogeography palaeoclimatology palaeoecology global and planetary change section 97 5 18 calculated for a range of sr water depths primary productivities and four fixed be values the results suggest that the preservation effect of sr only enhances toc at 5 cm ka in oxic regimes after which dilution occurs if carbon supply is held constant above 35 cm ka there is no appreciable difference in toc regardless of whether the sea floor is anoxic or not below 10 cm ka there is a strong divergence in oxic and anoxic toc values observed positive correlations of sr and toc at 5 cm ka are largely an artefact of including sites from shallower depths and or higher productivities multiple regression analysis mra of modern marine sediment data suggests that once re scaled to allow for their non linear effect dissolved oxygen values may be a significant additional variable in determining the toc predicting an approximately 2 5 4 0 times higher toc in anoxic facies compared with fully oxic ones 4 ml l dissolved oxygen all other things being equal the mra also indicates a generally negative partial correlation between carbon delivery flux and be in modern sediments producing a significant moderating effect on the predicted toc

the fast response of volcano seismic activity to intense precipitation triggering of primary volcanic activity by rainfall at soufriere hills volcano montserrat abstract one minute resolution time series of rainfall and seismic data from the soufriere hills volcano montserrat are analysed to explore the mechanism of external forcing of volcanic eruptions by rainfall over three years of activity the real time seismic amplitude rsam shows a narrow statistically significant peak within 30 min after the start of intense rainfall events and a much broader peak with a lag of 6 40 h the classified seismic events indicate that the volcanic response to rainfall begins at the surface and gradually penetrates deeper into the dome as there is an increase in the pseudo magnitude of surface rockfall events including pyroclastic flows with lags from the first 30 min to 40 h long period rockfalls from shallow degassing at lags of 4 and 14 h and long period and hybrid events source depth approximately 1 km with lags at 14 and 24 h after the start of rainfall events there was no rainfall related change in deeper volcano tectonic activity there was no change in the frequency of any type of classified event indicating that the rainfall acts to modulate existing internal processes rather than generating new events itself these robust results are due to many 229 different rainfall events and not just to a few large magnitude cases the rainfall triggered volcanic activity examined here is consistent with a model of fast shallow interactions with rainfall at the dome surface after which a deeper dome collapse follows

thermal hydrologic mechanism for rainfall triggered collapse of lava domes hazardous gravitational collapses involving hot lava domes can be triggered by intense rainfall both in periods of active dome growth and volcanic repose the collapses can evolve into energetic failures involving as much as 90 of the dome or 100 3 10 6 m 3 of dome lava retrogressively removed over several hours under standing such potentially lethal phenomena is vital but traditional explanations for rain induced slope failure are problematic for rainfall on hot typically 400 8c crystalline lava in this paper we quantitatively develop a new thermal hydrologic mechanism that can cause such failures pressure buildup within fissures due to effusive gas trapped by a rain saturated dome carapace results in increased destabilizing forces and the loss of mass strength and ultimately results in failure of the dome our mechanistic models are consistent with field observations and provide a quantification of threshold rainfall intensities and durations required to trigger failure

lava dome growth and mass wasting measured by a time series of ground based radar and seismicity observations range and intensity measurements of the change in summit lava 1 5 10 6 m 3 22 2 avtis range measurements to measure the talus growth 3 9 10 6 m 3 57 and 3 rockfall seismicity to measure the pyroclastic flow deposit volumes 1 4 10 6 m 3 21 which gives an overall dense rock equivalent extrusion rate of about 7 m 3 s 1 these figures demonstrate how efficient nonexplosive lava dome growth can be in generating large volumes of primary clastic deposits a process that by reducing the proportion of erupted lava stored in the summit region will reduce the likelihood of large hazardous pyroclastic flows

lava dome growth and evolution with an independently deformable talus subduction zone volcanism occurs due to partial melting from subducting slabs which generally results in high viscosity magma containing a large amount of volatiles such volcanic eruptions can form a lava dome from which collapse events are a common and important part of their evolution collapse events can have devastating consequences in the form of block and ash avalanche deposits pyroclastic ows surges and the generation of tsunamis if they enter the sea in addition to this once a mass of lava dome has been removed during a collapse event this results in a drop in pressure in the remaining volatile rich magma which may then erupt explosively the internal structure of a lava dome and the extent of the surrounding carapace talus is unknown but likely to be critical for hazard assessment and is the motivation for this research presented is a computational model for the growth and evolution of an endogenous lava dome including an independently deformable talus using the finite element method dome growth is modelled to occur under two time scales continuous dome expansion via the addition of new magma into the molten core interior and relatively instantaneous talus readjustments due to rockfalls and the disintegration of the solid surface the continuous deformation of the dome is modelled as a uid with a yield strength in the talus region while talus deformation is modelled as a granular material that rests at angles below its angle of repose both surfaces dome and core talus interface are displaced using the level set method the model is axi symmetric and assumes that solidi cation and therefore talus growth occurs due to gas exsolution which promotes crystallisation rather than from surface cooling appropriate for intermediate composition lava ows for the purpose of this paper we consider and apply the model to the soufriere hills volcano montserrat but the techniques used are generic allowing the model to be applied to other dome forming eruptions the model provides information on the shape of the dome with the growth and extent of the talus and core found to be predominantly governed by the lava extrusion rate degree of solidi cation i e a solidus pressure the friction angle associated with the talus and lava dome viscosity

toarcian black shales in the dutch central graben record of energetic variable depositional conditions during an oceanic anoxic event the wrong figure was printed in place of figure 4 in the february 2012 issue of jsr p 114 please

carbon isotope stratigraphy and temperature change during the early middle jurassic toarcian aalenian raasay scotland uk abstract the data presented here provide the first high resolution investigation of carbon and oxygen isotope derived from boreal aalenian bajocian belemnites from the isle of raasay scotland uk further isotope data has been gathered from the toarcian the carbon isotope data reveal a positive carbon isotope excursion in the early aalenian scissum zone equivalent to the tethyan comptum subzone the correspondence between this record and tethyan records lends support that this excursion is global in origin although the excursion is coeval with a transgressive interval less obvious is an association with the deposition of organic rich deposits an equivocal excursion toward light isotopic close to the aalenian bajocian boundary may be linked to a major pulse of subduction related magmatism light oxygen isotopes and high temperatures are derived from belemnites from the toarcian falciferum zone akin to coeval data from elsewhere surface waters during the falciferum zone may have been episodically reduced oxygen isotope data from the aalenian are interpreted to show a cooling trend to a minimum at the base in the opalinum scissum zonal boundary this major step in cooling is however not entirely coincident with sea level data and significantly the inferred cooling occurs prior to the positive carbon isotope excursion hence a carbon drawdown and burial scenario that has been interpreted from positive carbon excursions elsewhere cannot drive a precursory cooling episode

significance of lamination in toarcian lower jurassic shales from yorkshire great britain abstract lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes variations in types of lamination in toarcian lower jurassic shales of yorkshire great britain are related to changes in sedimentary processes x radiography petrography and scanning electron microscopy techniques reveal three lamination types in the dark grey grey shales and black jet rock and bituminous shales jurassic shales fine lamination is produced in deeper more offshore anaerobic conditions in which suspension settling dominates thick lamination indicates the influence of bottom flowing currents in shallow water wavy lamination is produced by benthic microbial mats the toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment the examples of various unique macro and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation

discovery of agglutinated benthic foraminifera in devonian black shales and their relevance for the redox state of ancient seas abstract agglutinated foraminifera are benthic organisms that occur in marginal marine to bathyal environments though some taxa can live in oxygen deficient environments they require at least some oxygen in order to persist at the seafloor the discovery that they occur widely in late devonian black shales has a bearing on the boundary conditions required for episodes of extensive carbon sequestration in marine sediments and their connection to atmospheric composition and global climate devonian black shales of the eastern us have been studied extensively to determine the fundamental controls on carbon burial and a range of mechanisms has been proposed finding agglutinated benthic foraminifera in these black shales refocuses the debate about their origin and points to limitations of earlier models

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

effects of an oceanic anoxic event on the stable carbon isotopic composition of early toarcian carbon the early toarcian transgression is marked by the occurrence of organic carbon rich shales in large parts of western europe and in other parts of the world as well based on the positive carbon isotope excursion of pelagic limestones in the middle to upper part of the falciferum zone in several of the tethyan sections the widespread occurrence of the early toarcian shales was explained by an oceanic anoxic event oae jenkyns 1988 jenkyns and clayton 1997 the rapid burial of large amounts of organic carbon which is rich in 12 c would have led to a relative enrichment in 13 c of the global carbon reservoir and hence to an increase in delta 13 c of the limestones in southwest germany and a number of other locations both organic and inorganic carbon display a negative isotope excursion in the upper part of the tenuicostatum zone and the lower part of the falciferum zone synchronous to black shale deposition and predating the positive isotopic excursion kuspert 1982 1983 it is presently unclear what the exact cause for this widespread negative isotopic excursion is jenkyns and clayton 1997 the objective of our study was to examine if the negative carbon isotope excursion of organic matter om in the southwest german toarcian shales can be attributed to compositional changes of the om or if the excursion is related to variations in delta 13 c sub co2 aq in the photic zone to this end we analyzed the molecular and stable carbon isotope composition of om in ten samples spanning the early toarcian toc 2 5 10 5 percent hi 350 700 biomarker distributions and kerogen pyrolysates differ only slightly among the samples and delta 13 c values of primary production markers follow closely those of associated carbonate and kerogen delta 13 c sub carb toc this strongly suggests that differences in delta 13 c toc are related to differences in delta 13 c of co 2 aq in the photic zone supporting kuspert9s model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters evidence for euxinic conditions extending into the photic zone was found by the presence of derivatives of carotenoids such as isorenieratane from anoxygenic phototrophic sulfur bacteria their concentrations are extremely low in black shales from the tenuicostatum zone but are significant in the falciferum and bifrons zone with a maximum in the exaratum subzone suggesting that photic zone euxinia pze was a common feature of the early toarcian sea in southwest germany our data therefore support the kuspert model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters to the upper part of the photic zone resulting in a negative isotope spike the enrichment in 13 c in the middle of the falciferum zone which followed the negative spike may be attributed to the burial of isotopically light organic matter through worldwide black shale deposition