the distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and s w pacific abstract 62 manganese nodules and 17 associated sediments from the equatorial and s w pacific have been analyzed for a number of elements including the rare earth elements ree by instrumental neutron activation sc co as hf th and ree occur in higher concentrations in s w pacific than in equatorial pacific nodules reflecting the higher iron content of the s w pacific nodules these elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure the highest ce la ratios are also found in the s w pacific nodules this may result from the fact that these nodules lie beneath the path of the fast flowing well oxygenated antarctic bottom water aabw which facilitates oxidation of ce to the tetravalent state if so this supports the idea that the ce la ratio of manganese nodules is an important redox indicator negative cerium anomalies were noted for nodules from areas f and g can be interpreted on the same model the ree contents in equatorial pacific siliceous oozes and s w pacific red clays are similar on a carbonate free basis the ce la ratio of the s w pacific red clays is however much higher than that of the equatorial pacific sediments possibly reflecting the preferential oxidation of ce to the tetravalent state beneath the aabw there appears to be no systematic relationship between the ree abundance in the nodules and their associated sediments although absolute ree abundances are higher in nodules than in their associated sediments nodules with the highest ce la ratios are however found on sediments with the highest ce la ratios the principal difference in the ree distribution pattern of the nodules and sediments lies in the well known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments

on abandoning the thunderstorm tripole charge paradigm we reexamine the original half century old in situ measurements of simpson and colleagues used to justify the tripole model of charge structure of a thunderstorm that became the paradigm for the charge structure of mature thunderstorms we find that the original measurements violate the criteria of the tripole model in 49 of the cases we also reexamine our soundings of electric field in thunderstorms and mesoscale convective systems in the same way as the original soundings were our soundings do not fit the tripole model in at least 86 of the storms even when we consider only the major features in the electric field profiles our data show noncompliance with the tripole model in 45 of the cases we conclude that we must abandon the paradigm of the tripole charge structure of thunderstorms

hydrothermal activity in the se tyrrhenian sea an overview of 30 years of research subduction related volcanic activity in the southeast tyrrhenian back arc basin has resulted in a large variety of calcalkaline rocks ranging from arc tholeiitic to shoshonitic and rhyolitic composition which were emplaced in both oceanic and continental crust hydrothermal systems in the se tyrrhenian sea have leached these magmatic rocks generating a wide range of oxyhydroxide and sulfide deposits all the hydrothermal occurrences formed at much shallower depths than those from the mid ocean ridges oxyhydroxide deposits metalliferous sediments crusts and nodules are almost pure hydrothermal formations with insignificant hydrogenetic and diagenetic contributions they exhibit strong separation of mn rich and fe rich end members with mn rich occurrences dominant their geochemistry suggests a relative enrichment of mn in the hydrothermal systems of the se tyrrhenian the sulfides are zn and pb rich but poor in cu and relatively poor in fe this suggests either deep seated magma chambers or boiling of the hydrothermal fluids beneath the seafloor as a consequence 1 cu and a large proportion of the fe are deposited as sulfides in the basement rocks and sediment cover 2 the hydrothermal fluids become relatively enriched in mn zn and pb a number of accessory sulfosalts and selenides not typical of mid ocean ridge massive sulfides are present

the aluminosilicate fraction of north pacific manganese nodules abstract nine nodules collected from throughout the deep north pacific were analyzed for their mineralogy and major element composition before and after leaching with chester hughes solution data indicate that the mineral phillipsite accounts for the major part 75 of the aluminosilicate fraction of all nodules it is suggested that formation of phillipsite takes place on growing nodule surfaces coupled with the oxidation of absorbed manganous ion all the nodules could be described as ternary mixtures of amorphous iron fraction fe ti p manganese oxide fraction mn mg cu ni and phillipsite fraction al si k na these fractions accounting for 96 of the variability of the chemical composition

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

effects of charge and electrostatic potential on lightning propagation 1 three dimensional lightning mapping observations are compared to cloud charge structures and electric potential profiles inferred from balloon soundings of electric field in new mexico mountain thunderstorms for six individual intracloud and cloud to ground flashes and for a sequence of 36 flashes in one storm the comparisons consistently show good agreement between the altitudes of horizontal lightning channels and the altitudes of electric potential extrema or wells lightning flashes appear to deposit charge of opposite polarity in relatively localized volumes within the preexisting lower positive midlevel negative and upper positive charge regions associated with the potential wells the net effect of recurring lightning charge deposition at the approximate levels of potential extrema is to increase the complexity in the observed storm charge structure the midlevel breakdown of both normal intracloud flashes and negative cloud to ground flashes is observed to be segregated by flash type into the upper and lower parts of the deep potential well associated with the midlevel negative charge the segregation is consistent with perturbations observed in the bottom of the negative potential well due to embedded positive charge that was probably deposited by earlier flashes it is also consistent with an expected tendency for vertical breakdown to begin branching horizontally before reaching the local potential minimum the joint observations reconcile the apparent dichotomy between the complex charge structures often inferred from balloon soundings through storms and the simpler structures often inferred from lightning measurements

horizontal distribution of electrical and meteorological conditions across the stratiform region of a mesoscale convective system abstract five soundings of the electric field and thermodynamic properties were made in a mesoscale convective system mcs that occurred in oklahoma and texas on 2 3 june 1991 airborne doppler radar data were obtained from three passes through the stratiform echo from these electrical kinematical and reflectivity measurements a conceptual model of the electrical structure of an mcs is developed low level reflectivity data from the storm s mature and dissipating stages show typical mcs characteristics the leading convective region is convex forward and the back edge of the stratiform echo is notched inward the maximum areal extent of the low level echo is about 250 km 550 km and the radar bright band is intense reflectivity 45 50 dbz through an area of at least 50 km 100 km the reflectivity above the bright band is horizontally stratified with decreasing intensity and echo top height toward the rear of the system analyses of the velocity data reveal a convective line relative flow struct

mud volcanoes revealed and sampled on the western moroccan continental margin we surveyed and sampled two active and 3 inactive mud volcanoes on the atlantic continental margin of morocco the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise between 150 250 meters above the seafloor and are the first active methane related mud volcanoes to be identified in this region the inactive volcanoes range in diameter from 1 3 km with relief between 50 and 80 meters gravity cores from the crest of the active mud volcanoes yielded methane hydrates and mud breccia deposits chemosynthetic communities of pogonophora worms and the bivalve solemya were found on the surface of the active mud volcanoes sediment cores from the inactive volcanoes contained hemipelagic sediments rich in foraminifera and ahermatypic coral debris overlying mud breccia

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

gas charged sediments and large pockmark like features on the gulf of cadiz slope sw spain abstract gassy sediments and large seafloor pockmarks are identified from seismic profiles in the gulf of cadiz slope gas charged sediments are represented by zones of acoustic turbidity and other acoustic anomalies on seismic profiles most of the gas is believed to be biogenic in origin resulting from the decay of organic matter contained within rapidly developed regressive shelf margin deltas a group of large asymmetric seafloor pockmarks also occurs downslope of the gassy area both on the seafloor surface and deeply buried in the sediment column sediment sorting by the mediterranean undercurrent seems to act as a controlling factor for the development of each type of gas originated feature the area where the strong mediterranean undercurrent outflow impinges the seafloor is covered by sandy sediments of high porosity which allow the interstitial gas to escape through the sediment pores whereas the areas affected by weaker currents are covered by clays and the gas tends to accumulate in the sediment beneath impermeable horizons

microchemical characterisation of natural gold and artefact gold as a tool for provenancing prehistoric gold artefacts a case study in ireland the importance of au to ancient societies has encouraged many archaeologists to search for the sources exploited in antiquity these projects generally involve detailed studies of artefacts and comparison of their chemical characteristics with those reported for natural au however descriptions of natural au are frequently inadequate for provenancing studies and the compositional variability of the material is not widely recognised the present study describes a new approach to gold provenancing using the technique of microchemical characterisation in which populations of gold grains are classified according to the alloy compositions and the assemblages of microinclusions of other minerals this technique originally developed to identify sources of alluvial gold during au exploration has proved applicable to provenancing studies in four main areas firstly microchemical characterisation of artefacts grouped according to archaeological criteria can indicate the number of sources exploited in relation to time and artefact taxonomy secondly knowledge of the total variation in chemical characteristics of natural au from a particular region provides an excellent database for provenancing and reduces the need for exhaustive sampling thirdly it is possible to predict how au alloys were modified during fabrication as a consequence of assimilation of mineral inclusions finally identification of inclusion phases in artefact au can provide information on metallurgical practices these principles have been applied to the search for the source of au used for the unique traditions of prehistoric irish metalworking studies of 180 irish au artefacts belonging to four major metalworking traditions dating from the early bronze age 2400 bc to the iron age 150 bc show that each group exhibits distinctive ag and cu contents parallel studies of 2267 natural au grains from 58 alluvial localities and four bedrock localities throughout ireland reveal a broad pattern of alloy compositions consistent with style of mineralisation and host geology the ranges of ag contents of early bronze age and middle bronze age artefacts suggests that the au source lies within lower palaeozoic sedimentary rocks of the southern uplands terrane and significantly that the same source or sources were used in both periods a different source of relatively ag rich au most probably at croagh patrick co mayo was exploited in the late bronze age iron age artefacts have ag contents higher than natural irish au evidence for evolution of metallurgical practice during the bronze age is provided by the increasing cu content of the gold alloys to levels far in excess of natural gold and the nature of inclusions in artefacts of different ages elevated sn in cu rich alloys suggests deliberate or accidental alloying with bronze this approach has provided the first clear indication that only a few individual indigenous irish sources of au were used during the bronze age and that their relative importance changed over time future archaeological investigations may adopt a geographical focus that was not previously possible

observations of volcanic lightning during the 2009 eruption of redoubt volcano abstract observations of volcanic lightning during the eruption of redoubt volcano in march and april 2009 were made with the lightning mapping array during the eruption twenty three distinct episodes of volcanic lightning were observed electrical activity occurred as either a volcanic lightning storm with up to thousands of lightning discharges or as a weak electrical event with only a handful of lightning discharges during the volcanic lightning storms we observed two phases of electrical activity the explosive phase and the plume phase the explosive phase consisted of very small discharges on the order of 10 100 m occurring directly above the vent while an explosive eruption was ongoing whereas the plume phase was comprised of discharges occurring throughout the plume subsequent to the explosive eruption the area of discharges during the explosive phase ranged from less than 1 km2 to 50 km2 or more the electrical activity at the beginning of the plume phase was dominated by small discharges over time the horizontal extent of the flashes increased with the largest flashes occurring at the end of the plume phase the distribution of the horizontal size of the discharges over the lifetime of the storm indicate that the charge structure of the plume evolved from a complex and clumpy structure to a more simple horizontally stratified structure plume height was shown to be a key factor in the quantity of lightning in a storm the volcanic lightning storms occurred in plumes with column heights greater than 10 km the tall plumes may contribute to the efficiency of charge generation through ice collisions by providing strong updrafts from the large thermal energy input from the eruption

kinematic and precipitation structure of the 10 11 june 1985 squall line abstract high frequency 90 min rawinsonde data from a special mesoscale network 26 sites have been combined with wind profiler dense automated surface network data 80 stations spaced 50 km apart and a series of high resolution dual doppler radar analyses in a common framework attached to a moving squall line system to form a comprehensive dataset describing the mature phase of the 10 11 june 1985 squall line observed during pre storm the dual doppler radar analyses covered a 200 300 km2 area from the leading edge of the convective line to the back edge of the trailing stratiform precipitation region thus providing high resolution wind information over a very broad portion of the storm system the comprehensive analysis is used to resolve several aspects of the trailing stratiform region that had remained unclear from previous studies first a difference in the horizontal scale was found between the mesoscale updraft which at upper levels was on the scale of the trailing stratiform cloud a

electrical structure in thunderstorm convective regions 3 synthesis in this paper results from nearly 50 electric field soundings through convective regions of mesoscale convective systems mcss isolated supercells and isolated new mexican mountain storms are compared and synthesized these three types of thunderstorm convection are found to have a common basic electrical structure within convective updrafts the basic charge structure has four charge regions alternating in polarity and the lowest is positive outside updrafts of convection there are typically at least six charge regions alternating in polarity and the lowest is again positive among the three storm types there are differences in the heights and temperatures at which the basic four charge regions are found in updrafts the height temperature of the center of the main negative charge region averages 6 93 km 16 c in mcs convective region updrafts 9 12 km 22 c in supercell updrafts and 6 05 km 7 c in new mexican mountain storm updrafts in updraft soundings through all three storm types the center height of the main negative charge region increases with increasing average balloon ascent rate and updraft speed at a rate of about 0 3 km per 1 m s 1 with a correlation coefficient of 0 94 a schematic illustrates the basic four and six charge structure for thunderstorm convective regions and it is offered as an improved model for thunderstorm charge structure

fast growing shallow water ferro manganese nodules from the western baltic sea origin and modes of trace element incorporation abstract ferro manganese nodules of the western baltic sea reveal enhanced heavy metal concentrations since the end of the 19th century and are therefore potentially useful for retrospective monitoring of the heavy metal pollution history however only zn shows a significant rise even though cu is also introduced to the western baltic sea by natural and anthropogenic sources this study focused on geochemical considerations to evaluate the mechanism responsible for the predominance of zn in ferro manganese nodules compared to cu the particulate and dissolved metal fractions in the water column in the fluffy layer an approximately 2 cm thick sediment layer situated at the sediment water interface and in the pore water adjacent to ferro manganese nodules were studied the analysis of the dissolved fraction and speciation studies were carried out using cathodic stripping voltammetry csv the particulate fraction and the pore water were analyzed via graphite furnace atomic absorption spectroscopy gf aas and inductively coupled plasma optical emission spectroscopy icp oes the fluffy layer provides high quantities of mn fe zn and cu to the dissolved fraction of the bottom water during the stratification period hence the signal manifested in the ferro manganese nodules consists of newly emitted elements on top of the amount collected in the fluffy layer over many years and remobilized throughout the stratification trace elements with the tendency to form weak inorganic complexes in the water column like zn are more likely to be incorporated in ferro manganese nodules and therewith document the anthropogenic metal input while elements which tend to form strong organic complexes such as cu are scavenged by particulate organic matter in the water column and the fluffy layer

seismotectonics of portugal and its adjacent atlantic area abstract a study of focal mechanisms of earthquakes and stress indicators are presented for portugal and its adjacent atlantic margins recently riberio et al 1996 published a work on this subject in this study we introduce new focal mechanisms of nine earthquakes we use these results together with 12 other focal mechanisms and the main tectonic features in the region to define more accurately the type of mechanism and the stress pattern of the region all the focal mechanisms used in this study differ partially but are compatible with the regional stress field the stress indicators resulting from focal mechanisms and other geological and geophysical data show that the portugal continental and its atlantic margins are under horizontal pressure in nnw sse direction with a greater proportion of strike slip and reverse oblique mechanisms for the whole area

flash propagation and inferred charge structure relative to radar observed ice alignment signatures in a small florida mesoscale convective system a series of vertical cross sections taken through a small mesoscale convective system mcs observed over florida by the dual polarimetric smart radar were combined with vhf radiation source locations from a lightning mapping array lma to examine the lightning channel propagation paths relative to the radar observed ice alignment signatures associated with regions of negative specific differential phase kdp additionally charge layers inferred from analysis of lma sources were related to the ice alignment signature it was found that intracloud flashes initiated near the upper zero kdp boundary surrounding the negative kdp region the zero kdp boundary also delineated the propagation path of the lightning channel with the negative leaders following the upper boundary and positive leaders following the lower boundary very few lma sources were found in the negative kdp region we conclude that rapid dual polarimetric radar observations can diagnose strong electric fields and may help identify surrounding regions of charge

large scale slope failure involving triassic and middle miocene salt and shale in the gulf of cadiz atlantic iberian margin sheets of salt and ductile shale advancing beyond the thrust front of the gibraltar arc iberian moroccan atlantic continen tal margin triggered downslope movements of huge allochth onous masses these allochthons represent the cadiz nappe which detached from the gibraltar arc along low angle normal faults and migrated downslope from the iberian and moroccan continental margins towards the atlantic ocean extensional tectonics initiated upslope salt withdrawal and downslope diapirism during large scale westward mass wasting from the shelf and upper slope low angle salt and shale detachments bound by lateral ramps link extensional structures in the shelf to folding thrusting and sheets of salt and shale in the gulf of cadiz from backstripping analyses carried out on the depo centres of the growth fault related basins on the shelf we infer two episodes of rapid subsidence related to extensional collapses these were from late tortonian to late messinian 200 400 m myr 1 and from early pliocene to late pliocene 100 150 m myr 1 the extensional events that induced salt movements also affected basement deformation and were probably associated with the westward advance of frontal thrusts of the gibraltar arc as a result of the convergence between africa and eurasia the complexities of salt and or shale tectonics in the gulf of cadiz result from a combination of the deformations seen at convergent and passive continental margins

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

the application of microchemical analysis of alluvial gold grains to the understanding of complex local and regional gold mineralization a case study in the irish and scottish caledonides terranes of the appalachian caledonian orogen north of the iapetus suture host gold mineralization in north america scotland and ireland to date commercial exploitation has been confined to the appalachian terrane of canada in scotland and ireland regional analysis of the types of gold mineralization has been handicapped by the relatively small number of bedrock gold occurrences available for study however there are a large number of alluvial gold localities a technique of microchemical characterization of gold grains has been applied to facilitate the classification of alluvial gold localities in terms of the style or styles of source mineralization thereby permitting a more complete interpretation of regional gold mineralization the technique of microchemical characterization used in this study classifies populations of gold grains from each locality in terms of the assemblage of opaque mineral inclusions enclosed within the gold grains and the concentration of minor alloying elements in the gold a total of 2 400 gold grains collected from 44 sites in ireland and scotland have been studied the microchemical signatures of populations of gold grains extracted from bedrock samples correlate closely with those from adjacent alluvial populations and furthermore our data are compatible with the descriptions of the vein mineralogy of bedrock mineralization reported by other workers this result has facilitated informed speculation on the type of source mineralization of other alluvial occurrences where the bedrock source remains undiscovered populations of alluvial gold from individual localities have been grouped into larger regional data sets on the basis of similarities in microchemical signature the signatures of these data sets were analyzed using the same criteria and 10 classes of gold were identified regional analysis of the distribution of the gold classes showed that the occurrence of the four major classes correlates strongly with host terrane irrespective of geographical location gold from the southern uplands terrane is characterized by inclusions of base metal sulfides and sulfarsenides with the silver content of the gold being less than 15 percent in contrast populations of alluvial gold from the grampian and highland terranes commonly exhibit median silver contents of over 20 percent and frequently contain silver telluride and bismuth telluride inclusions which are extremely rare in gold from the southern uplands terrane however in other cases the style of mineralization is controlled by specific host or source rocks and is independent of the terrane two examples are gold mineralization within porphyry systems and gold associated with red bed sediments the study has confirmed the value of the technique of gold grain characterization using information from both concentrations of alloying elements and inclusion assemblages as a powerful tool in interpreting complex local and regional gold mineralization

holocene methane derived dolomite cemented sandstone pillars from the kattegat denmark abstract dolomite cemented sandstone pillars up to 4 m high and 1 m in diameter are recorded from 10 12 m of water in the kattegat denmark the framework of the sandstone pillars is similar to that of the adjacent sediments i e medium grained well sorted quartz sand the carbonate cement consists of equicrystalline ca rich dolomite mg47 ca53 co3 10 30 m in diameter exhibiting a sucrosic texture the sr content is relatively constant at approximately 1000 ppm whereas the fe and mn contents are highly variable with mean values of 1870 and 320 ppm respectively the carbon isotopic signature of the dolomite cement displays negative 13c values in the range of 44 to 40 the oxygen isotope composition shows 18o values in the range of 3 7 to 3 9 and is enriched in 18o by approximately 3 in comparison with co existing high mg calcite the negative 13c values suggest that the dolomite has derived its carbon via methane oxidation the genetic connection between dolomite cement formation and methane oxidation is visually supported by gas seeps from the seabed and vents in the sandstone pillars themselves it is believed that the methane originates from shallow gas in late quaternary marine deposits which led to a discharge of methane in the diagenetic zones of the topmost sedimentary column the dolomite precipitation most probably took place as a result of anaerobic methane oxidation subsequently the lithified sandstone pillars were exposed on the seafloor by large scale submarine erosion

a comparative analysis of compositional variations in and between marine ferromanganese nodules and crusts in the south pacific and their environmental controls abstract regional variation of mn fe co ni and cu in ferromanganese oxides nodules and crusts in the central south pacific is related to primary productivity oxygen minimum layer and calcium carbonate compensation depth the largely latitudinal influence of these environmental parameters on nodule and crust composition reflects their predominantly latitudinal variation primary productivity is the principal regional environmental control influencing diagenetic enrichment of these elements in nodules through its effect mediated by the ccd on supply and concentration of labile organic matter vs carbonate remains to the sediments it influences hydrogenetic enrichment of these elements in nodules and crusts through its effect mediated by the oxygen minimum layer mainly in the case of crusts on their export from surface waters the elements varying susceptibility to being scavenged or organically bound influences the contrasting composition of diagenetic vs hydrogenetic ferromanganese oxides which is further influenced by depth hydrogenesis is the fundamental process governing nodule and crust formation superimposed on which is diagenesis under specific circumstances both are subject to intermittent interruption diminution and augmentation by changes in environmental parameters application of regionally operative environmental controls locally explains local compositional variations and helps refine exploration criteria for economically viable nodules and crusts

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

possibly inverted polarity electrical structures in thunderstorms during steps 1 in full and partial vertical profiles of the electric field in thunderstorms during the severe thunderstorm electrification and precipitation study in 2000 we find evidence for inverted polarity electrical structures in the convective region of thunderstorms the evidence consists of polarities opposite from normal 1 in the peaks in the profile of the vertical component of the electric field ez and 2 in the vertical sequence of inferred charges in storms that possibly are inverted in polarity the lowest peak in ez inside the cloud is negative followed by a positive peak farther up near storm top the uppermost peak is negative and the uppermost inferred charge is positive the sounding data do not conclusively prove that inverted polarity thunderstorms exist but they support it if additional data corroborate that such storms do exist it will require modification of at least some aspects of our conceptual models of storm electrification

vhf lightning mapping observations of a triggered lightning flash 1 on 3 august 2010 an extensive lightning flash was triggered over langmuir laboratory in new mexico the upward positive leader propagated into the storm s midlevel negative charge region extending over a horizontal area of 13 13 km and 7 5 km altitude the storm had a normal polarity tripolar charge structure with upper positive charge over midlevel negative charge lightning mapping array lma observations were used to estimate positive leader velocities along various branches which were in the range of 1 3 104 m s 1 slower than in other studies the upward positive leader initiated at 3 4 km altitude but was mapped only above 4 0 km altitude after the onset of retrograde negative breakdown indicating a change in leader propagation and vhf emissions the observations suggest that both positive and negative breakdown produce vhf emissions that can be located by time of arrival systems and that not all vhf emissions occurring along positive leader channels are associated with retrograde negative breakdown

formation of charge structures in a supercell abstract lightning mapping electric field and radar data from the 26 may 2004 supercell in central oklahoma are used to examine the storm s charge structure an initial arc shaped maximum in lightning activity on the right flank of the storm s bounded weak echo region was composed of an elevated normal polarity tripole in the region of precipitation lofted above the storm s weak echo region later in the storm two charge structures were associated with precipitation that reached the ground to the left of the weak echo region six charge regions were inferred with positive charge carried on hail at the bottom of the stack farther forward in the storm s precipitation region four charge regions were inferred with negative charge at the bottom of the stack there were different charge structures in adjacent regions of the storm at the same time and regions of opposite polarity charge were horizontally adjacent at the same altitude flashes occasionally lowered positive charge to ground from the forwa

resources of the sea floor in his perspective rona reviews recent advances in knowledge of sea floor resources knowledge is expanding from those minerals eroded from land metals gemstones sand and gravel to those minerals concentrated by plate tectonic processes in ocean basins exploration of the oceans is at an early stage and development of marine mining is subject to economic and environmental considerations

geochemistry and origin of ferromanganese concretions in the gulf of bothnia abstract ferromanganese concretions cover large areas of the gulf of bothnia they are flat to well rounded the rounded ones being richer in oxyhydroxides of iron and manganese rounded and ellipsoidal nodules particularly those in the northern gulf of bothnia are richest in mn ni ba and cu which probably coexist in a mn oxyhydroxide phase flat nodules are enriched in fe p rare earths and as probably associated with an fe oxy hydroxide component aluminum v cr and ti occur in still another phase the sediments of the gulf generally consist of a 10 50 mm thick layer of oxidized surface sediment enriched in mn ba p and ni lying on top of reduced sediments which are diagenetically depleted in these elements the remobilized elements have redeposited in the nodules but this process cannot explain the origin of all the nodular material some released mn ba and ni furthermore enter into suspended phases which eventually leave the baltic sea the economic value of the nodules in the gulf of bothnia is probably limited at present

implications structurales et paleogeographiques de la presence de messinien a l ouest de gibraltar structural and paleogeographical implications of the existence of messinian layers west of gibraltar abstract a core sampled west of gibraltar shows at its base lower messinian sediments typical of the mediterranean area and at its top pleistocene sediments of atlantic type these observations lead us to consider the existence of a basin west of gibraltar which would have been isolated from the atlantic during the upper miocene though still communicating with the mediterranean through a south rifan strait the isolation of this basin during the messinian would be the result of the creation of a south iberian spur made up of the series folded during miocene events between the moroccan and iberian margins at about 9 w

hydrothermal manganese oxide deposits from baby bare seamount in the northeast pacific ocean abstract manganese oxide crusts were recovered from baby bare seamount in order to investigate the history of off axis hydrothermal venting baby bare is a small basement high protruding from a regional sediment cover on the eastern flank of the juan de fuca ridge that acts as a focus for discharging crustal fluids stratabound mn oxide crusts were collected where warm venting has been observed near the seamount summit mn oxide crusts are composed primarily of 10 a manganate pyrolusite with minor nontronite saponite and or barite these assemblage and chemical characteristics such as high mn fe ratios and low trace metal and ree concentrations are indicative of a hydrothermal origin minimum ages for these deposits calculated using growth rates 324 to 1800 mm ma and estimated thicknesses of manganese outcrops show that baby bare has been hydrothermally active for at least 0 5 myr and possibly since its formation 1 7 2 7 ma hydrothermal manganese oxide crusts such as these from baby bare record interactions between the hydrothermal fluids and seawater and are important tools for estimating the longevity of off axis hydrothermal activity

evolving complex electrical structures of the steps 25 june 2000 multicell storm abstract data from a three dimensional lightning mapping array lma and from two soundings by balloon borne electric field meters efms were used to analyze the electrical structures of a multicell storm observed on 25 june 2000 during the severe thunderstorm electrification and precipitation study steps this storm had a complex multicell structure with four sections each of whose electrical structure differed from that of the others during all or part of the analyzed period the number of vertically stacked charge regions in any given section of the storm ranged from two to six the most complex charge and lightning structures occurred in regions with the highest reflectivity values and the deepest reflectivity cores intracloud flashes tended to concentrate in areas with large radar reflectivity values though some propagated across more than one core of high reflectivity or into the low reflectivity anvil intracloud lightning flash rates decreased as the vertical extent and maximum value of ref

the chemistry of mediterranean outflow and its interactions with surrounding waters abstract the spreading of the mediterranean water mw and its interactions with the surrounding waters are described and discussed in terms of oxygen and nutrient patterns in the gulf of cadiz and off the southern portuguese coast in winter of 1998 low concentrations of nutrients and relatively constant levels of dissolved oxygen by comparison with those of the surrounding waters were associated with the warm and saline mw outflow three cores of the mw have been identified the deeper core presenting higher nutrients and lower dissolved oxygen concentrations than the upper two cores closer to the strait of gibraltar the mw remained pressed against the continental slope while to the west the cores spread horizontally offshore at the deeper mw layers some irregularities were noticed in the nutrient fields apparently associated with the complex topography of the portimao canyon the north atlantic central water nacw and the north atlantic deep water nadw were chemically identified in the area a water mass displaying a well defined minimum of o 2 157 mol kg 1 and high concentrations of nutrients have been detected entrained approximately from 750 to 1000 m depth and lying between the two main mw cores inshore and overlying the lower core of mw offshore it is suggested that this water mass is a remnant of the antarctic intermediate water aaiw

electrical structure and updraft speeds in thunderstorms over the southern great plains we have acquired 11 balloon soundings of the electric field and thermodynamics in large and sometimes severe and tornadic thunderstorms over the southern great plains the ascent rates of the balloons were used to divide the soundings into weak and strong updrafts all 11 soundings had magnitudes of charge densities and thicknesses of charge regions similar to those reported previously in small thunderstorms the five weak updraft soundings had complex charge structures of 7 9 charge regions below 10 km altitude the magnitude of the maximum measured electric field in these soundings was 100 150 k v m 1 the four soundings in strong updrafts had balloon ascent rates of at least 15 m s 1 for at least 1 km these soundings had simpler electrical structures of 3 5 charge regions below 10 km altitude their maximum measured electric fields ranged from 85 to 130 kv m 1 the data may support an earlier hypothesis that charge is elevated in strong updrafts in addition the data may suggest that simpler charge structures are associated with proximity to strong updrafts rather than with different storm types

the contourite depositional system of the gulf of cadiz a sedimentary model related to the bottom current activity of the mediterranean outflow water and its interaction with the continental margin the present paper is mostly a synthesis of work conducted on the continental margin of the gulf of cadiz using a broad database collected by several cruises and projects supported by the spanish research council and the nrl and naval oceanographic office usa including bathymetry sidescan sonar imagery seismic profiles sediment cores submarine photographs and physical oceanographic data these data have enabled us to establish a detailed understanding of the morphologic development of the margin its pliocene and quaternary stratigraphy and a full characterization of the contourite depositional system cds generated by the mediterranean outflow water mow the northern margin of the gulf of cadiz shows the following distinct features a an active compressive framework where the cadiz allocthonous unit provides an unstable substratum for late miocene pliocene and quaternary sedimentation b a relative lack of submarine canyons except in the western area of the algarve margin c a very broad continental slope that lacks a marked continental rise d a middle slope dominated by along slope processes driven by the mow which has generated a complex cds during the pliocene and quaternary and e an irregular lower slope and abyssal plain region dominated by down slope processes that is partly detached from an upper slope source region the cds is composed of both depositional and erosive features the main depositional features are characterised by sedimentary wave fields sedimentary lobes mixed drifts plastered drifts elongated mounded and separated drifts and sheeted drifts the main erosive features are contourite channels furrows marginal valleys and moats these various depositional and erosive features have a specific location along the margin and their detailed distribution is essential to understand the present and past interaction of the mow with the middle slope based on this distribution five morphosedimentary sectors have been identified within the cds which from east to west are 1 proximal scour and sand ribbons 2 overflow sedimentary lobe 3 channels and ridges 4 active contourite drifts and 5 submarine canyons the development of the cds has been controlled in general by the pliocene and quaternary environmental and paleoceanographic changes and by the morphology of the margin but in detail the development of each of these sectors is related to systematic deceleration of the mow as it flows westwards to the interaction with the margin bathymetry and to the effects of coriolis force our comprehensive sedimentary model for the cds defines the gulf of cadiz margin as a mixed contourite turbidite system with a detached combined drift fan morphology this is different from many other contourite influenced margins where the contourite processes are dominant on the middle slope and separated from the down slope processes which are characteristic on the lower slope and abyssal plains

hydrocarbon derived ferromanganese nodules in carbonate mud mounds from the gulf of cadiz mud breccia sediments and clasts as nucleation sites abstract more than 500 fe mn nodules were sampled during the anastasya 01 cruise tasyo project along the continental margin of the gulf of cadiz eastern central atlantic at the confluence of the mediterranean sea with the atlantic ocean where extensive nodule fields were discovered based on wide previous studies that included swath bathymetry multi channel and very high resolution seismic reflection gravimetry magnetism and underwater photography surveys nodules were collected at water depths ranging from 850 to 1000 m associated with hydrocarbon derived ankerite and dolomite chimneys and crusts thirty six selected samples among the various morphological types were used for the laboratory analysis of physical properties morphology colour surface texture sphericity weight and size mineralogy xrd optical and electronic microscopy and geochemistry xrf aas icp ms epma gc ms s c and o isotopes nodules show a wide range of sizes densities weights and morphologies nodules are formed of multiple millimetre thick layers of fe and mn oxyhydroxides surrounding the nucleus composed of early middle miocene plastic marl the textures developed by the fe and mn oxyhydroxides layers are massive laminated detrital and mottled to dendritic goethite lepidocrocite mn oxides 7 a manganates and 10 a manganates quartz and phyllosilicates are the main components accessory minerals are calcite dolomite siderite rhodochrosite kutnohorite pyrite chalcopyrite potassium feldspar zircon rutile ilmenite and chlorite fe mn carbonates from the siderite rhodochrosite continuous series are forming part of the marl nuclei framboidal filamentous and globular textures are observed in fe mn oxides and pyrite suggesting biogenic origin nodules show a high mean abundance of fe 38 6 moderate mn 6 0 and low contents of trace metals and rees compared to the average content of deep seabed polymetallic nodules from other oceanic areas the mn fe ratio ranges from 0 07 to 0 25 the studied nodules hold in their oxide layers hydrocarbons n alkanes derived from marine bacterial activity aromatic hydrocarbons in the form of phenanthrene are also present which is characteristic of mature petroleum the structure mineralogy and chemical composition in the studied nodules are similar to those of diagenetic hydrogenetic continental margin nodules rather than deep sea nodules we suggest that the formation of this type of nodule occurred through a combined diagenetic hydrogenetic growth process involving fluid venting from deep seated hydrocarbon reservoirs bio mineralization processes and bottom current erosion

cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the pacific sea floor ferromanganese oxide crusts which accumulate on unsedimented surfaces in the open ocean1 6 derive most of their metal content from dissolved and particulate matter in ambient bottom water7 8 in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions9 they differ in this respect from abyssal nodules much of whose metals are remobilized from host sediments here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the pacific ocean we propose that depletion of cobalt in pacific crusts measures the location and intensity of submarine hydrothermal discharge use of the cobalt chronometer an algorithm inversely relating cobalt content and crust growth rate permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity based dating methods these maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the central pacific ocean cobalt enriched crusts are found where water masses are most isolated from continental coastal and hydrothermal sources of metals now and in the past this relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms

lightning location relative to storm structure in a supercell storm and a multicell storm relationships between lightning location and storm structure are examined for one radar volume scan in each of two mature severe storms one of these storms had characteristics of a supercell storm and the other was a multicell storm data were analyzed from dual doppler radar and dual vhf lightning mapping systems the distributions of vhf impulse sources were compared with radar reflectivity vertical air velocity and their respective gradients in the supercell storm lightning tended to occur along streamlines above and downshear of the updraft and reflectivity cores vhf impulse sources were most concentrated in reflectivities between 30 and 40 dbz and were distributed uniformly with respect to updraft speed in the multicell storm on the other hand lightning tended to coincide with the vertical reflectivity and updraft core and with the diverging streamlines near the top of the storm the results suggest to us that the location of lightning in these severe storms was most directly associated with the wind field structure relative to updraft and reflectivity cores since the magnitude and vertical shear of the environmental wind are fundamental in determining the reflectivity and wind field structure of a storm we suggest that these environmental parameters are also fundamental in determining lightning location

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

trace elements in native gold by solution icp ms and their use in mineral exploration a british columbia example abstract an elegantly simple aqua regia based icp ms analytical procedure is used to compare the trace element composition of density separated alluvial native au from seven stream silt samples with three samples of geographically associated au from a prospective ore deposit in central british columbia not all of the alluvial au could have come from the ore deposit based on present drainage the silt sample au averaging four alluvial grains and totaling 12 250 g per sample generally yielded measurable concentrations for v fe cu as pd ag sb pt and bi the bedrock au samples represent the three dominant rock types in the showing their au trace element compositions largely bracket the alluvial au multidimensional scaling exploratory statistics shows that trace elements in the native au form lithophile chalcophile and siderophile groupings this indicates that a small set of geochemical processes formed all the au in one geologic environment previous work shows that au from individual deposits has distinct assemblages of detectable elements given these observations and that detectable elements are the same in both the deposit and alluvial au and that concentrations in the former bracket those of the latter it is concluded that the source of the alluvial au has probably been identified apparently neither mineral inclusions nor weathering impaired fingerprinting of the au the simplicity of the approach indicates that this is a useful exploration tool for determining the bedrock source of alluvial au the study also shows that silt sample exploration in glaciated terrains must recognize that paleo ice movement and paleo stream directions can yield geographic distributions of alluvial au that cannot be explained by present day drainage patterns thus this simple analytical exploration technique is potentially very useful to the exploration industry

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

bacterially mediated diagenetic origin for chert hosted manganese deposits in the franciscan complex california coast ranges numerous manganese deposits in the franciscan complex california occur as conformable lenses within bedded radiolarian chert argillite sequences that are in turn intercalated within thicker sections of sandstone and shale the field relations composition and petro graphic and isotopic characteristics indicate that the manganese was concentrated by diagenetic reconstitution of siliceous and hemipelagic sediment during burial the ore lenses are mn rich and fe poor assemblages consisting largely of rhodochrosite manganese silicates opal ct disordered cristobalite tridymite and quartz highly negative 13 c values for the carbonate carbon in rhodochrosite indicate that co 2 likely originated from oxidation of methane less negative values result from mixing of methanogenic carbon and co 2 derived from bacterial degradation of organic matter the 18 o values for the carbonate of rhodochrosite indicate temperatures of formation between 12 and 100 c the oxidation of methane prior to carbonate precipitation may have used the minor 0 4 0 5 mn and fe oxyhydroxides and oxides deposited with the sediment the mobilization of manganese from biogenic and terrigenous sources in the sediment column into discrete horizons and the fractioriation of manganese from iron reflect the presence of oxidation reduction boundaries and gradients in the sediment column fluids derived from compaction and silica dehydration reactions in the transformation of opal a x ray amorphous biogenic silica to quartz were involved in transportation of principal components sedimentary and geochemical attributes suggest that the deposits formed in a deep water environment in a zone of oceanic upwelling near a continental margin

evolution of lightning activity and storm charge relative to dual doppler analysis of a high precipitation supercell storm abstracta high precipitation tornadic supercell storm was observed on 29 30 may 2004 during the thunderstorm electrification and lightning experiment observational systems included the oklahoma lightning mapping array mobile balloon borne soundings and two mobile c band radars the spatial distribution and evolution of lightning are related to storm kinematics and microphysics specifically through regions of microphysical charging and the location and geometry of those charge regions lightning flashes near the core of this storm were extraordinarily frequent but tended to be of shorter duration and smaller horizontal extent than typical flashes elsewhere this is hypothesized to be due to the charge being in many small pockets with opposite polarities of charge close together in adjoining pockets thus each polarity of lightning leader could propagate only a relatively short distance before reaching regions of unfavorable electric potential in the anvil however lightning extended tens of kilome

hydrothermal oxide and nontronite deposits on seamounts in the eastern pacific deposits of fe oxide mud nontronite and fe mn crusts were sampled from the summits of two seamounts in the eastern pacific where low temperature 0 15 c hydrothermal fluids are issuing the deposits consist of x ray amorphous fe oxyhydroxide and are rich in fe 43 wt contain minor si and p 4 and 3 5 respectively and have very low mn 0 01 and other trace element contents other deposits where no current hydrothermal activity was observed consist of mud and crusts composed of amorphous material and poorly crystalline hematite goethite and smectite these deposits have slightly higher mn up to 2 and other trace element contents the mineralogical and chemical differences between the active and inactive deposits and crusts are interpreted to be due to recrystallization and contamination with detrital biogenic hydrogenous and possibly hydrothermal sulfide material nontronite deposits capped by fe mn oxides were sampled from one of the seamounts these deposits have compositions similar to other seafloor nontronite deposits and formed at low temperatures 30 c during mixing of low temperature hydrothermal fluids with seawater the oxide deposits consist almost entirely of long delicate filaments remarkably similar in morphology to genera of fe oxidizing bacteria such bacteria were probably important in catalyzing the oxidation and precipitation of iron from hydrothermal fluids on the seamounts the occurrence of nearly identical filament rich oxide deposits on two widely separated seamounts suggests that this type of deposit may be common on seamounts but previously unrecognized