authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

the relationship between sedimentary facies and faunal associations in the llandovery siliciclastic ross brook formation arisaig nova scotia the llandovery siliciclastic ross brook formation of arisaig nova scotia comprises three broadly defined sedimentary facies these are a mottled silty mudstone facies facies a a laminated shale facies facies b and a laminated siltstone facies facies c facies a consists of variably bioturbated silty mudstones muddy siltstones and fissile shales it developed in relatively shallow water conditions mudstones were presumably deposited from suspension and siltstone laminae and thin layers were formed by increased wave and current activity mottling resulted from bioturbation by epifaunal and particularly infaunal benthic organisms within facies a two subfacies are recognized a i is mudstone dominated and a ii is fine grained siltstone dominated facies b consists of alternating laminae of undisturbed mudstone and fine grained siltstone probably produced as a result of deposition from suspension during a temporary upward expansion of the oxygen minimum layer facies c consists of 0 5 30 c

late cretaceous and early paleogene nutrient and paleoproductivity records from blake nose western north atlantic ocean 1 we evaluate phosphorus p and biogenic barium bio ba as nutrient burial and export productivity indicators for the late cretaceous and early paleogene combining these with calcium carbonate caco3 organic carbon c and bulk caco3 c isotopes 13c sample ages span 36 71 ma 1 sample 0 5 m y for a depth transect of sites in the western north atlantic blake nose ocean drilling program leg 171b sites 1052 1051 and 1050 we use a multitracer approach including redox conditions to investigate export productivity surrounding the global paleocene 13c maximum 57 ma reducing conditions render most of the bio ba record not useful for export productivity interpretations p and organic c records indicate that regional nutrient and organic c burial were high at 61 and 69 ma and low during the paleocene 13c maximum a time of proposed global high relative organic c burial observed organic c burial changes at blake nose cannot explain this c isotope excursion

remobilization of authigenic uranium in marine sediments by bioturbation uranium behaves as a nearly conservative element in oxygenated seawater but it is precipitated under chemically reducing conditions that occur in sediments underlying low oxygen bottom water or in sediments receiving high fluxes of particulate organic carbon sites characterized by a range of bottom water oxygen bwo and organic carbon flux ocf were studied to better understand the conditions that determine formation and preservation of authigenic u in marine sediments our study areas are located in the mid latitudes of the northeast pacific and the northwest atlantic oceans and all sites receive moderate 0 5 g cm2 kyr to high 2 8 g cm2 kyr ocf to the sediments bwo concentrations vary substantially among the sites ranging from 3 to 270 m a mass balance approach was used to evaluate authigenic u remobilization at each site within each region studied the supply of particulate nonlithogenic u associated with sinking particles was evaluated by means of sediment traps the diffusive flux of u into sediments was calculated from pore water u concentration profiles these combined sources were compared with the burial rate of authigenic u to assess the efficiency of its preservation a large fraction one third to two thirds of the authigenic u precipitated in these sediments via diffusion supply is later regenerated even under very low bwo concentrations 15 m bioturbating organisms periodically mix authigenic u containing sediment upward toward the sediment water interface where more oxidizing conditions lead to the remobilization of authigenic u and its loss to bottom waters

a model for a seismic computerized alert network in large earthquakes damaging ground motions may occur at large epicentral distances because of the relatively slow speed of seismic waves it is possible to construct a system to provide short term warning as much as several tens of seconds of imminent strong ground motions from major earthquakes automated safety responses could be triggered by users after receiving estimates of the arrival time and strength of shaking expected at an individual site although warning times are likely to be short for areas greatly damaged by relatively numerous earthquakes of moderate size large areas that experience very strong shaking during great earthquakes would receive longer warning times

control of manganese and iron in skagerrak sediments northeastern north sea three cores with variable physicochemical characteristics from different areas of the skagerrak northeastern north sea have been studied to understand the processes such as redox conditions caco3 bioturbation etc controlling the fe and mn abundance in sediments sequential extraction was performed to identify the partitioning patterns of these elements into sorbed and carbonate mn fe oxyhydroxide fe oxyhydroxide residual leachable and residual non leachable phases pore water fe and mn contents in the central skagerrak increase up to 100 mm depth while they reach maximum concentrations around 50 mm depth in the southern skagerrak sediments the fe redox boundary lies below the mn redox boundary whereas the latter coincides with the level of oxygen penetration extractable mn in the upper layers of the central basin sediments is 10 times higher than that present in sediments of the southern part 30 mmol kg 1 fe is present in all fractions extracted but mn occurs mainly in carbonate and fe mn oxyhydroxide phases total extractable fe is about three times less than that of total fe in all cores whereas total mn is nearly equivalent to the total extractable mn mn in sediments showed two peaks the surficial one due to precipitation of oxyhydroxides from the diagenetically upwelled and sedimented mn from overlying waters and the deeper one associated with diagenetically formed carbonate phase the substitution approach has been used to explain the presence of significant quantities of mn and fe in the carbonate phase the computed observed partition coefficients decrease with depth in general but increase with corresponding decrease in ca substantiating the ionic replacement reactions mn in the carbonate phase is negatively related to caco3 suggesting possible rhodochrosite formation evaluated observed and thermodynamic partition coefficients revealed the likelihood of siderite formation solutions to diagenetic equations showed contrasting behaviour of mn and fe in skagerrak sediments increased reduction of mn oxyhydroxides in the central parts compared to that in the southern skagerrak results in the significant enrichment rate of mn in pore water 1365 mol m 3 yr 1 in sediments of the former area large amounts of fe oxyhydroxides are reduced in southern parts compared to the skagerrak basin itself mn and fe fluxes from reducing to oxidizing zones are larger in the southern skagerrak 8 8 and 9 0 m mol m 2 yr 1 respectively than in central parts 5 3 and 4 6 m mol m 2 yr 1 respectively mn and fe also exhibit contradicting sedimentation patterns where the former has high deposition fluxes in the central skagerrak while the latter is deposited more in the southern skagerrak mn seems to be internally cycled within the skagerrak

evidence for basin restriction during syn collisional basin formation in the silurian arisaig group nova scotia the arisaig basin in nova scotia canada provides a regional sedimentary record of an early silurian basin subsidence on the microcontinent of avalon the lower members of the arisaig group beechill cove and lower ross brook formations are likely to be deposited in a basin formed during syn to post collisional rifting subsidence driven by the collision of avalon and baltica the evolution of this constricted basin can be tracked by examining the geochemistry of the sedimentary rocks deposited within the basin here we report on the chemostratigraphy of the arisaig group a series of siliciclastics with a focus on understanding the redox chemistry during sedimentation the trace and major element geochemistry of this group provides insight into the oceanographic and geological processes that were influencing its depositional environment in particular concentrations of u v mo ni cd and pb indicate regional shifts in ocean redox state which serve as a proxy for changes in ocean circulation and regional tectonic activity we find evidence for anoxic conditions near the base of ross brook formation and attribute this anomaly in redox status to a significant change in physical mixing in the region trace element concentrations indicate that this anoxic event was associated with poor circulation rather than elevated productivity and organic matter burial based on these data we confirm that these sediments are deposited in a tectonically formed basin during a period of limited ocean circulation

a modern vs permian black shale the hydrography primary productivity and water column chemistry of deposition the sediment currently accumulating in the cariaco basin on the continental shelf of venezuela has an elevated organic carbon content of approximately 5 is accumulating under o2 depleted bottom water conditions so42 reduction is composed dominantly of foraminiferal calcite diatomaceous silica clay and silt and is dark greenish gray in color upon lithification it will become a black shale recent studies have established the hydrography of the basin and the level of primary productivity and bottom water redox conditions these properties are used to model accumulation rates of cd cr cu mo ni v and zn on the seafloor the model rates agree closely with measured rates for the uppermost surface sediment the model is applied to the meade peak phosphatic shale member of the phosphoria formation a phosphate deposit of permian age in the northwest united states it too has all of the requisite properties of a black shale although the deposit is a world class phosphorite it is composed mostly of phosphatic mudstone and siltstone chert limestone and dolomite it has organic carbon concentrations of up to 15 is strongly enriched in several trace elements above a terrigenous contribution and is black the trace element accumulation defines a mean primary productivity in the photic zone of the phosphoria basin as moderate at 500 g m 2 year 1 organic carbon comparable to primary productivity in the cariaco basin the source of nutrient enriched water that was imported into the phosphoria basin upwelled into the photic zone and supported primary productivity was an o2 minimum zone of the open ocean the depth range over which the water was imported would have been between approximately 100 and 600 m the mean residence time of bottom water in the basin was approximately 4 years vs 100 years in the cariaco basin the bottom water was o2 depleted but it was denitrifying or no3 reducing rather than so42 reducing

a new method of quickly estimating epicentral distance and magnitude from a single seismic record rapid estimation of the epicentral distance and magnitude is of fundamental importance for early earthquake detection and warning systems we present a novel method of estimating the epicentral distance from a single seismic record in a short amount of time in order to quantitatively evaluate the difference in observed seismic waveforms we introduced a simple function with the form of bt exp at and determined a and b in terms of the least squares method by fitting this function to the initial part of the waveform envelope we have found that log b is inversely proportional to log where is the epicentral distance this relation holds true regardless of the earthquake magnitude by using this relation we can roughly estimate the epicentral distance nearly immediately after the p wave arrival then we can readily estimate the magnitude from the maximum amplitude observed within a given short time interval after the p wave arrival by using an empirical magnitude amplitude relation that includes the epicentral distance as a parameter manuscript received 11 january 2002

reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments abstract sporadic direct observations over a 50 yr period inadequately characterize the history of seasonal hypoxia and anoxia in chesapeake bay a large estuary threatened by eutrophication here we undertake a reconstruction of 20th century oxygen depletion in this estuary using mo concentrations in 210pb dated sediments cu concentrations are used to control for anthropogenic influences cores from the central channel display mild mo enrichments above crustal backgrounds up to 5 g g and strong cu enrichments up to 35 g g temporally cu enrichment mostly anthropogenic began earlier and stabilized in the last two thirds of the 20th century in contrast mo enrichment has grown during the last two thirds of the century molybdenum enrichment is mostly hydrogenic except in a section of the channel that receives additional mo from erosion of early miocene shore deposits two geochemical mechanisms promote mo enrichment manganese refluxing concentrates dissolved moo42 at the sediment water interface and sulfide substitution into moo42 produces thiomolybdates which can be fixed by particles the mo enrichment mechanisms operate primarily during periods when bottom waters are anoxic and thiomolybdate formation can occur near the sediment water interface this implies a temporal coupling between water column anoxia and mo fixation even though fixation occurs only within sediments the mo enrichment profiles suggest that chesapeake bay has experienced growing o2 depletion since the first half of the 20th century but especially after 1960

magnitude determination using initial p waves a single station approach 1 prompted by recent success in the research and application of earthquake early warning systems we conducted an investigation into the relationship between the magnitudes of earthquakes and the properties of the first three seconds of the p waves at a single station using waveforms at station nacb of the broadband array in taiwan for seismology from 46 earthquakes within 100 km epicentral distance we found a linear correlation between the magnitudes and the logarithmic characteristic periods of the initial p waves for earthquakes up to magnitude 6 5 we also detected a deterministic relationship between the magnitudes and the peak amplitudes of the initial p waves for earthquakes of magnitude m 6 5 while further study needs to be done on the behavior of the initial p wave peak amplitudes from larger earthquakes we propose here that the characteristic periods and peak amplitudes of the first three seconds of the p waves be used jointly in onsite single station earthquake early warning operations

occurrence and significance of silurian k bentonite beds at arisaig nova scotia eastern canada the most extensive succession of k bentonite beds known in the silurian of north america occurs at arisaig on the northern coast of nova scotia at least 40 ash beds are present in the llandoverian

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

carbon and nitrogen isotope excursions in mid pleistocene sapropels from the tyrrhenian basin evidence for climate induced increases in microbial primary production the modern mediterranean sea is oligotrophic yet its sediment record contains layers of organic carbon rich sapropels at 21 ky precessional spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important we have made a high resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3 m sequence that corresponds to 1001 to 946 ka organic 13c values systematically increase from 26 to 21 and 15n values systematically decrease from 4 to 0 as organic carbon mass accumulation rates increase in the sapropel layers the increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates the decrease in nitrogen isotope values implies major contributions of nitrogen fixing cyanobacteria to the total marine productivity the precessional minima with which sapropels coincide were times of wetter climate that stratified the surface mediterranean sea increased delivery of soil derived phosphorus and evidently amplified microbial primary production our high resolution study reveals several relatively rapid excursions into and out of the high productivity mode that suggest that sapropel deposition was a climate sensitive surface driven phenomenon that was not accompanied by basin wide stagnation

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

statistical analysis of strong motion accelerograms and its application to earthquake early warning systems summary in view of increasing damage due to earthquakes and the current problems of earthquake prediction real time warning of strong ground motion is attracting more interest in principle it allows short term warning of earthquakes while they are occurring with warning times of up to tens of seconds it is possible to send alerts to potential areas of strong shaking before the arrival of the seismic waves and to mitigate the damage but only if the seismic source parameters are determined rapidly the major problem of an early warning system is the real time estimation of the earthquake s size we investigated digitized strong motion accelerograms from 244 earthquakes that occurred in north and central america between 1940 and 1986 to find out whether their initial portions reflected the size of the ongoing earthquake applying conventional methods of time series analyses we calculate appropriate signal parameters and describe their uncertainties in relation to the magnitude and epicentral distance the study reveals that the magnitude of an earthquake can be predicted from the first second of a single accelerogram within f 1 36 magnitude units the uncertainty can be reduced to about f0 5 magnitude units if a larger number 2 8 of accelerograms are available which requires a dense network of seismic stations in areas of high seismic risk

a prototype earthquake warning system for strike slip earthquakes a prototype expert system has been developed to provide rapid warning of earthquakes while they are occurring warning times of up to 100 seconds will be possible in the complete system several accelerometers are distributed at intervals within a few kilometers of a known fault data are telemetered to a central computer which implements the expert system the expert system incorporates specific information about the type of fault to be monitored and includes simple rules for estimating the fault slip rupture length and seismic moment all in real time if the seismic moment exceeds a preset value an alarm may be issued the prototype is designed for deployment on near surface strike slip faults such as the san andreas and has been successfully tested with data from the 1979 imperial valley and 1984 morgan hill earthquakes crucial concepts have also been tested using synthetic data calculated for a model of the 1857 fort tejon earthquake parkfield california could be used as a test site

quick and reliable determination of magnitude for seismic early warning this article reports efforts toward using real time earthquake monitoring by the taiwan central weather bureau to meet the needs of seismic early warning twenty three sets of strong motion data from moderate earthquakes m 5 0 in the taiwan area are used to demonstrate the feasibility of this goal for earthquakes larger than ml 5 epicenters can be reliably determined in about 15 sec after the arrival of the p wave at the nearest station the earthquake magnitude m l cannot be determined in the same time frame due to incomplete recording of shear waves at some stations however the magnitude based on the first 10 sec of signal ml10 can be related to ml as follows ml 1 28 ml10 0 85 0 13 our results show that the real time strong motion system routinely used by the cen tral weather bureau can be used to determine epicenters and magnitudes in about 30 sec after occurrence of earthquakes in taiwan such information hopefully can be used to reduce damage to society

magnitude period scaling relations for japan and the pacific northwest implications for earthquake early warning scaling relations between the predominant period of p wave arrivals and earthquake magnitude are explored using datasets from the pacific northwest and japan and compared with previous observations in southern california allen and kanamori 2003 we find the same scaling for events in all three geologically diverse regions the sensitivity of the predominant period observation to magnitude can be optimized using various frequency bands for different magnitude ranges and in dif ferent regions the ability to estimate the magnitude using the first few seconds of the p wave offers a methodology for earthquake early warning the accuracy of magnitude estimates increases with the number of stations reporting predominant period observations the most significant improvements in the magnitude estimate occur when the number of reporting stations increased from one to four as in south ern california we find that the average absolute magnitude error is 0 5 magnitude units when the closest four stations to the epicenter are used

early warning system for aftershocks a prototype early warning system to provide san francisco and oakland california a few tens of seconds warning of incoming strong ground shaking from already occurred m 3 7 aftershocks of the magnitude 7 1 17 october 1989 loma prieta earthquake was operational on 28 october 1989 the prototype system consisted of four components ground motion sensors in the epicentral area a central receiver a radio repeater and radio receivers one of the radio receivers was deployed at the california department of transportation caltrans headquarters at the damaged cypress street section of the i 880 freeway in oakland california on 28 october 1989 and provided about 20 sec of warning before shaking from the m 4 5 loma prieta aftershock that occurred on 2 november 1989 at 0550 utc in its first 6 months of operation the system generated triggers for all 12 m 3 7 aftershocks for which trigger documentation is preserved did not trigger on any m 3 6 aftershocks and produced one false trigger as a result of a now corrected single point of failure design flaw because the prototype system demonstrated that potentially useful warnings of strong shaking from aftershocks are feasible the usgs has completed a portable early warning system for aftershocks that can be deployed anywhere

tectonic significance of a llanvirn age for the dunn point volcanic rocks avalon terrane nova scotia canada implications for the evolution of the iapetus and rheic oceans abstract the paleozoic evolution of avalonia is crucial to the understanding of the development of the appalachian orogen and the iapetus and rheic oceans paleomagnetic faunal structural and isotopic data indicate that avalonia had accreted to laurentia by the early silurian in the avalon terrane of nova scotia ordovician early devonian rocks consist of bimodal volcanic rocks at the base dunn point formation disconformably overlain by a thick sequence of fossiliferous siliciclastics arisaig group which contain llandoverian to lochkovian fossils until now the only published age data for the volcanic rocks yielded an imprecise rb sr whole rock isochron age of 421 15 ma and the volcanism has been interpreted to reflect local extension and basin development related to the oblique collision between avalonia and laurentia after closure of the iapetus ocean we present u pb zircon data from a rhyolite which indicate an age of 460 0 3 4 ma for the dunn point formation an age that requires a re interpretation of its tectonic setting the dunn point volcanism probably developed on the avalonian microcontinent outboard from both laurentia and gondwana possibly in a rifted arc setting analogous to the modern taupo zone in northern new zealand a llanvirn age for these felsic rocks also reconciles apparently conflicting paleomagnetic data and inferred paleolatitude for avalonia in the ordovician silurian and implies 10 northward movement of avalonia between 460 and 440 ma and about 5 5 cm year for the latitudinal component of the convergence between avalonia and laurentia i e the destruction of the iapetus ocean and divergence between gondwana and avalonia development of the rheic ocean during this interval