marine 187os 188os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during oceanic anoxic event 2 high resolution osmium os isotope stratigraphy across the cenomanian turonian boundary interval from 6 sections for four transcontinental settings has produced a record of seawater chemistry that demonstrates regional variability as a function of terrestrial and hydrothermal inputs revealing the impact of palaeoenvironmental processes in every section the 187os 188os profiles show a comparable trend radiogenic values in the lead up to oceanic anoxic event 2 oae 2 an abrupt unradiogenic trend at the onset of oae 2 an unradiogenic interval during the first part of oae 2 and a return to radiogenic values towards the end of the event above the cenomanian turonian boundary the unradiogenic trend in 187os 188os is synchronous in all sections previous work suggests that activity of the caribbean lip large igneous province was the source of unradiogenic os across the oae 2 and possibly an instigator of anoxia in the oceans here we assess this hypothesis and consider the influence of activity from other lips such as the high arctic lip a brief shift to high radiogenic 187os 188os values occurred in the western interior seaway before the onset of oae 2 we evaluate this trend and suggest that a combination of factors collectively played critical roles in the initiation of oae 2 differential input of nutrients from continental and volcanogenic sources coupled with efficient palaeocirculation of the global ocean and epeiric seas enhanced productivity due to higher nutrient availability which permitted penecontemporaneous transport of continental and lip derived nutrients to trans equatorial basins

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

basalt seawater interaction the plenus cold event enhanced weathering and geochemical change deconstructing oceanic anoxic event 2 cenomanian turonian late cretaceous oceanic anoxic event 2 cenomanian turonian ca 94 ma represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic matter entered the marine burial record probably triggered by increased availability of nutrients for planktonic biota three sections eastbourne sussex uk raia del pedale campania italy and tarfaya morocco recording this event illustrate the influence on marine geochemistry of mafic volcanic rock seawater interaction anoxia to euxinia and re oxygenation and cooling during the so called plenus cold event the eastbourne section represents the organic lean epicontinental pelagic deposits of the english chalk the raia del pedale section represents a shallow water platform carbonate on the tethyan continental margin also largely devoid of organic matter and the tarfaya core represents an atlantic margin site where cyclically bedded organic rich sediments were well developed correlation between all three sections is readily achieved by biostratigraphy and carbon isotope stratigraphy 13ccarb and 13corg over the oceanic anoxic event 2 interval represented by a characteristic broad positive carbon isotope excursion the stratigraphic range of the plenus cold event defined by the presence in two discrete levels of boreal fauna and an excursion to heavier oxygen isotope values in the english chalk can be identified in raia del pedale and tarfaya by using the carbon isotope curve as a correlative tool similarly a section in southern france allows its co existing osmium isotope excursion to relatively unradiogenic values to be placed in the context of the oceanic anoxic event in all three analysed sections a fall to lower osmium isotope values clearly pre dated the onset of oceanic anoxic event 2 as defined by the initial rise in carbon isotope values allowing the putative magmatic mafic event as a trigger for the oceanic anoxic event an initial drop in sulphur isotope ratios 34scas at eastbourne correlates with the osmium isotope curve suggesting that isotopically light sulphur could have been derived from a mafic igneous source re oxygenation of sediments of all three investigated sections during the plenus cold event is variably illustrated by change in cerium calcium iodine calcium molybedenum calcium and uranium calcium ratios according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature changes in molybdenum isotope ratios from tarfaya and portions of the sulphur isotope curve from eastbourne and raia del pedale also indicate the probable presence of more oxygen rich bottom waters during the plenus cold event oxidation by such waters of previously deposited organic rich shales as well as loss of anoxic euxinic sinks is credited with temporarily enriching global seawater in a range of other redox sensitive trace metals for example v cr co ni cu zn and cd during ongoing basalt seawater interaction indicated by persistent relatively non radiogenic osmium isotope seawater values however early diagenetic enrichment of manganese in the english chalk over much of the oceanic anoxic event interval is broadly correlative in time with relatively low osmium isotope values in sections elsewhere a relationship that may be due to the lack of affinity of manganese with carbon rich shales hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks unlike other redox sensitive species the calcium isotope and lithium isotope ratios from eastbourne and raia del pedale indicate an increase in global weathering during the initial phase of oceanic anoxic event 2 and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more large igneous provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of oceanic anoxic event 2 caused the plenus cold event

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

geochemical characteristics of organic rich shale upper yangtze basin implications for the late ordovician early silurian orogeny in south china abstract the tectonic sedimentary environment of the upper yangtze basin in china underwent significant changes from the late ordovician to early silurian the widely distributed shale formed during this interval has recorded key information about paleo ocean conditions analysis of major trace and rare earth elements was conducted on 135 shale samples collected from five wells in the study area the covariation of the mo u enrichment factors indicates that the upper yangtze basin in the wufeng stage was characterized by sedimentary differentiation the southern basin was dominated by a reducing bottom water environment under euxinic conditions the northern and central basins were dominated by a suboxic anoxic environment up to the early longmaxi stage the upper yangtze basin formed a relatively uniform sedimentary environment with gradually increasing oxygen content in the bottom water the paleoproductivity index indicates that marine organisms flourished in the wufeng to early longmaxi stages making an important contribution to the siliceous content in organic rich shale subsequently terrestrial siliciclastics gradually dominated analysis of paleogeography rare earth elements and weathering indicates that chuanzhong and qianzhong uplifts in the wufeng stage were the provenance area of the upper yangtze basin with a relatively high weathering degree weathering decreased in the beginning of the longmaxi stage and then gradually increased with the xuefeng uplift becoming the main provenance areas after the early longmaxi stage controlled by stress transfer from the continuous syn caledonian kwangsian orogeny in eastern south china the upper yangtze basin and xiangzhong basin were squeezed and pushed up successively the uplift separated the open shallow sea and formed a relatively limited deep water shelf environment resulting in a relatively euxinic bottom water environment which was favorable for organic matter accumulation the tectonic sedimentary evolution of the upper yangtze basin in the late ordovician to early silurian proposed in this study indicates that the formation of organic enriched shale was not only related to glacio eustatic change but also strongly controlled by tectonic activities in south china

iron isotope and trace metal records of iron cycling in the proto north atlantic during the cenomanian turonian oceanic anoxic event oae 2 1 the global carbon cycle during the mid cretaceous 125 88 million years ago ma experienced numerous major perturbations linked to increased organic carbon burial under widespread possibly basin scale oxygen deficiency and episodes of euxinia anoxic and h2s containing the largest of these episodes the cenomanian turonian boundary event ca 93 5 ma or oceanic anoxic event oae 2 was marked by pervasive deposition of organic rich laminated black shales in deep waters and in some cases across continental shelves this deposition is recorded in a pronounced positive carbon isotope excursion seen ubiquitously in carbonates and organic matter enrichments of redox sensitive often bioessential trace metals including fe and mo indicate major shifts in their biogeochemical cycles under reducing conditions that may be linked to changes in primary production iron enrichments and bulk fe isotope compositions track the sources and sinks of fe in the proto north atlantic at seven localities marked by diverse depositional conditions included are an ancestral mid ocean ridge and euxinic intermittently euxinic and oxic settings across varying paleodepths throughout the basin these data yield evidence for a reactive fe shuttle that likely delivered fe from the shallow shelf to the deep ocean basin as well as 1 hydrothermal sources enhanced by accelerated seafloor spreading or emplacement of large igneous province s and 2 local scale fe remobilization within the sediment column this study the first to explore fe cycling and enrichment patterns on an ocean scale using iron isotope data demonstrates the complex processes operating on this scale that can mask simple source sink relationships the data imply that the proto north atlantic received elevated fe inputs from several sources e g hydrothermal shuttle and detrital inputs and that the redox state of the basin was not exclusively euxinic suggesting previously unknown heterogeneity in depositional conditions and biogeochemical cycling within those settings during oae 2

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

decoupling of the carbon cycle during ocean anoxic event 2 the cenomanian to turonian boundary transition ca 95 93 ma represents one of the most profound global perturbations in the carbon cycle of the past 140 m y this interval is characterized by widespread deposition of organic rich fine grained sediment marked by a globally recognized positive carbon isotope excursion cie reflecting the widespread removal of 12 c enriched organic matter in marine sediments under global anoxic greenhouse conditions however the exact timing and trigger of this inferred global phenomenon termed oceanic anoxic event 2 oae 2 is still debated with recent studies showing diachroneity between the deposition of the organic rich sediment and the cie and conflicting interpretations on detailed redox analyses in several of these inferred anoxic settings here we present the first evidence for widespread and persistent oxygenation during oae 2 based primarily on the distribution of redox sensitive trace metals and biota preserved in sedimentary rocks from the western interior seaway of north america our data indicate anoxic euxinic conditions in the mid to late cenomanian but improved bottom water oxygenation prior to and during the cie trace metal enrichments support large volumes of mafic volcanism possibly from the high arctic large igneous province halip which occur within the middle of the cie indicating that the emplacement of lips was not the primary trigger of the cenomanian turonian cie the apparent paradox of an oxygenated phase within oae 2 suggests a much more complex carbon cycle during these global perturbations than previously thought these findings have important implications for greenhouse carbon cycle changes over time scales of 0 1 10 m y

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

high resolution osmium data record three distinct pulses of magmatic activity during cretaceous oceanic anoxic event 2 oae 2 abstract oceanic anoxic event 2 oae 2 occurred at the cenomanian turonian boundary 94 1 ma and was a time of profound global changes in ocean chemistry and the carbon cycle this event was characterized by a positive carbon isotope excursion cie caused by massive organic carbon burial global greenhouse temperatures ocean deoxygenation and changes in ocean life driven by large igneous province lip activity lips throughout the phanerozoic have had dynamic magma flux with episodes of major eruptions interspersed with periods of relatively less intense eruptions a possible trigger for lip activity throughout the phanerozoic has been attributed to extraterrestrial impacts because there are multiple contemporaneous occurrences of large craters lip activity and mass extinctions in the geologic record at the cenomanian turonian boundary there is a 25 km diameter rim to rim complex crater in nw alberta canada known as the steen river impact structure dated at 91 7 ma carrigy and short 1968 an alternative explanation for those craters found contemporaneous with lip activity and mass extinctions is that they were created by large explosive events related to lip activity explosive events associated with mantle plume incubation beneath cratonic lithosphere have been suggested to create geologic features commonly attributed to impacts e g shocked quartz microspherules etc currently the trigger for lip activity during oae 2 as well as the duration of lip activity and the temporal variation and magnitude of eruption rates are not well constrained to address the issue of lip eruption rates and the trigger for lip activity we examined osmium os abundances and isotopes as well as highly siderophile element hse for this study re ru pd os ir pt abundance data from a continuous sedimentary section spanning oae 2 the section is from the eagle ford group in the iona 1 core deposited in the cretaceous western interior seaway kwis we found three high os concentration intervals with mantle like initial osi isotope initial 187os 188os values of 0 16 these intervals are interpreted to reflect high flux lip magmatic pulses between the pulses lower os abundances with more radiogenic osi values of 0 20 are observed which we interpret as low flux lip activity between the high flux periods this trend of high and low flux os concentration pulses with mantle like osi values during the high flux periods is found in another kwis core usgs portland 1 deposited to the north of iona 1 and in core deep sea drilling project dsdp site 530 hole a hereafter dsdp 530a drilled off shore namibia in the angola basin deposited in the southern hemisphere before and throughout the iona 1 core oae 2 interval hse abundance patterns indicate a mantle source for the unradiogenic os and are not consistent with an extraterrestrial impact trigger or contribution to lip activity during oae 2 this evidence for multiple high flux pulses of lip activity driving ocean deoxygenation has implications for the modern ocean which is currently experiencing deoxygenation these results provide new constraints on subsequent high flux periods that extended the event the first high flux period started 60 kyr after our selection of the onset of the cie the second and third high flux periods started 270 and 400 kyr after the onset of the cie respectively after the third high flux period 13corg and os isotope ratios shifted back to pre excursion values over 585 kyr in the iona 1 core oae 2 lasted for 1 04 0 12 myr based on our selection of the cie

the northern gulf of mexico during oae2 and the relationship between water depth and black shale development despite their name oceanic anoxic events oaes are not periods of uniform anoxia and black shale deposition in ancient oceans shelf environments account for the majority of productivity and organic carbon burial in the modern ocean and this was likely true in the cretaceous as well however it is unlikely that the mechanisms for such an increase were uniform across all shelf environments some like the northwest margin of africa were characterized by strong upwelling but what might drive enhanced productivity on shelves not geographically suited for upwelling to address this we use micropaleontology carbon isotopes and sedimentology to present the first record of oceanic anoxic event 2 oae2 from the northern gulf of mexico shelf here oae2 occurred during the deposition of the well oxygenated inner neritic lower estuarine lower tuscaloosa sandstone the overlying organic rich oxygen poor marine tuscaloosa shale is entirely turonian in age we trace organic matter enrichment from the spinks core into the deepwater gulf of mexico where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the cenomanian turonian boundary interval redox change and organic matter preservation across the gulf of mexico shelf were driven by sea level rise prior to the early turonian highstand which caused the advection of nutrient rich oxygen poor waters onto the shelf this results in organic matter mass accumulation rates 1 2 orders of magnitude lower than upwelling sites like the nw african margin but it likely occurred over a much larger geographic area suggesting that sea level rise was an important component of the overall increase in carbon burial during oae2

considerations in phase estimation and event location using small aperture regional seismic arrays the global monitoring of earthquakes and explosions at decreasing magnitudes necessitates the fully automatic detection location and classification of an ever increasing number of seismic events many seismic stations of the international monitoring system are small aperture arrays designed to optimize the detection and measurement of regional phases collaboration with operators of mines within regional distances of the arces array together with waveform correlation techniques has provided an unparalleled opportunity to assess the ability of a small aperture array to provide robust and accurate direction and slowness estimates for phase arrivals resulting from well constrained events at sites of repeating seismicity a significant reason for the inaccuracy of current fully automatic event location estimates is the use of f k slowness estimates measured in variable frequency bands the variability of slowness and azimuth measurements for a given phase from a given source region is reduced by the application of almost any constant frequency band however the frequency band resulting in the most stable estimates varies greatly from site to site situations are observed in which regional p arrivals from two sites far closer than the theoretical resolution of the array result in highly distinct populations in slowness space this means that the f k estimates even at relatively low frequencies can be sensitive to source and path specific characteristics of the wavefield and should be treated with caution when inferring a geographical backazimuth under the assumption of a planar wavefront arriving along the great circle path moreover different frequency bands are associated with different biases meaning that slowness and azimuth station corrections commonly denoted sascs cannot be calibrated and should not be used without reference to the frequency band employed we demonstrate an example where fully automatic locations based on a source region specific fixed parameter template are more stable than the corresponding analyst reviewed estimates the reason is that the analyst selects a frequency band and analysis window which appears optimal for each event in this case the frequency band which produces the most consistent direction estimates has neither the best snr or the greatest beam gain and is therefore unlikely to be chosen by an analyst without calibration data

production and preservation of organic matter the significance of iron 1 iron fertilization has been previously recognized as a potential mechanism for enhanced organic matter burial in marine sediments however the singular view of iron as a control on primary production overlooks its role in sedimentary diagenesis a factor that must be evaluated when considering organic matter accumulation this study examines the role of iron as a buffer of pore water sulfide and its implications for marine organic matter burial biogeochemical model experiments indicate that dissolved sulfide buildup in surficial marine sediments is highly sensitive to reactive iron concentration a reduction in reactive iron concentration can initiate dissolved sulfide accumulation the consequences of which include inhibition of bioturbation bioirrigation a decrease in oxygen exposure time and enhanced organic matter burial alternatively an increase in reactive iron concentration can serve to decrease organic matter burial the coupling of iron and phosphorous cycling within marine sediments provides an important positive feedback and therefore this mechanism is designated the sulfide buffer phosphorous trap hypothesis given sufficient organic carbon supply carbonate rich and opal rich sediments should be especially prone to the development of sulfidic conditions because of a deficiency in terrigenous iron widespread chalk and marl deposition during the cretaceous in association with the evolutionary expansion of calcareous plankton may have predisposed many benthic marine environments to the accumulation of toxic hydrogen sulfide and fostered the development of oceanic anoxic events comparison of model results with proxy data from oceanic anoxic event ii middle cretaceous suggests a complex role of iron as a control on both organic matter production and preservation

high resolution hyperspectral based continuous mineralogical and total organic carbon analysis of the eagle ford group and associated formations in south texas hyperspectral sensing is used to generate mineral maps of a fine grained vertical eagle ford group cored section and underlying buda limestone and del rio formation in south texas this technology produces a map that shows the distribution of minerals on the core surface three different cameras within the hyperspectral core imaging system were used to image a 99 1 m 325 ft core a 1 line scan camera which produces a high resolution red green blue 120 m natural color photograph of the dry core from the visible light spectrum 2 short wave infrared swir spectrometer 300 500 m resolution and 3 long wave infrared lwir spectrometer 300 500 m resolution in 2016 the introduction of a new high resolution lwir spectrometer made it possible to identify minerals in cores that were not detected by previous swir systems high resolution hyperspectral imaging technology using both the swir and lwir spectra provides a significant step toward quantifying mineralogy and total organic carbon hyperspectral imaging is a powerful tool for studying textural and fabric relationships because it detects and highlights the major mineralogical changes that occur between depositional beds and among depositional features calcite compositional variations and cyclicity appear to be closely related the sr rich calcite appears to indicate a smaller allochem size dominance as well as the slower sedimentation rates that are required for nannofossils to settle from suspension finally the observed diagnostic cyclicity of the lower eagle ford can be related to coccolithophore productivity

cenomanian sequence stratigraphy and sea level fluctuations in the tarfaya basin sw morocco we investigated the sequence architecture of two expanded cenomanian successions along a depth transect in the tarfaya basin sw morocco and correlated these successions to published records from northwest europe and india changes in terrigenous material carbonate and organic carbon content carbonate microfacies and foraminiferal biofacies as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts we identified two main transgressive cycles in the lower and middle upper cenomanian separated by a major regression at the early middle cenomanian transition sequence boundary ce 3 this regressive interval is characterized by lagoonal low stand deposits indicating an overall sealevel fall of more than 30 m superimposed on the two main transgressive cycles there are 11 third order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations 400 ka period positive carbon isotope excursions in the middle cenomanian 96 0 ma and latest cenomanian 94 0 ma following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation we suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity nodes which probably coincided with glacioeustatic lowstands

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

lg attenuation in the central and eastern united states as revealed by the earthscope transportable array abstract lg waveforms recorded by earthscope s transportable array ta are used to estimate lg q 0 in the central and eastern united states ceus attenuation is calculated based on lg spectral amplitudes filtered at a narrow band from 0 5 to 1 5 hz two station and reverse two station techniques are used to calculate q 0 values 39 events occurring from 2010 to 2012 and ranging from magnitude 3 to magnitude 6 are used in this study 39 258 and 4 627 interstation q 0 values are determined using the two station and reverse two station techniques respectively the results show northeast trending high q 0 regions low attenuation ranging from eastern new mexico to wisconsin regions of low q 0 high attenuation are seen along the minnesota wisconsin border the gulf coastal plain gcp along the south dakota nebraska border and along the oklahoma texas border a positive correlation between heat flow sediment thickness recent tectonic activity fluids and low q 0 was observed areas with low heat flow thin sediment cover no recent tectonic activity and a lack of fluids were observed to have consistently high q 0 these new models use a greater amount of data attain more coverage than previous studies and better constrain attenuation this increase in detail can improve high frequency ground motion predictions of future large earthquakes for more accurate far field hazard assessment and improve the overall understanding of the structure and assemblage of the ceus

extreme wave statistical methods and implications for coastal analyses abstract this work reviews methods for extreme value analysis of ocean waves including site specific univariate analysis environmental contour analysis and spatial analysis a variation of regional frequency analysis is proposed based on the hypothesis that the distribution of extreme wave events at different sites within a homogeneous region are identical except for a shift due to a location parameter with this assumption the shape and scale parameters of the distribution can be determined with greater certainty by pooled measurements while the spatial variation is captured by the location parameter which is equal to a threshold wave height and may be more reliably sourced from a computational model as compared to the extreme values themselves this approach attempts to overcome the lack of accuracy of most wave models in extreme wave events by basing the shape and scale parameters on measurements while using a wave hind cast in a range where it is acceptably accurate to find the spatially varying location parameter the methods are applied to a case study of the canadian pacific coast un sheltered measurement sites were found to satisfy statistical homogeneity and were used to define a regional shifted extreme value distribution a high resolution numerical model was used to define the spatially varying location parameter equal to the 98th percentile of significant wave heights in general the results are satisfactory and suggest this approach may be a useful tool in understanding the spatial variability of wave extremes however it is acknowledged that this approach relies on the availability of multiple measurement sites with sufficient duration to support extreme value analysis

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

orbital time scale and new c isotope record for cenomanian turonian boundary stratotype previous time scales for the cenomanian turonian boundary ctb interval containing oceanic anoxic event ii oae ii vary by a factor of three in this paper we present a new orbital time scale for the ctb stratotype established independently of radiometric biostratigraphic or geochemical data sets update revisions of ctb biostratigraphic zonation and provide a new detailed carbon isotopic record for the ctb study interval the orbital time scale allows an independent assessment of basal biozone ages relative to the new ctb date of 93 55 ma gts04 the d 13 corg data document the abrupt onset of oae ii significant variability in d 13 corg values and values enriched to almost 222 these new data underscore the difficulty in defining oae ii termination using the new isotope curve and time scale estimates of oae ii duration can be determined and exported to other sites based on integration of well established chemostratigraphic and biostratigraphic datums the new data will allow more accurate calculations of biogeochemical and paleobiologic rates across the ctb

seismic amplitude tomography for crustal attenuation beneath china summary amplitude tomography reconstructs seismic attenuation directly from recorded wave amplitudes we have applied the tomography to amplitude data reported in the annual bulletin of chinese earthquakes and interpreted the regionally varying crustal attenuation in terms of tectonics the seismic amplitudes were originally recorded for determining the m l and m s magnitudes they generally correspond to the maximum amplitudes of the horizontal components of the short period s waves and intermediate period rayleigh waves both sets of measurements are sensitive to crustal structure the peak amplitudes from m l amplitudes spread spherically with significant dispersion and scattering m s amplitudes show cylindrical spreading with little dispersion average crustal q values for attenuation at 1 hz are 737 and 505 for m l and m s respectively with substantial regional variations frequency dependence in the attenuation is also indicated regions with the lowest attenuation high q values are beneath the south china block sichuan basin ordos platform the daxinganling and the korea craton these tend to be tectonically inactive regions which are generally dominated by intrusive and cratonic rocks in the upper crust regions with the highest attenuation low q values are beneath bohai basin yunnan eastern songpan ganzi terrain margins of the ordos platform and the qilian shan these are predominantly active basins grabens and fold belts the continental margin also highly attenuates both s and surface waves

seismic attenuation tomography in southwestern china insight into the evolution of crustal flow in the tibetan plateau abstract crustal flow in southwestern china is commonly attributed to the continental collision between the indian and the eurasian plates therefore studying crustal flow in this area can provide valuable insight into the collisional process the quality factor q is an indicator of seismic wave attenuation that provides constraints on lithology rheology and geodynamic processes which are vital for interpreting the nature of the crustal flow in a given region in this study we used local seismic waveforms to obtain regional attenuation models for p qp and s qs waves in the sichuan yunnan region syr the emeishan large igneous province elip is characterized by high qp and qs values in the middle yunnan block myb at depths greater than 5 km the qp and qs values in most of the fault zones surrounding the myb were lower than 300 indicating that the material within crustal faults causes high waveform attenuation our results suggest that the crustal flow was diverted into two channels in the northern myb due to resistance from the elip to illuminate the tectonic dynamics of the syr we propose a simple model that explains both the evolution of the crustal flow and the variation in the seismic wave attenuation

sedimentary mercury enrichments as a marker for submarine large igneous province volcanism evidence from the mid cenomanian event and oceanic anoxic event 2 late cretaceous oceanic anoxic event 2 oae 2 during the cenomanian turonian transition 94 ma was the largest perturbation of the global carbon cycle in the mid cretaceous and can be recognized by a positive carbon isotope excursion in sedimentary strata although oae 2 has been linked to large scale volcanism several large igneous provinces lips were active at this time e g caribbean high arctic madagascan ontong java and little clear evidence links oae 2 to a specific lip the mid cenomanian event mce 96 ma identified by a small 1 positive carbon isotope excursion is often referred to as a prelude to oae 2 however no underlying cause has yet been demonstrated and its relationship to oae 2 is poorly constrained here we report sedimentary mercury hg concentration data from four sites three from the southern margin of the western interior seaway and one from demerara rise in the equatorial proto north atlantic ocean we find that in both areas increases in mercury concentrations and hg toc ratios coincide with the mce and the oae 2 however the increases found in these sites are of a lower magnitude than those found in records of many other mesozoic events possibly characteristic of a marine rather than atmospheric dispersal of mercury for both events combined the new mercury data presented here are consistent with an initial magmatic pulse at the time of the mce with a second greater pulse at the onset of oae 2 possibly related to the emplacement of lips in the pacific ocean and or the high arctic

lg attenuation in northeast china using necessarray data nishath r ranasinghe 1 andrea c gallegos 1 andrea r trujillo 1 2 alexander r blanchette 1 eric a sandvol 3 james ni 1 thomas m hearn 1 youcai tang 4 5 stephen p grand 4 fenglin niu 5 6 yongshun j chen 7 jieyuan ning 7 hitoshi kawakatsu 8 satoru tanaka9 and masayuki obayashi9 1department of physics new mexico state university las cruces nm 88001 usa e mail nrana001 nmsu edu 2apache corporation 303 veterans airpark lane 600 midland tx 79705 usa 3department of geological sciences university of missouri 101 geology bldg columbia mo 65211 usa 4jackson school of geosciences the university of texas at austin austin tx 78712 usa 5state key laboratory of petroleum resource and prospecting and unconventional natural gas institute china university of petroleum beijing 102249 china 6department of earth science ms 126 rice university houston tx 77005 usa 7institute of theoretical and applied geophysics sess peking university beijing china 8earthquake research institute the university of tokyo tokyo japan 9institute for frontier research on earth and evolution japan agency for marine earth science and technology yokosuka japan

tomographic inversion of pn travel times in china 1 pn travel times are useful for studying crustal and uppermost mantle structure and regional tectonics because they are affected by crustal velocity and thickness as well as uppermost mantle velocity and anisotropy we obtained 57 740 pn travel time picks from 5433 earthquakes and 307 stations from chinese national and provincial earthquake bulletins and the international seismological center bulletins to invert for pn velocity variation and anisotropy and station delays in china our inversion reveals significant features that correlate with surface geology the main results are as follows 1 the pn velocities show a mosaic of very fast and very slow anomalies mirroring the heterogeneous geology of china at the surface the pn velocities are high beneath the major basins in the west sichuan qaidam west tarim tulufan and junggar and low in areas of active volcanoes myanmar and western yunnan and quaternary volcanism in northern tibet in seismically active areas in north china and tien shan and in the southern part of south china the hainan plume 2 the pn anisotropy beneath the major basins in the west is generally weak strong anisotropy is found beneath high deformation regions the tibetan plateau southeastern margin of the tibetan plateau western tien shan and part of north china suggesting the anisotropy is likely related to recent large scale tectonic activity 3 a large area of north china shows prominent low pn velocity beneath archean basement with thin crust our observations are consistent with rifting lithospheric thinning and mantle upwelling in the region the pn anisotropy is consistent with a dextral simple shear in the nne direction in the lithosphere mantle during the last and ongoing major deformation period 4 the pn velocity in northern tibet is generally lower than that in the south southern tibet has significant e w structure low velocity anomalies can be traced from northern tibet across southwestern tibet and south central tibet to near the india plate anisotropy is absent beneath much of the himalaya block but consistent anisotropy with e w fast direction is present beneath the lhasa block and large anisotropy up to 4 is observed in low velocity regions of the northern and western tibet complex station delays in the eastern margin of the plateau suggest that the whole crust may be highly deformed the anisotropy pattern in the southeastern margin of the tibetan plateau suggests a mantle lithospheric deformation similar to the clockwise rotation of material observed at the surface 5 crustal thicknesses inferred from our station delays are consistent with previous models which correlate well with surface topography

application of regional phase amplitude tomography to seismic verification we have applied tomographic techniques to amplitude data to quantify regional phase path effects for use in source discrimination studies tomography complements interpolation kriging methods by extending our ability to apply path corrections into regions devoid of calibration events as well as raising levels of confidence in the corrections because of their more physical basis our tomography technique solves for resolvable combinations of attenuation source generation site and spreading terms first difference regularization is used to remove singularities and reduce noise effects in initial tests the technique was applied to a data set of 1488 1 0 hz p g l g amplitude ratios from 13 stations for paths inside a 30 by 40 box covering western china and surrounding regions tomography reduced variance 60 relative to the power law distance correction traditionally applied to amplitude ratios relative p g l g attenuation varied with geologic region with low values in tibet intermediate values in basins and high values for platforms and older crust spatial patterns were consistent with previous path effect studies in asia especially local earthquake coda q relative spreading was consistent with expected values for p g and l g relative site terms were similar to one another yet some tradeoff with attenuation was evident tomography residuals followed systematic trends with distance which may result from the evolution from direct to coda phases focusing model tradeoff or data windowing effects examination of the residuals using a kriging interpolator showed coherent geographical variations indicating unmodeled path effects the residual patterns often follow geological boundaries which could result from attenuating zones or minor blockages that are too thin to be resolved or that have anisotropic effect on regional phases these results will guide efforts to reparameterize tomography models to more effectively represent regional wave attenuation and blockage the interpolated residuals also can be combined with predictions of the tomographic model to account for path effects in discrimination studies on a station by station basis

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

tomographic regionalization of crustal lg q in eastern eurasia 1 we measure q of crustal lg waves in eastern eurasia using the reliable two station methods more than 5 000 spectral ratios are collected over 594 interstation paths and are used to determine values of lg q0 and q at 1 hz and its frequency dependence over these paths these values are used to derive tomographic models of laterally varying q0 and with resolutions between 4 and 10 the q0 model contains values that vary between 100 and 900 q0 are the lowest in the tibetan plateau increase to moderate levels towards the east and north and reach maxima in the siberian and eastern europe cratons q0 values correlate well with regional tectonics most values are between 0 14 and 0 50 with a mean of 0 18 these values are lower than those obtained previously using either an lg coda q method or a method of simultaneous inversion of source spectra and q

salsa3d a tomographic model of compressional wave slowness in the earth s mantle for improved travel time prediction and travel time prediction uncertainty abstract the task of monitoring the earth for nuclear explosions relies heavily on seismic data to detect locate and characterize suspected nuclear tests motivated by the need to locate suspected explosions as accurately and precisely as possible we developed a tomographic model of the compressional wave slowness in the earth s mantle with primary focus on the accuracy and precision of travel time predictions for p and pn ray paths through the model path dependent travel time prediction uncertainties are obtained by computing the full 3d model covariance matrix and then integrating slowness variance and covariance along ray paths from source to receiver path dependent travel time prediction uncertainties reflect the amount of seismic data that was used in tomography with very low values for paths represented by abundant data in the tomographic data set and very high values for paths through portions of the model that were poorly sampled by the tomography data set the pattern of travel time prediction uncertainty is a direct result of the off diagonal terms of the model covariance matrix and underscores the importance of incorporating the full model covariance matrix in the determination of travel time prediction uncertainty the computed pattern of uncertainty differs significantly from that of 1d distance dependent travel time uncertainties computed using traditional methods which are only appropriate for use with travel times computed through 1d velocity models

evaluation of nga west2 and chinese ground motion prediction equations for developing seismic hazard maps of mainland chinaevaluation of nga west2 and chinese gmpes for developing seismic hazard maps of mainland china

cyanobacteria proliferation in the cenomanian turonian boundary interval of the apennine carbonate platform immediate response to the environmental perturbations associated with oae 2

paleo redox conditions during oae 2 reflected in demerara rise sediment geochemistry odp leg 207 abstract cretaceous black shales deposited under severe oxygen depletion are carriers of proxy signals for paleoenvironmental conditions using high resolution patterns of iron and sulfur speciation stable sulfur isotope discrimination and trace element enrichment from black shale sequences of sites 1258 and 1260 we identified alterations of the depositional environment during the cenomanian turonian boundary event oae 2 in the southern north atlantic odp leg 207 demerara rise changes in redox conditions are suggested by high ratios of reactive to total iron which indicate that pyrite was formed both in the water column and within the sediment this corresponds to euxinic paleoenvironmental conditions with at least temporarily free dissolved sulfide in the water column a situation similar to the modern deep black sea in addition besides fixation of sulfide as iron sulfide organic matter acted as an important sulfur trap during early diagenesis stable sulfur isotope fractionation went through a minimum within the oae 2 interval indicating enhanced sulfur isotope discrimination during highest burial of organic matter om potentially due to lower burial efficiency of reduced sulfur and or a higher contributions from the oxidative part of the sulfur cycle e g in the water column or the surface sediments elevated fe al and co al values within the cenomanian turonian interval confirm euxinic conditions but at the same time require a zone where reducing but non sulfidic conditions prevail allowing reductive fe and co mobilization in oxygen depleted nearshore sediments the existence of an expanded oxygen minimum zone omz is demonstrated by extremely low mn al ratios a change in the trace metal tm inventory of seawater is postulated from a decline in seawater derived tm enrichment because hypoxic or even euxinic environments form an important sink for tm the enlargement of euxinic depositional areas at the global onset of black shale deposition during oae 2 have likely led to a drawdown of the seawater tm reservoir

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

age and paleoenvironment of the cenomanian turonian global stratotype section and point at pueblo colorado biostratigraphy and stable isotopes indicate that the global stratotype section and point gssp at pueblo contains an essentially complete sedimentary record across the global ocean anoxic event oae 2 and the cenomanian turonian boundary the oae 2 d 13 c shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression which at its peak was marked by an incursion of oxygen rich waters creating a benthic oxic zone that lasted about 100 ky a mid cenomanian d 13 c shift sea level transgression and faunal turnover occurred about 2 my before oae 2 d 18 o values of the planktic foraminifer hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions whereas dominance by the low oxygen tolerant heterohelix species indicates a well developed oxygen minimum zone omz for most of the middle to late cenomanian and early turonian profound faunal changes accompanied these oceanographic events including the extinction of 30 of the species assemblage and an equal gain in evolutionary diversification though the overall combined relative abundances of outgoing and incoming species were less than 2 and 4 respectively of the total assemblages the faunal turnover began with the sea level transgression and rapid increase in d 13 c values and accelerated with the influx of oxygen rich deep water increased water mass stratification and competition during the benthic oxic zone the incursion of oxygen rich deep waters at this time was also observed in morocco and may represent a global event of a still unknown source d 2003 elsevier b v all rights reserved

crustal radial anisotropy across eastern tibet and the western yangtze craton 1 phase velocities across eastern tibet and surrounding regions are mapped using rayleigh 8 65 s and love 8 44 s wave ambient noise tomography based on data from more than 400 program for array seismic studies of the continental lithosphere and chinese earthquake array stations a bayesian monte carlo inversion method is applied to generate 3 d distributions of vsh and vsv in the crust and uppermost mantle from which radial anisotropy and isotropic vs are estimated each distribution is summarized with a mean and standard deviation but is also used to identify highly probable structural attributes which include 1 positive midcrustal radial anisotropy vsh vsv across eastern tibet spatial average 4 8 1 4 that terminates abruptly near the border of the high plateau 2 weaker 1 0 1 4 negative radial anisotropy vsh vsv in the shallow crust mostly in the songpan ganzi terrane 3 negative midcrustal anisotropy 2 8 0 9 in the longmenshan region 4 positive midcrustal radial anisotropy 5 4 1 4 beneath the sichuan basin and 5 low vs in the middle crust 3 427 0 050 km s of eastern tibet midcrustal vs 3 4 km s perhaps consistent with partial melt is highly probable only for three distinct regions the northern songpan ganzi the northern chuandian and part of the qiangtang terranes midcrustal anisotropy provides evidence for sheet silicates micas aligned by deformation with a shallowly dipping foliation plane beneath tibet and the sichuan basin and a steeply dipping or subvertical foliation plane in the longmenshan region near vertical cracks or faults are believed to cause the negative anisotropy in the shallow crust underlying tibet

spectral inversion of lg from earthquakes a modified method with applications to the 1995 western texas earthquake sequence spectral inversion of lg from earthquake sources is subject to significant errors due to random and systematic deviation of the lg spectra from idealized theoretical models i present an analysis of these errors and demonstrate that their effects tend to increase with decreasing frequency and recording distance i propose modifications to the inverse method of xie 1993 to reduce these errors the modifications include a more robust q estimator and the added capability of incorporating a priori knowledge into the inversion the modified method is applied to lg spectra from the 1995 western texas earthquake mw 5 7 i measured average two station q values for selected station pairs as well as the source rise time of the mainshock with an empirical green s function approach these served as a priori knowledge for the simultaneous inversion for lg seismic moment m corner frequency fc and path q the result of the inversion indicates that lg source radiation is nearly isotropic the m and fc values estimated using lg from the mainshock and two aftershocks are typical for lg from central and eastern north american earthquakes with m scaling with fc 4 and m and fc being 3 3 1016 n m and 0 3 hz respectively for the mainshock the 1 hz lg q correlates with tectonic environments increasing from about 200 for westerly paths to above 700 for easterly paths two station q measurements suggest that as previously discovered for eurasia the frequency dependence of lg q may be variable with distance if the distance spans a wide range 103 km

yield estimates of nevada test site explosions obtained from seismic lg waves a methodology is presented for determining the yield of underground nuclear explosions from lg wave amplitudes the methodology is applied to nevada test site nts explosions for which the data from short period vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water saturated rock source conditions the latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the united states and in the french sahara suggesting that they may be applicable to all continental areas if so they also can provide an estimate of the bias of mb p magnitudes between different continental sites for example the lg data from nts explosions indicate a 0 31 0 02 magnitude unit bias between nts and eastern north america similar to the approximately 0 33 unit bias found between western and eastern north america previously by use of earthquake data

crustal flow pattern beneath the tibetan plateau constrained by regional lg wave q tomography abstract as a prominent geophysical anomaly unusually high seismic wave attenuation is observed in the crust and upper mantle of the tibetan plateau particularly along its northern area theoretical and laboratory investigations show that the strong seismic attenuation can indicate high temperatures and partial melting which may decrease the viscosity of the material and cause it to flow thus seismic attenuation distribution may provide useful constraints to the crust flows if they exist using lg wave q tomography we construct a 0 05 10 0 hz broadband high resolution crust attenuation model for the tibetan plateau and its surrounding regions the maximum spatial resolution is approximately 1 0 1 0 in well covered areas and for frequencies between 0 05 and 1 5 hz this attenuation model reveals an apparent low qlg belt stretching along the northern and eastern tibetan plateau combining the lg wave q model with other geophysical data two possible crust flow channels are found in the tibetan plateau the main flow channel is from north to east and then turns to southeastern tibet along the western edge of the rigid sichuan basin while a second channel starts from southern tibet and crosses the eastern himalayan syntaxis

orbital forcing of organic carbon burial in the proto north atlantic during oceanic anoxic event 2 the cenomanian turonian c t intervals at dsdp sites 105 and 603b from the northern part of the proto north atlantic show high amplitude short term cyclic variations in total organic carbon toc content the more pronounced changes in toc are also reflected by changes in lithology from green claystones toc 1 although their depositional history was different the individual toc cycles at sites 105 and 603b can be correlated using stable carbon isotope stratigraphy sedimentation rates obtained from the isotope stratigraphy and spectral analyses indicate that these cycles were predominately precession controlled the coinciding variations in hi oi 13corg and the abundance of marine relative to terrestrial biomarkers as well as the low abundance of lignin pyrolysis products generated from the kerogen of the black claystones indicate that these cyclic variations reflect changes in the contribution of marine organic matter om the cooccurrence of lamination enrichment of redox sensitive trace metals and presence of molecular fossils of pigments from green sulfur bacteria indicate that the northern proto north atlantic ocean water column was periodically euxinic from the bottom to at least the base of the photic zone 150 m during the deposition of the black claystones in contrast the green claystones are bioturbated are enriched in mn do not show enrichments in redox sensitive trace metals and show biomarker distributions indicative of long oxygen exposure times indicating more oxic water conditions at the same time there is evidence e g abundance of biogenic silica and significant 13c enrichment for oc of phytoplanktic origin for enhanced primary productivity during the deposition of the black claystones we propose that increased primary productivity periodically overwhelmed the oxic om remineralisation potential of the bottom waters resulting in the deposition of om rich black claystones because the amount of oxygen used for om remineralisation exceeded the amount supplied by diffusion and deep water circulation the northern proto north atlantic became euxinic during these periods both sites 105 and 603b show trends of continually increasing toc contents and hi values of the black claystones up section which most likely resulted from both enhanced preservation due to increased anoxia and increased production of marine om during oceanic anoxic event 2 oae2

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

attenuation tomography of the earth s mantle a review of current status resolving the lateral variations of attenuation in the deep mantle by tomographic methods holds potential for constraining its thermal structure and dynamics it is a challenging subject which has been addressed by only a few studies until now we here review the main motivations behind pursuing this challenge the difficult issues involved in separating effects of anelastic attenuation from scattering and focusing due to propagation in 3 d elastic structure and finally discuss the current status of global attenuation tomography

integrated ground based hyperspectral imaging and geochemical study of the eagle ford group in west texas abstract this study used ground based hyperspectral imaging to map an outcrop of the eagle ford group in west texas the eagle ford group consists of alternating layers of mudstone wackestone grainstone packstone facies and volcanic ash deposits with high total organic content deposited during the cenomanian turonian time period it is one of the few unconventional source rock and reservoirs that have surface representations ground based hyperspectral imaging scanned an outcrop and hand samples at close ranges with very fine spatial resolution centimeter to sub millimeter spectral absorption modeling of clay minerals and calcite with the modified gaussian model mgm allowed quantification of variations of mineral abundances petrographic analysis confirmed mineral identifications and shed light on sedimentary textures and major element geochemistry supported the mineral quantification mineral quantification resulted in mapping of mudstone wackestone grainstone packstone facies and bentonites volcanic ash beds the lack of spatial associations between the grainstones and bentonites on the outcrop calls into question the hypothesis that the primary productivity is controlled by iron availability from volcanic ash beds enrichment of molybdenum mo and uranium u indicated unrestricted marine paleo hydrogeology and anoxic to euxinic paleo redox bottom water conditions hyperspectral remote sensing data also helped in creating a virtual outcrop model with detailed mineralogical compositions and provided reservoir analog to extract compositional and geo mechanical characteristics and variations the utilization of these new techniques in geo statistical analysis provides a workflow for employing remote sensing in resource exploration and exploitation

seismic lg wave q tomography in and around northeast china 1 we investigate regional variations in the lg wave quality factor q in northeast china and its vicinity with a tomographic method digital seismic data recorded at 20 broadband stations from 125 regional events are used to extract lg wave spectra tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0 05 and 10 0 hz we simultaneously invert for the lg wave q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the q model and source function the best spatial resolution is approximately 1 1 in well covered areas for frequencies between 0 4 and 2 0 hz the lg q shows significant regional variations and an apparent relationship with regional geology we use a statistical method to investigate the regional variations of lg q and their frequency dependence the average q0 1 hz lg q in the entire investigated region is 414 sedimentary basins are usually characterized by lower average q0 values from 155 to 391 while volcanic mountain areas have relatively high average q0 values from 630 to 675 lg q generally increases with increasing frequency however the frequency dependence has complex nonlinear features on a double logarithmic scale indicating that the commonly adopted power law relationship may be oversimplified in a broad frequency band the frequency dependence varies in different geological areas with larger variations seen at lower frequencies

a new plumbing system framework for mantle plume related continental large igneous provinces and their mafic ultramafic intrusions abstract the magmatic components of continental large igneous provinces lips include flood basalts and their plumbing system of giant mafic dyke swarms radiating linear and the recently discovered circumferential type mafic sill provinces a lower crustal magmatic underplate mafic ultramafic m um intrusions associated silicic magmatism and associated carbonatites and kimberlites this paper proposes a new plumbing system framework for mantle plume related continental lips that incorporates all of these components and provides a context for addressing key thematic aspects such as tracking magma batches upstream and downstream and their geochemical evolution assessing the setting of m um intrusions and their economic potential interpreting deep magmatic component identified by geophysical signatures and estimating magnitudes of extrusive and intrusive components with climate change implications this plumbing system model and its associated implications needs to be tested against the rapidly improving lip record

a perturbed hydrological cycle during oceanic anoxic event 2 the late cretaceous oceanic anoxic event 2 oae2 ca 94 ma was one of the largest global carbon cycle perturbations during the phanerozoic oae2 represents an important although extreme case study for modern trends because widespread anoxia and enhanced organic carbon burial during oae2 were linked to exceptionally warm climates and high atmospheric co 2 concentrations however the consequences of this warmth for the hydrological cycle remain poorly understood hampering our understanding of its impact on biogeochemical cycles during this greenhouse episode here we show evidence for changes in the hydrological cycle during oae2 based on combined geochemical and palynological data for the stratigraphically expanded coastal oae2 succession at bass river located on the new jersey shelf ocean drilling program leg 174ax eastern united states paleothermometry based on tex86 indicates sea surface warming at the onset of oae2 and a subsequent pronounced cooling event palynological data show that these changes in temperature were associated with strong variations in precipitation and runoff we suggest that an acceleration of the hydrological cycle during oae2 played a key role in supplying nutrients to coastal waters and enhancing stratification thus contributing to the development of ocean anoxia

origin of limestone marlstone cycles astronomic forcing of organic rich sedimentary rocks from the cenomanian to early coniacian of the cretaceous western interior seaway usa abstract we present an integrated multidisciplinary study of limestone marlstone couplets from a continuously cored section including parts of the upper buda limestone the entire eagle ford group boquillas formation and lower austin chalk from the shell iona 1 research borehole texas usa which provides a 8 million year myr distal clastic sediment starved intrashelf basin record of the early cenomanian to the earliest coniacian stages results show that despite variable yet minimal diagenetic overprints several unambiguous primary environmental signals are preserved and support greater water mass ventilation and current activity promoting increased silica carbonate productivity during the deposition of limestone beds compared to deposition of marlstone beds which reflect greater organic matter productivity and preservation furthermore our astronomical analyses demonstrate that the limestone marlstone couplets in the iona 1 core reflect climatic forcing driven by solar insolation resulting from integrated milankovitch periodicities in particular we propose that obliquity and precession forcing on the latitudinal distribution of solar insolation may have been responsible for the observed lithological and environmental variations through the cenomanian turonian and coniacian in this mid latitude epicontinental sea setting our data also suggests that rhythmic lithological alternations deposited in greenhouse periods in general may simply reflect climate driven cycles related to earth sun dynamics without the need to invoke significant sea level variations

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

mineralogical composition and total organic carbon quantification using x ray fluorescence data from the upper cretaceous eagle ford group in southern texas six southern texas eagle ford cores were investigated to quantify mineralogical composition and total organic carbon toc machine learning of the x ray fluorescence xrf data set was conducted using neural network analysis to predict mineralogies for l1 l2 and l3 and toc for l1 l2 l3 iona 1 innes 1 and well x inees 1 and well x were used as blind tests to check the quality of the developed models the online neural designer software was used to perform the training process and develop models quantitative laboratory measured x ray diffraction xrd mineralogies and toc were used to conduct the training and develop high resolution semiquantitative models and the derived mineralogic and organic matter models were found to be promising the modeled mineralogy and toc represent continuous relative abundances which are far more significant than scattered individual xrd and toc point measurements the significance of this study is that it allows for the use of relatively inexpensive and nondestructive xrf analysis that requires minimal sample preparation to construct high resolution mineral abundances and toc content with modern advances in technology xrf can now be measured on drill cuttings in real time while drilling is occurring allowing operators to use the proposed method to construct semiquantitative mineralogical and toc models for evaluating placement of laterals in prospective intervals and designing completion techniques accordingly

high resolution regional seismic attenuation tomography in eastern tibetan plateau and adjacent regions 1 the q of regional seismic phases lg and pg within the crust is assumed as a proxy for crustal q and q which is used as a constraint of crustal rheology we measure regional phase q of the eastern tibetan plateau and adjacent areas this method eliminates contributions from source and site responses and is an improvement on the two station method tsm we have generated tomographic images of crustal attenuation anomalies with resolution as high as 1 in general we observe low q in the northernmost portions of the tibetan plateau and high q in the more tectonically stable regions such as the interior of the qaidam basin the calculated site responses appear to correlate with topography or sediment thickness furthermore the relationship between earthquake magnitudes and calculated source terms suggest that the rtm method effectively removes the source response and may be used as an alternative to source magnitude

broad band lg attenuation modelling in the middle east summary we present a broad band tomographic model oflg attenuation in the middle east derived from source and site corrected amplitudes absolute amplitude measurements are made on handselected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region a conjugate gradient method is used to tomographically invert the amplitude data set of over 8000 paths over a 45 40 region of the middle east we solve for q variation as well as site and source terms for a wide range of frequencies ranging from 0 5 to 10 hz we have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment this facilitates the use of the model to predict the expected amplitudes of new events an important consideration for earthquake hazard or explosion monitoring applications the attenuation results have a strong correlation to tectonics shields have low attenuation whereas tectonic regions have high attenuation with the highest attenuation at 1 hz found in eastern turkey the results also compare favourably to other studies in the region made using lg propagation efficiency lg pg amplitude ratios and two station methods we tomographically invert the amplitude measurements for each frequency independently in doing so it appears the frequency dependence of attenuation in all regions is not compatible with the power law representation of q f an assumption that is often made

estimating the model resolution matrix for large seismic tomography problems based on lanczos bidiagonalization with partial reorthogonalization summary the propack package developed by larsen is able to efficiently and accurately estimate singular values and vectors for large matrices based on the lanczos bidiagonalization with partial reorthogonalization we incorporate the pavtial reorthogonalization package propack package into the double difference seismic tomography code tomodd and estimate the model resolution matrix for large seismic tomography problems compared to previous least squares qr lsqr based methods for estimating the model resolution matrix the propack based method calculates the full resolution matrix and thus gives a complete description of how well the model is resolved several observations are drawn from the application to data from the 2001 eruption of mt etna for this example it is reasonable to use ray sampling density information to characterize the model resolution qualitatively the model resolution resulting from just velocity inversion bears a close linear relationship to that from simultaneous inversion but always overestimates resolution and the inversion system using differential times has a greater ability to resolve the source region structure than the system using absolute times

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

amplitude ratio tomography for regional phase q 1 we image regional seismic phase attenuation q by extending amplitude ratio techniques which are widely used to determine average q within a sampled region to obtain laterally varying q structure using tomographic techniques the method assumes that source radiation is isotropic and that the amplitude ratios can be modeled by a two dimensional q map and relative site terms application to 2286 1 hz lg amplitudes from 816 events recorded at 35 central and east asia stations yields a misfit of 0 09 log10 units a variance reduction of 73 relative to the uniform q model that best fits the data and laterally varying q from 100 to 1000 with patterns closely following regional geology the image is resolved on average to 2 5 with resolution peaking at 1 5 in the best covered areas which is remarkable given the sparse station geometry employed the high resolution results from the dense distribution of earthquake sources and is aided by the increased confidence in source locations provided by merging catalogs from many different agencies

ml amplitude tomography in north china we have selected 10 899 m l amplitude readings from 1732 events re corded by 91 stations as reported in the annual bulletin of chinese earthquakes abce and have used tomographic imaging to estimate the lateral variations of the quality factor q0 q at 1 hz within the crust of northern china estimated q0 values vary from 115 to 715 with an average of 415 q0 values are consistent with tectonic and topographic structure in eastern china q0 is low in the active tectonic regions having many faults such as the shanxi and yinchuan grabens bohai bay and tanlu fault zone and is high in the stable ordos craton q0 values are low in several topographically low lying areas such as the north china taikang hefei jianghan subei yellow sea and songliao basins whereas it is high in mountainous and uplift regions exhibiting surface expressions of crystalline basement rocks the yinshan yanshan taihang qinlin dabie and wuyi mountains and luxi and jiaoliao uplifts quality factor estimates are also consistent with pn and sn velocity patterns high velocity values in general correspond with high q0 and low velocity values with low q0 this is consistent with a common temperature influence in the crust and uppermost mantle

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

controls on the cd isotope composition of upper cretaceous cenomanian turonian organic rich mudrocks from south texas eagle ford group abstract the isotopic composition of cd buried in marine sediments may preserve valuable palaeoenvironmental information on past ocean redox conditions or biological cycling it is unclear however how the cd isotope composition of the sedimentary record reflects these processes in this study new cd isotope data are presented along with 13c and cd mo and toc concentrations from organic rich mudrocks from the southern western interior seaway wis spanning the cenomanian turonian stages within the eagle ford group of the maverick basin texas usa relationships between cd toc 114cd and moef indicate that sedimentary cd was derived from organic matter with additional contributions from cds formed in euxinic water masses local redox conditions exerted a primary control on the 114cd composition of these deposits with high 114cd values attributed to near quantitative removal from seawater in euxinic environments lower 114cd values in non euxinic environments may reflect isotopically light cd associated with organic material due to partial remineralization these observations imply that 114cd values of samples deposited in demonstrably euxinic conditions may be used to constrain the 114cdseawater coming into the maverick basin at this time and give a composition of 0 28 0 11 2 sd for the early cenomanian samples from an interval of peak organic carbon burial globally namely oceanic anoxic event 2 oae 2 show anomalous 114cd and cd patterns compared to the rest of the data implying a perturbation to the dissolved cd pool the data presented in this study demonstrate that sedimentary cd isotopes preserve valuable information on the extent of cd burial into sulfide bearing sediments at both local and global scales

attenuation of lg in the western us using the usarray 1 the unprecedented breadth and density of the usarray allows us to resolve lateral variations of 1 hz lg attenuation to 0 5 degrees over much of the western united states we collected over 31 000 lg amplitudes from 547 events and 408 stations of the initial usarray footprint two dimensional tomographic inversion yielded q ranging from 60 to 550 with a variance reduction of 47 relative to the best fit constant q model q 155 q is low over most of the region with lowest values associated with recent volcanic activity and active shear zones high q is found in older stable crust notably the colorado and columbia plateaus while smaller islands of high q are associated with batholiths including the sierra nevada peninsular and bitterroot ranges the western mojave and okanogan highlands as well as other areas of competent crust such as the harcuvar range and two topographically bounded blocks in the basin and range

a novel technique for measuring lg attenuation results from eastern canada between 1 to 10 hz spectral amplitudes of regionally recorded lg waves are studied in detail between 0 6 and 10 hz using vertical component velocity seismograms of the eastern canada telemetered network stations and a supplementary seismic research observatory type station at glen almond gac quebec we find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest furthermore they are found to be strongly frequency dependent consequently it is essential that they be taken into consideration in studies of lg wave attenuation and lg source spectra of regionally recorded seismic events we present a new method of measuring interstation surface wave attenuation which is closely related to the conventional two station method while retaining all the desirable features of the conventional two station method the new technique which we will call the reversed two station method allows simple direct one parameter determination of the lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error the reversed two station method is successfully tested over weakly attenuating short 53 to 210 km interstation paths in eastern canada a difficult experimental condition by normal standards the lg attenuation coefficient 0 6 to 10 hz in eastern canada is found to be frequency dependent and of the form f 0 0008 f 0 81 km 1 at higher frequencies the lg attenuation appears to be essentially frequency independent this latter finding is preliminarily interpreted as evidence that regionally recorded lg waves in the canadian shield are as in the case of lg waves propagating through the structurally complex appalachian province contaminated by the high frequency coda of sn waves the lg contamination over the shield paths becomes severe starting at 14 hz twice the frequency above which the lg signal propagating over the appalachian province becomes completely dominated by non lg arrivals

lateral variations of crustal seismic attenuation along the indepth profiles in tibet from lg q inversion 1 fourier spectra of crustal guided lg waves are collected to study seismic attenuation or q along the indepth profiles the 1 hz lg q q0 values are measured between many pairs of two stations and input to a back projection algorithm to obtain laterally varying q0 models along the indepth iii profile in central tibet the q0 model consists of low and nearly constant values of 90 these low values are consistent with abnormally high temperature as well as partial melts in the crust along the indepth ii profile in southern tibet the q0 values increase southward they are extremely low 60 over the northernmost segment but increase by a factor of 2 over a distance of 100 km between the indus yalong suture and the kangmar dome farther south and into the high himalayas q0 values are higher than 300 regional rayleigh waves observed along the northern indepth ii profile are used to infer a low velocity low q layer at midcrustal depths between 15 and 30 km in southern tibet the aqueous fluid trapped in the upper crust and a midcrust partial melting zone associated with the underthrusting of the indian lithosphere are the likely causes of the high lg attenuation in southern tibet low q rather then a systematic lg conversion along a dipping moho is the main cause of the previously observed lg blockage over paths crossing the southern tibetan boundary

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

yield estimation of the 25 may 2009 north korean nuclear explosion we collect nine vertical component broadband seismograms from the 25 may 2009 north korean nuclear explosion for a regional seismic network in which eight stations also recorded the 9 october 2006 north korean nuclear test comparing the observed waveforms and spectra from the two events we estimate that the amplitudes of the records from the second event are approximately five times those from the first one additionally we use 599 vertical broadband seismograms from 82 regional events recorded on the regional network between december 1995 and may 2009 to calibrate the network lg wave magnitude the calibrated network is used to calculate the lg wave body wave magnitude m b lg 4 53 for the 25 may 2009 north korean nuclear explosion based upon 15 first arrivals from the two north korea nuclear explosions the regional pn velocity in the northeast china north korea region is calculated to be 8 0 km s this result along with the regional geological structures suggests that the north korean test site nkts is located at a relatively stable continental region we thus use a modified fully coupled magnitude yield relation to estimate the explosion yield and the result shows that the yield of the 25 may 2009 north korean nuclear test is approximately 2 35 kt under the minimum burial depth assumption online material epicentral parameters computed m b lg and corrected m b lg for 82 events used in the study

rayleigh wave multipathing along the west coast of north america we have created a movie of surface ground motion for the 3 november 2002 denali fault earthquake based on spectral element simulations using crustal model crust2 0 mantle model s20rts topography and bathymetry model etopo5 and a finite fault slip model the movie features two anomalous wave packets that travel along the west coast of the north american plate following off great circle paths these wave packets are rayleigh waves with dominant periods around 20 sec which are also found in seismograms recorded by the southern cali fornia seismic network one of these packets is the direct surface wave whose group arrival time changes laterally as dictated by the shape of the oregon coast the other packet is a surface wave reflected by a lateral interface underneath the rocky moun tains a linear reflector parallel to the canadian coast offsetting it by a few hundred kilometers can explain its arrival time but the offsetting distance derived from the synthetic seismograms puts the reflector 350 km northeast of the result obtained from the data indicating a need to update the crustal and mantle models in this area online material animation of normalized simulated vertical displacement for the 2002 denali earthquake

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

zinc and cadmium isotope evidence for redox driven perturbations to global micronutrient cycles during oceanic anoxic event 2 late cretaceous abstract this study uses organic rich sediments from the tarfaya basin morocco to assess the cd and zn isotope response to dramatic global palaeoenvironmental change during the cenomanian turonian interval late cretaceous these organic rich continental margin deposits include an expression of oceanic anoxic event 2 oae 2 94 ma an interval associated with the spread of low oxygen marine environments and widespread burial of organic rich sediments due to placement of the tarfaya basin in a region of upwelling and relatively constant local environmental conditions the stratigraphic variations in 114 cd and 66 zn values largely reflect changes in the seawater isotopic composition of the sub surface proto north atlantic ocean positive shifts of 0 2 0 3 away from background values in 114 cd and 66 zn are observed during the main phase of the positive carbon isotope excursion associated with oae 2 these isotopic shifts are coeval with decreases in cd toc and zn toc ratios and thus imply that drawdown of isotopically light cd and zn from seawater inventories was a result of extensive burial of these metals in organic rich marine sediments globally low 66 zn values during the plenus cold event a cooler episode during oae 2 are similar in timing and magnitude to variations found in the english chalk eastbourne uk and support the inference of a global control on these isotopic excursions the 66 zn values during the plenus cold event are taken to record global oxygenation possibly including the remobilization of isotopically light zn from continental margin sediments a considerably smaller change in 114 cd values for this interval implies that the cd and zn isotope systems can provide information about slightly different environmental processes with global seawater composition with respect to zn also being influenced by the magnitude of oxic removal sinks and isotopically light zn input fluxes from sediments and hydrothermal fluids

joint inversion of receiver functions and surface waves with enhanced preconditioning on densely distributed cndsn stations crustal and upper mantle structure beneath china we present shear wave velocity structure beneath china by joint modeling of teleseismic receiver function and rayleigh wave group velocity dispersion data observed at 1000 permanent broadband seismic stations in the chinese national digital seismic network cndsn a ray parameter based stacking method is employed to minimize artifacts in stacking receiver functions from different sources the rayleigh wave dispersion curve is extracted from group velocity tomographic models at all applicable periods enhanced preconditions are applied on the linearized iterative inversion to regularize and balance multiple types of data the velocity profile inversion at each station starts from an initial model derived from sediments crustal thickness vp vs ratio and pn sn models this multistep approach not only reduces uncertainty and nonuniqueness of the velocity inversion but also efficiently fills information gap in each data set we then generate a 3 d s velocity model by combining and smoothing all the 1 d models the obtained 3 d model reveals crustal and upper mantle velocity structures that are well correlated with tectonic features of china for example our model shows a clear east west bimodal distribution at 35 km deep low velocity in the crust beneath central and eastern tibetan plateau and sedimentary structure in major cratons and basins our model is consistent with existing tomographic models in large scale but provides more structural details in regional and local scales

pgq model for nepal himalaya abstract we investigate the spatial variations of pg attenuation structure in nepal himalaya we implement the two station method on 2325 waveforms obtained from 435 events recorded at 151 stations deployed across nepal himalaya to measure the pg wave quality factor q these station station measurements are inverted further for investigating the spatial variations of pg attenuation using a back projection algorithm the model contains variations across the region with much of the region being dominated by high attenuation it is observed that the areas around the existing faults and lineaments exhibit very low q values a few exceptional high q pockets are observed to be limited predominantly in the north western side of our study area we hypothesize that intrinsic attenuation plays a major role in causing the high apparent pg attenuation in the crust of nepal himalaya this may be mainly caused by highly pressurized fluids trapped within a thin low velocity layer lvl at shallow depths moreover it is interesting to observe that all the past earthquakes of m w 7 since 1934 fall into the regions of low q values but not the lowest it may be anticipated that the very low q areas are too weak to sustain the accumulation of high energy release during a large magnitude earthquake therefore the observed low q structures across the study area may imply a weak crust and subsequently a favorable zone for future rupture

bioevents and redox conditions around the cenomanian turonian anoxic event in central mexico abstract the xilitla section of central mexico western margin of the proto north atlantic is characterized by pelagic sediments enriched in marine organic matter using biostratigraphic and radiometric data it was dated at the latest cenomanian earliest turonian transition we identified an interval coeval with the faunal turnover associated with the oceanic anoxic event 2 oae 2 recording the heterohelix shift and the filament event for the first time in mexico an integral analysis of sedimentary facies pyrite and geochemical proxies reveals vertically variable redox conditions with prevailing anoxic to dysoxic bottom waters along with phosphorous and manganese depletion the highest content of total organic carbon and of certain redox sensitive trace elements rstes is found during part of the anoxic event confirming more uniform and constant oxygen depleted conditions this interval is also characterized by a significant enrichment in biogenic barium and elevated toc ntot ratios suggesting a link between productivity and anoxia sulfur isotope fractionation has a maximum value within the anoxic event favored by the increase in the flux of organic matter and intensified through sulfur recycling highly bioturbated beds representing short lived episodes of oxic conditions are intermittent within the oae 2 and become more frequent in the early turonian this study proposes a model similar to that of modern upwelling regions high marine productivity controlled organic matter burial and oxygenation at the seafloor varying between anoxic laminated facies with small pyrite framboids and dysoxic conditions bedding parallel bioturbated facies with inoceramid bivalves and large pyrite framboids interrupted by short term well oxygenated episodes thoroughly bioturbated facies with common benthic foraminifera general low oxygen conditions led to the formation of glauconite and pyrite bacterially mediated the enrichment of redox sensitive trace elements in sediments cd zn v and cr scavenged by organic matter and ni mo pb co and re by pyrite and resulted in mn and p depletion

elemental abundance anomalies in the late cenomanian extinction interval a search for the source s elemental abundances have been measured by neutron activation methods across the cenomanian turonian late cretaceous extinction interval in samples collected from sixteen sites in the western interior basin of north america and from twelve widely separated locations around the globe including six odp dsdp sites in most western interior basin sites in colombia and in western europe weaker two closely spaced elemental abundance peaks occur in the upper cenomanian 92 m y spanning the ammonite zones ofsciponoceras gracile throughneocardioceras juddii elements with anomalously high concentrations include sc ti v cr mn co ni ir pt and au the lower peak coincides with the disappearance extinction of the foraminiferrotalipora cushmani in north american sectionsr greenhornensis also disappears at or just below this horizon but in europe it disappears considerably earlier thanr cushmani a series of molluscan extinction and speciation or migration events also begins near the stratigraphic level of the lower elemental abundance peak the well documented positive 13c excursion begins just before the extinctions and the elemental anomalies and continues into the lower turonian well above the upper anomaly this carbon isotope excursion has been observed in east european sections where we find little or no evidence of the elemental anomalies suggesting that the two phenomena may not be tightly coupled elemental abundance ratios in the anomalies closely resemble those of mid atlantic ridge basalt or hawaiian lava tholeiitic but not those of c1 chondrite black shale average crustal rocks or lamproite and kimberlite of roughly similar age in southeastern kansas the excess ir and other siderophiles hint at possible large body impact s for the source however we have not located microspherules other than biogenic calcispheres or shocked mineral grains in any of our samples furthermore sc ti v and mn are not enriched in differentiated solar system bodies although the weak geochemical signal from comet impact s could be masked by the strong terrestrial like overprint these anomalies more likely resulted either from intense seafloor spreading activity or merely from increased circulation of deep metal rich water associated with the large late cenomanian through early turonian eustatic rise and deep water opening of the south atlantic the flooding of continental seaways and margins also could have contributed to the anomalies by preventing much continental detritus from diluting the normal background marine geochemical component

strong lg wave attenuation in the middle east continental collision orogenic belt abstract using lg wave q tomography we construct a broadband crustal attenuation model for the middle east the q lg images reveal a relationship between attenuation and geological structures strong attenuation is found in the continental collision orogenic belt that extends from the turkish and iranian plateau to the pamir plateau we investigate the frequency dependence of q lg in different geologic formations the results illustrate that q lg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions an average q lg value between 0 2 and 2 0 hz q lg 0 2 2 0 hz may be a critical index for crustal attenuation and is used to infer the regional geology low q lg anomalies are present in the eastern turkish plateau and correlate well with low pn velocities and cenozoic volcanic activity thus indicating possible partial melting within the crust in this region very strong attenuation is also observed in central iran the afghanistan block and the southern caspian sea this in line with the previously observed high crustal temperature high conductivity layers and thick marine sediments in these areas suggests the high lg attenuation is caused by abnormally high tectonic and thermal activities

resolution uncertainty and whole earth tomography 1 using the arrival times of 10 distinct phases from the international seismological center catalogue p s pp pcp ss scs pkpab pkpbc pkpdf sksac and two sets of differential times ss s410s and ss s660s we estimate the p and s velocity structure of the whole earth mantle outer core and inner core boundary topography of four interfaces within the earth hypocentral relocation parameters and station corrections the entire catalogue is relocated and reassociated using the radial velocity model ak135 both p and s phases are used in the relocation of over 41 000 events in depth isotropic velocity variations within the earth are parameterized by 22 layers lateral variations in shear and compressional velocity within the layers are represented by one of two grids in the mantle each layer is subdivided into 4560 equal volume cells of dimension 3 3 at the equator however in the outer and inner core the cell size is increased to 6 6 this change in grid spacing accounts for decreasing cell volumes with depth and variations in sampling between the mantle and core previous attempts using a fine grid throughout the earth resulted in poor resolution of core structure with the current grid the resolution of velocity heterogeneity in the mantle and outer core is comparable in the upper and midmantle the well resolved cells lie beneath eurasia and a narrow zone surrounding the mantle beneath the pacific basin in the lowest mantle the resolution decreases significantly an examination of the averaging kernels associated with six locations near the base of the mantle reveals the significant lateral and vertical averaging inherent in estimates of compressional velocity in well sampled regions of the outer core we are able to resolve compressional velocity variations in our 6 6 cells however velocity variations in the inner core are poorly constrained at the scale of our blocks in well sampled regions of the mantle and outer core model parameter standard deviations remain below 0 25 for much of the inner core the standard deviations are quite large exceeding 0 5 narrow high velocity anomalies are imaged in the upper mantle associated with subduction zones in a number of locations such as beneath the americas these features extend well into the lower mantle in the outer core heterogeneity is generally lower in magnitude of the order of 0 5 the most notable feature in the outer core is a systematic shift to slightly higher velocity in addition we find a roughly symmetric distribution of heterogeneity at the base of the outer core compressional velocities are generally higher in the equatorial regions and lower at the poles

crustal attenuation within the turkish plateau and surrounding regions the lateral variations of seismic attenuation in the crust of turkey and surrounding regions have been imaged from the inversion of interstation lg q measurements this study develops the first tomographic model for lg q 0 in this region that model is consistent with previous more qualitative lg attenuation models that showed inefficient or blocked lg across the eurasian arabian plate boundary in general the northern arabian platform has low to normal lg q 0 values 250 350 whereas high q 0 values 670 800 occur in the southern arabian plate additionally we have found a dramatic decrease in lg q 0 across the bitlis suture the plate boundary between the arabian and eurasian plates beneath the turkish plateau our high to moderate lg attenuation values q 0 100 200 probably originates from both scattering and intrinsic attenuation due to the tectonic complexity and the widespread young volcanics in the region we conclude that the lowest q 0 values for the east anatolian plateau 70 100 and the portion of western turkey around the menderes massif 60 150 are probably caused by intrinsic attenuation we find low to normal lg q 0 values 150 300 beneath the part of the taurus mountains in western anatolia these higher values may be related to the nature of the crust in the tauride mountain belt we also mapped the lateral variations in lg and observed a fairly consistent negative correlation between and lg q 0 in the northern middle east

a statistical model for ground motion produced by earthquakes at local and regional distances to adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models we constrain the parameters of duration geometrical spreading and spectral shape by modeling the main ground motion as being the result of major contributions by the direct s wave and supercritically reflected s waves the results of our modeling are constrained to be consistent with values from full wave synthetics for the test models the combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements velocities and accelerations of the 1982 miramichi earthquakes in new brunswick canada in addition upon considering the effects of source depth and crustal structure for the november 25 1988 saguenay earthquake m 5 8 in quebec canada the predicted mean peak horizontal ground accelerations match the observed data very well the effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges

organic geochemistry of the eagle ford group in texas a comprehensive regional organic geochemical study was performed on outcrop and core samples from the eagle ford group with the aim of determining variations in organic matter source thermal maturity and depositional environments total organic carbon toc and rock eval pyrolysis parameters show that the eagle ford group has excellent hydrocarbon source rock potential and is dominated by type ii kerogen distributions of regular steranes hopanes and monoaromatic steroids confirm a marine carbonate depositional environment aryl isoprenoid ratios suggest the occurrence of intermittent photic zone anoxia the n alkane and sterane distributions and the presence of pregnanes homopregnanes and gammacerane suggest deposition under hypersaline conditions particularly in west and east texas in east texas biomarkers indicate that the eagle ford group was partially sourced from terrigenous organic matter and deposited under oxic suboxic conditions thermal maturity parameters including the temperature at which the peak corresponding to the compounds produced from the thermal degradation of kerogen in the rock eval chromatogram maximizes tmax vitrinite reflectance and biomarker ratios indicate that in west and central texas the eagle ford group is immature to marginally mature in southwest texas it is in the oil to dry gas window and in east texas the eagle ford is in the main stage of oil generation geochemical logs of biomarker ratios show that the lower eagle ford formation has the highest toc and hydrogen index particularly in the lozier canyon member experienced stronger anoxic conditions during deposition and has lower clay content compared with the upper eagle ford formation geochemical parameters show that the latter may have received an additional siliciclastic and terrigenous organic matter input under oxic dysoxic conditions isotope data indicate a marine organic matter source for the eagle ford group but surprisingly 13c values do not show significant organic facies depositional environment or thermal maturity variations

the mid cretaceous north atlantic nutrient trap black shales and oaes organic rich sediments are the salient marine sedimentation product in the mid cretaceous of the ocean basins formed in the mesozoic oceanic anoxic events oaes are discrete and particularly organic rich intervals within these mid cretaceous organic rich sequences and are defined by pronounced carbon isotope excursions marine productivity during oaes appears to have been enhanced by the increased availability of biolimiting nutrients in seawater due to hydrothermal alteration of submarine basalts in the pacific and proto indian oceans the exact mechanisms behind the deposition of organic rich sediments in the mid cretaceous are still a matter of discussion but a hypothesis which is often put forward is that their deposition was a consequence of the coupling of a particular paleogeography with changes in ocean circulation and nutrient supply in this study we used a global coupled climate model to investigate oceanic processes that affect the interbasinal exchange of nutrients as well as their spatial distribution and bioavailability we conclude that the mid cretaceous north atlantic was a nutrient trap as a consequence of an estuarine circulation with respect to the pacific organic rich sediments in the north atlantic were deposited below regions of intense upwelling we suggest that enhanced productivity during oaes was a consequence of upwelling of pacific derived nutrient rich seawater associated with submarine igneous events