Isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates (Miocene, Great Bahama Bank)     

Tracy D. Frank  & Karin Bernet 《Sedimentology》2000,47(6):1119-1134

The stable isotope geochemistry of Miocene sediments from the leeward margin of the Great Bahama Bank was examined to investigate burial diagenetic processes in periplatform carbonates. Data indicate that, in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope, rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined. The present study focuses on Ocean Drilling Program Sites 1006 and 1007, the most distal of five sites drilled from marginal to deep basin environments during Leg 166. These Miocene sections are characterized by their cyclic appearance, manifest as decimetre‐ to metre‐scale alternations between light‐coloured ooze/chalk/limestone and dark‐coloured marl/marlstone. The section at Site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of ～675 m. Fluctuations in δ¹⁸O and δ¹³C values at this site are independent of lithological variation and reflect primary conditions. At Site 1007, located at the toe‐of‐slope and composed of a mixture of bank‐derived and pelagic carbonate, limestones are densely cemented, show little evidence of compaction and have δ¹⁸O values up to 2‰ higher than coeval sediments at Site 1006. Marlstones at Site 1007 are poorly cemented, exhibit an increase in compaction‐related features with depth and have lower and more variable δ¹⁸O values that are similar to those of coeval sediments at Site 1006. Isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first ～100 m of burial. Higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones; in spite of significant compaction and pressure solution during burial, original isotopic compositions appear to be best preserved in these intervals at Site 1007. The documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of considering such factors when interpreting geochemical data from ancient shelf and slope limestones.  相似文献   

The 2013 European Seismic Hazard Model: key components and results   总被引：11，自引：5，他引：6  

Jochen Woessner  Danciu Laurentiu  Domenico Giardini  Helen Crowley  Fabrice Cotton  Gottfried Grünthal  Gianluca Valensise  Ronald Arvidsson  Roberto Basili  Mine Betül Demircioglu  Stefan Hiemer  Carlo Meletti  Roger W. Musson  Andrea N. Rovida  Karin Sesetyan  Massimiliano Stucchi  The SHARE Consortium 《Bulletin of Earthquake Engineering》2015,13(12):3553-3596

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Ice-margin retreat and grounding-zone dynamics during initial deglaciation of the Storfjordrenna Ice Stream,western Barents Sea     

Calvin S. Shackleton  Monica C. M. Winsborrow  Karin Andreassen  Renata G. Lucchi  Lilja R. Bjarnadóttir 《Boreas: An International Journal of Quaternary Research》2020,49(1):38-51

Processes occurring at the grounding zone of marine terminating ice streams are crucial to marginal stability, influencing ice discharge over the grounding-line, and thereby regulating ice-sheet mass balance. We present new marine geophysical data sets over a ~30×40 km area from a former ice-stream grounding zone in Storfjordrenna, a large cross-shelf trough in the western Barents Sea, south of Svalbard. Mapped ice-marginal landforms on the outer shelf include a large accumulation of grounding-zone deposits and a diverse population of iceberg ploughmarks. Published minimum ages of deglaciation in this region indicate that the deposits relate to the deglaciation of the Late Weichselian Storfjordrenna Ice Stream, a major outlet of the Barents Sea–Svalbard Ice Sheet. Sea-floor geomorphology records initial ice-stream retreat from the continental shelf break, and subsequent stabilization of the ice margin in outer-Storfjordrenna. Clustering of distinct iceberg ploughmark sets suggests locally diverse controls on iceberg calving, producing multi-keeled, tabular icebergs at the southern sector of the former ice margin, and deep-drafted, single-keeled icebergs in the northern sector. Retreat of the palaeo-ice stream from the continental shelf break was characterized by ice-margin break-up via large calving events, evidenced by intensive iceberg scouring on the outer shelf. The retreating ice margin stabilized in outer-Storfjordrenna, where the southern tip of Spitsbergen and underlying bedrock ridges provide lateral and basal pinning points. Ice-proximal fans on the western flank of the grounding-zone deposits document subglacial meltwater conduit and meltwater plume activity at the ice margin during deglaciation. Along the length of the former ice margin, key environmental parameters probably impacted ice-margin stability and grounding-zone deposition, and should be taken into consideration when reconstructing recent changes or predicting future changes to the margins of modern ice streams.  相似文献   

A probabilistic seismic hazard assessment for the Turkish territory: part II—fault source and background seismicity model     

Mine Betül Demircioğlu  Karin Şeşetyan  Tamer Y. Duman  Tolga Çan  Senem Tekin  Semih Ergintav 《Bulletin of Earthquake Engineering》2018,16(8):3399-3438

Over the years, several local and regional seismic hazard studies have been conducted for the estimation of the seismic hazard in Turkey using different statistical processing tools for instrumental and historical earthquake data and modeling the geologic and tectonic characteristics of the region. Recently developed techniques, increased knowledge and improved databases brought the necessity to review the national active fault database and the compiled earthquake catalogue for the development of a national earthquake hazard map. A national earthquake strategy and action plan were conceived and accordingly with the collaboration of the several institutions and expert researchers, the Revision of Turkish Seismic Hazard Map Project (UDAP-Ç-13-06) was initiated, and finalized at the end of 2014. The scope of the project was confined to the revision of current national seismic hazard map, using the state of the art technologies and knowledge of the active fault, earthquake database, and ground motion prediction equations. The following two seismic source zonation models are developed for the probabilistic earthquake hazard analysis: (1) Area source model, (2) Fault and spatial smoothing seismic source model (FSBCK). In this study, we focus on the development and the characterization of the Fault Source model, the background spatially smoothed seismicity model and intrinsic uncertainty on the earthquake occurrence-rates-estimation. Finally, PSHA results obtained from the fault and spatial smoothed seismic source model are presented for 43, 72, 475 and 2475 years return periods (corresponding to 69, 50, 10, and 2% probability of exceedance in 50 years) for PGA and 5% damped spectral accelerations at 0.2 and 1.0 s.  相似文献   

Seismic hazard map of the Middle East     

Domenico Giardini  Laurentiu Danciu  Mustafa Erdik  Karin Şeşetyan  Mine B. Demircioğlu Tümsa  Sinan Akkar  Levent Gülen  Mehdi Zare 《Bulletin of Earthquake Engineering》2018,16(8):3567-3570

The collaborative project Earthquake Model of the Middle East (EMME, 2010–2015) brought together scientists and engineers from the leading research institutions in the region and delivered state-of-the-art seismic hazard assessment covering Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Iraq, Jordan, Lebanon, Palestine, Pakistan, Syria and Turkey. Their efforts have been materialized in the first homogenized seismic hazard model comprising earthquake catalogues, mapped active faults, strong motions databank, ground motion models and the estimated ground motion values for various intensity measure types and relevant return periods (e.g. 475–5000 years). The reference seismic hazard map of the Middle East, depicts the mean values of peak ground acceleration with a 10% chance of exceedance in 50 years, corresponding to a mean return period of 475 years. A full resolution poster is provided with this contribution.  相似文献   

Land-use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments     

Heleen A. de Wit  Ahti Lepistö  Hannu Marttila  Hannah Wenng  Marianne Bechmann  Gitte Blicher-Mathiesen  Karin Eklöf  Martyn N. Futter  Pirkko Kortelainen  Brian Kronvang  Katarina Kyllmar  Jelena Rakovic 《水文研究》2020,34(25):4831-4850

Agricultural, forestry-impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry-impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (−15 μg totN L⁻¹ year⁻¹) and natural (−0.4 μg NO₃-N L⁻¹ year⁻¹) catchments, but individual sites displayed few long-term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry-impacted sites had a significant decline in totP (−0.1 μg P L⁻¹ year⁻¹). A small but significant increase in totP fluxes (+0.4 kg P km⁻² year⁻¹) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large-scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs.  相似文献   

Petrography and geochemistry of the impact to postimpact transition layer at the El'gygytgyn impact structure in Chukotka,Arctic Russia     

Karin Maierhofer  Christian Koeberl  Julie Brigham‐Grette 《Meteoritics & planetary science》2019,54(10):2510-2531

The 3.6 Ma El'gygytgyn impact structure, located in northeast Chukotka in Arctic Russia, was largely formed in acidic volcanic rocks. The 18 km diameter circular depression is today filled with Lake El'gygytgyn (diameter of 12 km) that contains a continuous record of lacustrine sediments of the Arctic from the past 3.6 Myr. In 2009, El'gygytgyn became the focus of the International Continental Scientific Drilling Program (ICDP) in which a total of 642.4 m of drill core was recovered. Lithostratigraphically, the drill cores comprise lacustrine sediment sequences, impact breccias, and deformed target rocks. The impactite core was recovered from 316.08 to 517.30 meters below lake floor (mblf). Because of the rare, outstanding recovery, the transition zone, ranging from 311.47 to 317.38 m, between the postimpact lacustrine sediments and the impactite sequences, was studied petrographically and geochemically. The transition layer comprises a mixture of about 6 m of loose sedimentary and volcanic material containing isolated clasts of minerals and melt. Shock metamorphic effects, such as planar fractures (PFs) and planar deformation features (PDFs), were observed in a few quartz grains. The discoveries of silica diaplectic glass hosting coesite, kinked micas and amphibole, lechatelierite, numerous impact melt shards and clasts, and spherules are associated with the impact event. The occurrence of spherules, impact melt clasts, silica diaplectic glass, and lechatelierite, about 1 m below the onset of the transition, marks the beginning of the more coherent impact ejecta layer. The results of siderophile interelement ratios of the transition layer spherules give indications of the relative contribution of the meteoritical component.  相似文献   

Application of a mass-balance model to predict PCDD/F turnover in a Baltic coastal estuary     

O. Magnus Karlsson  J. Mikael Malmaeus  Sarah Josefsson  Karin Wiberg  Lars Håkanson 《Estuarine, Coastal and Shelf Science》2010

A dynamical, process-based mass-balance model was applied to quantify the transports of polychlorinated-p-dibenzodioxins and dibenzofurans (PCDD/Fs) to, within and from the Kallrigafjärden Bay, a coastal estuary in the Baltic Sea, and to predict the PCDD/F levels in the water and sediments of the bay. Before the modelling, a one-year sampling programme was implemented in 2007–2008 to measure the flows of PCDD/Fs in tributaries entering the system, the fluxes from the adjacent sea and the levels in water, sediment and fish within the estuary. The collected data set was used as input data to the model and for validation purposes.  相似文献   

Submarine Lateglacial lake deposits from the Kattegat,southern Scandinavia     

Peter Wiberg‐Larsen  Ole Bennike  Jrn Bo Jensen 《第四纪科学杂志》2019,34(2):165-171

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Teleconnections of the tropical Atlantic and Pacific Oceans in a CMIP5 model ensemble     

Irena Ott  Karin Romberg  Jucundus Jacobeit 《Climate Dynamics》2015,44(11-12):3043-3055

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