The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model

Despite the gently dipping slopes (ca 1°), large-scale submarine slope failures have occurred on the mid-Norwegian continental margin (Storegga, Sklinnadjupet, Traenadjupet), suggesting the presence of special conditions predisposing to failure in this formerly glaciated margin. With a volume estimated between 2,400 and 3,200 km³ and an affected area of approximately 95,000 km², the Storegga slide represents one of the largest and best-studied submarine slides of Holocene age known worldwide. Finite element modeling of slope failure indicates that a large (6.5 < Ms < 7.0) seismic triggering mechanism would not be sufficient to cause failure at more than 110 m below the seabed as observed for the slip planes at Storegga (northern sidewall). This implies that other factors (e.g., liquefaction, strain softening, gas charging, rapid burial) are needed to explain the occurrence of the Storegga slide with a deep surface of failure. In this paper, we discuss the importance of the compaction effect of rapidly accumulated sediments in the slide area. During compaction, sediment grains reorganize themselves, thereby, expelling pore water. Consequently, depending on sedimentation rate and permeability, excess pore pressures might result beneath less permeable sediments. Our modeling and cross-checking illustrate how excess pore pressure generation due to high sedimentation rate could explain the development of layers of weakness, and thus, how such a large slide might have been initiated in deep sediments. Using the highest sedimentation rate estimated in the area (36 and 27 m/kyr between 16.2 and 15 kyr BP), 1D modeling shows excess pore pressure values of around 200 kPa at a depth of 100 m below the seafloor 15 kyr BP and 60 kPa at a depth of 100 m at the time of the slide (8 kyr BP). Excess pore pressure apparently drastically reduced the resistance of the sediment (incomplete consolidation). In addition, 2D modeling shows that permeability anisotropies can significantly affect the lateral extent of excess pore pressure dissipation, affecting, that way, normally consolidated sediments far from the excess pore pressure initiation area.     

Book Reviews

Book reviewed in this article:
Petroleum Economics and Offshore Mining Legislation. A. P. H. VAN M eurs.
Sedimentografia-Atlante fotografico delle Strutture Primarie dei Sedimenti. F ranco R icci L ucchi.
Le Dolomiti. Geologia dei Monti tra Isarco e Piave. P. L eonardi.
Sedimente und Sedimentgesteine (Sediments and Sedimentary Rocks). H. F ücht-bauer and G erman M üller.
Geochronology of Phanerozoic Orogenic Belts—Eclogae Geol. Helv. , 63(1). E. J äger , M. G rünenfelder and R. H erb (Editors).
Physical Processes of Sedimentation. J. R. L. A llen .
African Magmatism and Tectonics. T. N. C lifford and I. G. G ass (Editors).
Les Formations sèdimentaires tertiaires et quaternaires de la Cuvette tchadienne et les Sols qui en dèrivent (Mèm. O.R.S.T.O.M. , 43). J. P ias.
Flysch Sedimentology in Northern America. J. L ajoie (Editor).
Development of the Northern Apennines Geosyncline. G. S estini (Editor).
Ancient Sedimentary Environments. richard C. selley.
Introductory Petrography of Fossils. A S. horowitz and P. E. potter     

Book reviews

Book review in this article
Cross-bedding, Bedforms and Paleocurrents, by D. M. Rubin
Beach and Nearshore Sediments and Processes, ed. By R. A. Davis Jr.,
Sedimentary Processes on the Amazon Continental Shelf, ed. by C. A. Nittrouer and D. J. DeMaster
Fjords: Processes and Products, by J. P. M. Syvitski, D. C. Burrell, and J. M. Skei
Alluvial Soils, ed. by J. Gerrard,
Electron Micrographs (TEM, SEM) of Clays and Clay Minerals, by K.-H. Henning and M. Störr
The Origins of Angiosperms and their Biological consequences, ed. by E. M. Friis, W. G. Chaloner & P. R. Crane
The Motion of Allochthonous Terranes Across the North Pacific Basin, by M. G. Debiche, A. Cox and D. Engebretson
Geomorphic Systems of North America, ed. by W. L. Graf
Approaches to Interpretation of Sedimentary Environments, ed. by D. J. Cant and F. J. Hein
Carbonate Depositional Environments: Modern and Ancient. Part I. Reefs.
European Dinantian Environments, ed. by J. Miller, A.E. Adams, and V.P. Wright
Mesozoic and Cenozoic Oceans, ed. by K. J. Hsü
Marine Minerals: Advances in Research and Resource Assessment, ed. by P.G. Teleki, M.R. Dobson, J.R. Moore and U. von Stackelberg.
Sedimentation and Mineral Deposits in the Southwestern Pacific Ocean, ed. by D.S. Cronan
A Practical Approach to Sedimentology, by Ray Lindholm
Clastic Particles, Scanning Electron Microscopy and Shape Analysis of Sedimentary and Volcanic Claste, ed. by John R. Marshall     

Book reviews

Book review in this article
Phosphate Deposits of the World; Volume 2, Phosphate Rock Resources, ed. by A. J. G. Notholt, R.P. Sheldon and D.F. Davidson
Sedimentology and Petroleum Geology, by Knut Bjørlykke
Nonmetalliferous Stratabound Ore Fields, ed. by M. K. de Brodtkorb
Clay Sedimentology, by H. Chamley
Paleoclimatology and Paleometeorology: Modern and Past Patterns of Global Atmospheric Transport, ed. by M. Leinen and M. Sarnthein
Geology of North America—An Overview, ed. by A. W. Bally and A. R. Palmer
Nearshore Sediment Transport, ed. by R. J. Seymour
Sedimentological Consequences of Convulsive Geological Events, ed. by H. E. Clifton
Sea-Level Changes: An Integrated Approach, ed. by C. K. Wilgus, B. S. Hastings, C. G. St C. Kendall, H. W. Posamentier, C. Ross and C. Van Wagoner     

Book Reviews

Book reviewed in this article:
Ground Wcter Problems . E. E riksson , Y. G ustafson and K. N ilsson (Editors).
Geochemie der Sedimente . E. T. D egens .
Current Ripples—Their Relation to Patterns of Water and Sediment Motion . J. R. L. A llen .
"Meteor" Forschtrngsergebnisse, Reihe C, 1. GeoIogie und Geophysik . E. S eibold und H. C loss
Tertiary Sea-Level Fluctuations . W. F. T anner (Editor).
Amphibotes . W. G . E rnst .
Introduction to Paleolimnology — Developments in Sedimentology , 11. C.C. R eeves J r.     

Book Review

Principles of Lithogenesis, 2. , N. M. STRAKHOV (English translation by J. PAUL FITZSIMMONS, edited by S. I. TOMKIEFF and J. S. HEMINGWAY).
The New Concepts of Continental Margin Sedimentation-A.G.I. Short Course Lecture Notes, Philadelphia, 7–9 November, 1969. D. J. STANLEY (Convener); J. R. CURRAY, G. V. MIDDLETON, D. J. STANLEY, and D. J. P. SWIFT (Lecturers).
Manual of Sedimentary Structures. C. E. B. CONYBEARE and K. A. W. CROOK.
Methods for the Study of Sedimentary Structures. ARNOLD H. BOUMA.     

Late Pleistocene and Holocene paleoseismology of an intraplate seismic zone in a large alluvial valley, the New Madrid seismic zone, Central USA

The New Madrid seismic zone (NMSZ) is an intraplate right-lateral strike-slip and thrust fault system contained mostly within the Mississippi Alluvial Valley. The most recent earthquake sequence in the zone occurred in 1811–1812 and had estimated moment magnitudes of 7–8 (e.g., [Johnston, A.C., 1996. Seismic moment assessment of stable continental earthquakes, Part 3: 1811–1812 New Madrid, 1886 Charleston, and 1755 Lisbon. Geophysical Journal International 126, 314–344; Johnston, A.C., Schweig III, E.S, 1996. The enigma of the New Madrid earthquakes of 1811–1812. Annual Reviews of Earth and Planetary Sciences 24, 339–384; Hough, S.E., Armbruster, J.G., Seeber, L., Hough, J.F., 2000. On the modified Mercalli intensities and magnitudes of the New Madrid earthquakes. Journal of Geophysical Research 105 (B10), 23,839–23,864; Tuttle, M.P., 2001. The use of liquefaction features in paleoseismology: Lessons learned in the New Madrid seismic zone, central United States. Journal of Seismology 5, 361–380]). Four earlier prehistoric earthquakes or earthquake sequences have been dated A.D. 1450 ± 150, 900 ± 100, 300 ± 200, and 2350 B.C. ± 200 years using paleoliquefaction features, particularly those associated with native American artifacts, and in some cases surface deformation ([Craven, J. A. 1995. Paleoseismology study in the New Madrid seismic zone using geological and archeological features to constrain ages of liquefaction deposits. M.S thesis, University of Memphis, Memphis, TN, U.S.A.; Tuttle, M.P., Lafferty III, R.H., Guccione, M.J., Schweig III, E.S., Lopinot, N., Cande, R., Dyer-Williams, K., Haynes, M., 1996. Use of archaeology to date liquefaction features and seismic events in the New Madrid seismic zone, central United States. Geoarchaeology 11, 451–480; Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43(2002), 313–349; Tuttle, M.P., Schweig, E.S., Sims, J.D., Lafferty, R.H., Wolf, L.W., Haynes, M.L., 2002. The earthquake potential of the New Madrid seismic zone, Bulletin of the Seismological Society of America, v 92, n. 6, p. 2080–2089; Tuttle, M.P., Schweig III, E.S., Campbell, J., Thomas, P.M., Sims, J.D., Lafferty III, R.H., 2005. Evidence for New Madrid earthquakes in A.D. 300 and 2350 B.C. Seismological Research Letters 76, 489–501]). The two most recent prehistoric and the 2350 B.C. events were probably also earthquake sequences with approximately the same magnitude as the historic sequence.Surface deformation (faulting and folding) in an alluvial setting provides many examples of stream response to gradient changes that can also be used to date past earthquake events. Stream responses include changes in channel morphology, deviations in the channel path from the regional gradient, changes in the direction of flow, anomalous longitudinal profiles, and aggradation or incision of the channel ([Merritts, D., Hesterberg, T, 1994. Stream networks and long-term surface uplift in the New Madrid seismic zone. Science 265, 1081–1084.; Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43 (2002), 313–349]). Uplift or depression of the floodplain affects the frequency of flooding and thus the thickness and style of vertical accretion or drowning of a meander scar to form a lake. Vegetation may experience trauma, mortality, and in some cases growth enhancement due to ground failure during the earthquake and hydrologic changes after the earthquake ([VanArdale, R.B., Stahle, D.W., Cleaveland, M.K., Guccione, M.J., 1998. Earthquake signals in tree-ring data from the New Madrid seismic zone and implications for paleoseismicity. Geology 26, 515–518]). Identification and dating these physical and biologic responses allows source areas to be identified and seismic events to be dated.Seven fault segments are recognized by microseismicity and geomorphology. Surface faulting has been recognized at three of these segments, Reelfoot fault, New Madrid North fault, and Bootheel fault. The Reelfoot fault is a compressive stepover along the strike-slip fault and has up to 11 m of surface relief ([Carlson, S.D., 2000. Formation and geomorphic history of Reelfoot Lake: insight into the New Madrid seismic zone. M.S. Thesis, University of Arkansas, Fayetteville, Arkansas, U.S.A]) deforming abandoned and active Mississippi River channels ([Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43 (2002), 313–349]). The New Madrid North fault apparently has only strike-slip motion and is recognized by modern microseismicity, geomorphic anomalies, and sand cataclasis ([Baldwin, J.N., Barron A.D., Kelson, K.I., Harris, J.B., Cashman, S., 2002. Preliminary paleoseismic and geophysical investigation of the North Farrenburg lineament: primary tectonic deformation associated with the New Madrid North Fault?. Seismological Research Letters 73, 393–413]). The Bootheel fault, which is not identified by the modern microseismicity, is associated with extensive liquefaction and offset channels ([Guccione, M.J., Marple, R., Autin, W.J., 2005, Evidence for Holocene displacements on the Bootheel fault (lineament) in southeastern Missouri: Seismotectonic implications for the New Madrid region. Geological Society of America Bulletin 117, 319–333]). The fault has dominantly strike-slip motion but also has a vertical component of slip. Other recognized surface deformation includes relatively low-relief folding at Big Lake/Manila high ([Guccione, M.J., VanArdale, R.B., Hehr, L.H., 2000. Origin and age of the Manila high and associated Big Lake “Sunklands”, New Madrid seismic zone, northeastern Arkansas. Geological Society of America Bulletin 112, 579–590]) and Lake St. Francis/Marked Tree high ([Guccione, M.J., VanArsdale, R.B., 1995. Origin and age of the St. Francis Sunklands using drainage patterns and sedimentology. Final report submitted to the U. S. Geological Survey, Award Number 1434-93-G-2354, Washington D.C.]), both along the subsurface Blytheville arch. Deformation at each of the fault segments does not occur during each earthquake event, indicating that earthquake sources have varied throughout the Holocene.     

Borehole image analysis of the Nankai Accretionary Wedge, ODP Leg 196: Structural and stress studies

Electrical images recorded with Resistivity-At-Bit (RAB) from two sites drilled during Ocean Drilling Program (ODP) Leg 196 were analyzed to study the effects of subduction at the Nankai margin. For the first time in the history of scientific deep-sea drilling in ODP, in situ complete borehole images of the décollement zone were obtained. Analyses of all drilling-induced fracture data indicated that the maximum horizontal compressive stress (S_Hmax) axes have an azimuth of 303°, and analyses of breakout data from RAB images indicated an azimuth of 310°. These azimuths approximate the convergence direction of the Philippine Sea plate towards the Eurasian plate. The frontal thrust at Site 808 was encountered at about 389 mbsf. Density, porosity, resistivity, and gamma ray data change across the frontal thrust. The décollement zone at the deformation front was identified between 937 and 965 mbsf. The base of the décollement is sharply defined as the maximum extent of conductive fracturing and is marked by abrupt changes in physical properties [Mikada, H., Becker, K., Moore, J.C., Klaus, A., Austin, G.L., Bangs, N.L., Bourlange, S., Broilliard, J., Brückmann, W., Corn, E.R., Davis, E.E., Flemings, P.B., Goldberg, D.B., Gulick, S.S., Hansen, M.B., Hayward, N., Hills, D.J., Hunze, S., Ienaga, M., Ishiguro, H., Kinoshita, M., Macdonald, R.D., McNeill, L., Obana, S., Hong, O.S., Peacock, S., Pettigrew, T.L., Saito, S., Sawa, T., Thaiprasert, N., Tobin, H.J., Tsurumi, H., 2002. Proc. ODP, Initial Rep., 196, College Station, TX, (Ocean Drilling Program)]. The upper boundary of the décollement is marked by several sets of conductive fractures and by high variability in physical properties. The décollement zone is characterized by intense brittle fracturing. These fractures are considered to be the consequence of cyclic stresses and high fluid pressures in this zone. We analyzed fracture dips and their orientations at both sites and found that they are all consistent with a unique stress field model surrounding the two sites.     

Overpressure within upper continental slope sediments from CPTU data,Gulf of Lion,NW Mediterranean Sea

Data from in situ piezocone tests (CPTU) and laboratory analyses are utilized for the interpretation of the stress history of Quaternary sedimentary sequences in the upper continental slope of the Gulf of Lion, northwestern Mediterranean Sea. A CPTU based preconsolidation pressure profile referenced to the current effective stress indicates that the deposit is underconsolidated from 12 meters below the seafloor (mbsf) down to at least 150 mbsf. Excess pore pressure below 12 mbsf is further supported by results from oedometer and dissipation tests. Subseafloor pockmarks and indications of free gas in seismic reflection profiles reveal four main overpressure sources (SI–SIV) with overpressure ratios >0.3 at subseafloor depths coinciding with levels where the dominantly silty-clayey sediment contains increased proportions of sand. We relate the excess pore pressure related to free gas due to gas exsolution processes and sea level variations driven by Pleistocene sea level changes.     

Book reviews

Books review in this article:
Tide-influenced Sedimentary Environments and Facies, ed. by P. L. de Boer, A. van Gelder and S. D. Nio
Tides, Surges and Mean Sea-Level, A Handbook for Engineers and Scientists, by D. T. Pugh
Reservoir Sedimentology, ed. by R. W. Tillman and K. J. Weber
Sedimentation and Tectonics of the Welsh Basin, ed. by W. R. Fitches and N. H. Woodcock
Sediment Transport in Gravel Bed Rivers, ed. by C. R. Thorne, J. C. Bathurst & R. D. Hey
Periglacial Processes and Landforms in Britain and Ireland, ed. by John Broadman
Biolaminated Deposits, by G. Gerdes & W. E. Krumbein
Dinosaurs Past and Present, ed. by S. J. Czerkas and E. C. Olson.
Abrupt Climatic Change, Evidence and Implications, ed. by W. H. Berger and L. D. Labeyrie
The Morphodynamics of the Wadden Sea, by J. Ehlers, A. A. Balkema
Paleokarst, ed. by N. P. James and P. W. Choquette
Sea-level Fluctuation and Coastal Evolution, ed. by D. Nummedal, O. H. Pilkey and J. D. Howard     

Book reviews

Book reviews in this article:
Sedimentary Cover—North American Craton: US
The Geology of North America, Vol. D-2, ed. by L. L. Sloss
Thermal History of Sedimentary Basins: Methods and Case Histories, ed. by N. D. Naeser and T. H. McCulloh
Origin and Migration of Subsurface Sedimentary Brines, SEPM Short Course No. 21, by J. S. Hanor
Evaporites and Hydrocarbons, ed. by B. C. Schreiber.
Phanerozoic Ironstones, ed. by T. P. Young and W. E. G. Taylor.
Green Marine Clays, ed. by G. S. Odin
Siliceous Sedimentary Rock-Hosted Ores and Petroleum, ed. by J. R. Hein.
Neodymium Isotope Geochemistry, by D. J. DePaolo
The Beginning of the Age of Dinosaurs. Faunal Change across the Triassic-Jurassic Boundary, ed. by K. Padian.
Basics of Physical Stratigraphy and Sedimentology, by W. J. Fritz and J. N. Moore.
Techniques in Sedimentology, ed. by Maurice Tucker
The Physics of Sediment Transport by Wind and Water, a Collection of Hallmark Papers by R. A. Bagnold, ed. by C. R. Thorne, R. C. MacArthur and J. B. Bradley
Siliceous Deposits of the Tethys and Pacific Regions, ed. by J. R. Hein and J. Obradovic
Diagenesis I and Diagenesis II, ed. by G. V. Chilingarian and K. H. Wolf.
Continental Shelves, ed. by H. Postma and J. J. Zijlstra.
Modern Planktonic Foraminifera, by Ch. Hermleben, M. Spindler and O. R. Anderson
Sedimente und Sedimentgesteine (4th edn), ed. by H. Füchtbauer     

Book reviews

Book review in this article
Antarctic Cenozoic History from the MSSTS-1 Drill Hole McMurdo Sound, ed. by P. J. Barrett
Experimental Fluvial Geomorphology, by Stanley A. Schumm, M. Paul Mosley and William E. Weaver
Diagenetic Bedding: A Model for Marl-Limestone Alterations, by W. Ricken
Cretaceous and Cenozoic Sedimentary Basins of the West Coast Region, South Island, New Zealand. New Zealand Geological Survey Basin Studies1, by S. Nathan, H. J. Anderson, R. A. Cook, R. H. Herzer, R. H. Hoskins, J. I. Raine and D. Smale
The Marine Environment of the U.S. Atlantic Continental Slope and Rise, ed. by J. D. Milliman & W. R. Wright
Shelf Sands and Sandstones, ed. by R. John Knight and J. Ross McLean.
Foreland Basins, ed. by P. A. Allen and P. Homewood.
Proterozoic Geology: Selected Papers from an International Proterozoic Symposium, ed. L. G. Medaris, Jr., C. W. Byers, D. M. Mickelson & W. C. Shanks
Géologie de la Préhistoire, Méthodes, Techniques, Applications, ed. by J. C. Miskovsky
Aeolian Geomorphology (Proceedings of the 17th Annual Binghamton Geomorphology Symposium, September 1986.), ed. by William G. Nickling
Aeolian Dust and Dust Deposits, by K. Pye
Biological Markers in the Sedimentary Record, ed. by R. B. Johns
Stable Isotope Geochemistry, by J. Hoefs
Reef Diagenesis, ed. by J. H. Schroeder and B. H. Purser     

Book Reviews

Book reviewed in this article:
Essays in Geomorphology. G. H. D ury .
The Movement of Beach Sand—Developments in Sedimentology, 5. J. C. I ngle J r .
Manual de Sédimentologie. A. V atan .
Carbonate Rocks—Developments in Sedimentology, 9A. G. V. C hilingar , H. J. B issell and R. W. F airbridge (Editors).
Cyclic Sedimentation—Developments in Sedimentology, 10. P. M c L. D. D uff , A. H allam and E. K. W alton (Editors).     

Books

Book reviewed in this article
Geology of the Manchester Area (Geologists' Association Guide No. 7) by R. M. C. Eagar and F. M. Broadhurst.
The Emergence of Animals: The Cambrian Break-through by Mark A. S. McMenamin and Dianna L. Schultz McMenamin.
Field Geology of High-Grade Gneiss Terrains by C. W. Passchier, J. S. Myers and A. Kröner.
Fossils in the Field: Information Potential and Analysis by Roland Goldring.
Outline and Guide to the Geology of Guernsey by R. A. Roach and others.     

融冰期北极楚科奇海陆架中心区硅限制与来源补充

相对氮亏损(N:P约为7,小于16)的太平洋入流水携带的营养盐是支撑北冰洋上层生态系统的重要物质基础。海冰消退,光限制消失,楚科奇海陆架存在强烈的营养盐消耗与利用,广泛认为其表现为氮限制,因此该区域重点关注氮元素循环,对于硅元素的相关研究较少。本文基于2016年中国第七次北极科学考察和中国-俄罗斯首次联合北极科学考察两个同步进行的航次调查结果,全面展示了融冰期整个楚科奇海陆架区的营养盐分布格局。结果显示,硝酸盐和亚硝酸盐表层基本耗尽;硅酸盐表现为中心低,周围高,陆架中心区是强烈的硅限制区域,受到硅和氮的共同限制。沿着太平洋入流方向,S01、R01、LV77-01站位30 m以深硅酸盐浓度高于太平洋入流水端员,说明沉积物孔隙水向底层水释放硅酸盐,因此在浅水陆架区孔隙水可作为上层海洋硅酸盐的潜在来源。本研究结合文献数据计算得到楚科奇海陆架沉积物-水界面硅酸盐年通量为630.78 mmol·m^-2·a^-1,总量为3.75×10¹¹ mol·a^-1,是太平洋入流水所携带硅酸盐年通量的一半(6.59×10¹¹ mol·a^-1),表明沉积物孔隙水也是楚科奇海陆架硅酸盐的重要来源。     

TERRA BOOKS

Book reviewed in this article:
THREE OF A KIND Carbonate Sedimentology. M.E. Tucker and V.P. Wright
Carbonate Diagenesis and Porosity. C.H. Moore
Carbonate Platforms; facies, sequences and evolution. M.E. Tucker, J.L Wilson, P.D. Crevello, J.R. Sarg and J.F. Read (eds)
MORPHOMETRIC TOOLS FOR LANDMARK DATA: GEOMETRY AND BIOLOGY. Fred L. Bookstein     

Les auditeurs polonais des cours de minéralogie de René Just Haüy au Muséum national d'Histoire naturelle,Paris

The paper analyses a list of thirty-four Poles, listeners to the mineralogy lectures given by R.-J. Haüy at MNHN in Paris. These students played an important role in the history of Polish Earth Sciences (S. Staszic and F. Drzewiński), but also in other scientific fields (J. Markowski, I. Ab?amowicz, F. Drzewiński, M.A. Paw?owicz, J.K. Skrodzki, E.K. Nowicki), and even in political and cultural life of Poland (A. Downarowicz, J. Weyssenhoff, S. Plater, J. Bieliński, F. Potocki). This paper presents later relations between R.-J. Haüy and his Polish students. A possibility of the Poles' attendance to mineralogy lectures given at other Parisian scientific institutions, like the ‘École des mines’ and the ‘College de France’, is also discussed. To cite this article: R. Tarkowski, P. Daszkiewicz, C. R. Geoscience 338 (2006).     

Nitrogen-15 Isotope Enrichment in Benthic Boundary Layer Gases of a Stratified Eutrophic Iron and Manganese Rich Lake

The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km²), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion, hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values of δ¹⁵N [N₂] ranged from −1 to 0.28‰ in the epilimnion, −1.5 to 1.25‰ in the hypolimnion, −1.8 to 12.2‰ in the benthic boundary layer and −0.7 to 3.5‰ in sediment pore waters. Values of δ¹⁵N [N₂] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification. Increases in ¹⁵N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen concentrations <6.3 μM) and may be related to abundant ammonium substrate (up to 275 μM) to support denitrification. Nitrate concentrations increased up to 36 μM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ¹⁵N [N₂] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of Lake Ngapouri. The changes in δ¹⁵N [N₂] values indicate the potential use of isotope ratios to identify and quantify potential chemo-nitrification/denitrification in the water column and sediment pore waters of lakes.     

Book reviews

Books review in this article:
Recognition of Fluvial Depositional Systems and their Resource Potential—SEPM Short Course No 19, by R. M. Flores, F. G. Ethridge, A. D. Miall, W. E. Galloway & T. D. Fouch
Sedimentology of Gravels and Conglomerates, ed. by Emlyn H. Koster & Ron J. Steel
Quaternary Geology and Environment in China, ed. by Liu Tung-sheng et al., China Ocean Press
Coastal and Estuarine Sediment Dynamics, by Keith R. Dyer
Review of Jurassic sedimentary evolution and nappe emplacement in the Argolis Peninsula (Peloponnesus, Greece), by Peter O. Baumgartner
An Introduction to Carbonate Sediments and Rocks, by Terence P. Scoffin
Roles of Organic Matter in Sediment Diagenesis, ed. by D. L. Gautier
Deep Ocean Sediment Transport, ed. by A. R. M. Nowell and C. D. Hollister     

基于流固耦合的强震大型滑坡水力激发效应研究

2008年汶川Ms8.0级强震触发了体积近12×108 m3的大光包滑坡。该滑坡发生于古生代碳酸盐岩地层,滑带地质背景为斜坡内部深埋400 m、最大厚度达5 m的先期层间构造错动带。最新调查表明,该错动带是斜坡内部地下水通道,错动带岩体处于饱和状态。为揭示强震过程与地下水相关的大光包滑坡启动机制,提出了一种具有软弱层带的硬质碳酸盐岩边坡简化模型,将层间构造错动带概化为碳酸盐岩硬层内部软弱层带,采用FLAC3D程序中的流固耦合算法模拟了模型的响应特性。研究结果表明:强震过程中软弱层带上下碳酸盐岩硬层的变形响应时间、波型、大小出现明显差异,上硬层相对于下硬层产生了张离、压缩和剪切3种非协调变形模式,由此对软弱层带产生了振动冲压-张拉和振动剪切动力学行为,饱水软弱层带形成了具有瞬间放大和累积增涨特征的超孔隙水压力。这里将上下硬层差异性变形称为非协调变形,认为非协调变形是软弱层带应力放大成因,推测软弱层带应力瞬间放大以及放大应力长持时作用下的岩体致损是超孔隙水压力激发和累积的成因;强震过程软弱层带超孔隙水压力导致其内有效应力快速降低,使得斜坡前部锁固段应力快速集中,而后被突然剪断,滑坡骤然启动,揭示了强震过程中超孔隙水压力是大光包滑坡启动的主要原因。