Thérèse Mound: a case study of coral bank development in the Belgica Mound Province,Porcupine Seabight     

Ben De Mol  Max Kozachenko  Andy Wheeler  Hugo Alvares  Jean-Pierre Henriet  Karine Olu-Le Roy 《International Journal of Earth Sciences》2007,96(1):103-120

High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime.  相似文献   

Petrogenesis of base metal sulphide assemblages of some peridotites from the Kaapvaal craton (South Africa)     

Jean-Pierre Lorand  Michel Grégoire 《Contributions to Mineralogy and Petrology》2006,151(5):521-538

Thirty-two peridotite xenoliths from kimberlitic pipes of the Kaapvaal craton were analysed for S and studied in reflected light microscopy and electron microprobe. Correlation between whole-rock S concentrations and sulphide modal abundances has been obscured by kimberlite-related sulphur within the mantle and by low-temperature contamination processes during emplacement. Mantle-derived base metal sulphides (BMS) occur as solitary inclusions (SI) and intergranular blebs. Unfractured SI encloses intergrowths of Ni-poor and Ni-rich monosulphide solid solution (Mss) phases, coexisting with pentlandite (Pn) and Cu-rich sulphides. Textural relationships between Mss phases and Cu-sulphides are consistent with fractional crystallization of Mss from a Cu–Fe–Ni sulphide melt. Pn-rich euhedral SI may have crystallized from a more metal-rich sulphide melt. However, the opaque mineral assemblages of both fractured sulphide inclusions and intergranular BMS point to a progressive desulphurization of Mss, yielding Pn-rich grains, often replaced by Fe-poor heazlewoodite and abundant magnetite, while Cu-sulphides are replaced by native copper. This trend is consistent with reducing conditions generated by low-temperature serpentinization. A residual origin cannot be ruled out for the Mss enclosed in the most refractory peridotites, although their Ni/Fe ratios are too low to be consistent with an equilibration with olivine at magmatic temperatures. Modal abundances of mantle-derived BMS increase in the Fe-enriched metasomatized peridotites. At least two BMS precipitation processes can be recognized: (1) precipitation of Fe–Cu-rich immiscible sulphide melts in phlogopite-(ilmenite–rutile) peridotites and (2) sulphidation reactions from an H₂S-rich fluid phase in phlogopite-K richterite peridotites.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.  相似文献   

David D. Pollard, Raymond C. Fletcher, Fundamentals of structural geology, ISBN 0521839270, Prices: 45.00£ and 80.00 US$; convert to Euros if you live in continental Europe.     

Jean-Pierre Burg 《Tectonophysics》2006,412(3-4):289-290

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δ13C variation of soil organic matter as an indicator of vegetation change during the Holocene in central Cameroon     

Thierry Desjardins  Bruno Turcq  Jean-Pierre Nguetnkam  Gaston Achoundong  Magloire Mandeng-Yogo  Fethyé Cetin  Anne-Marie Lézine 《Comptes Rendus Geoscience》2013,345(7-8):266-271

In order to better understand the dynamics of the forest–savanna mosaic from central Cameroon, we analyzed ¹³C and ¹⁴C profiles of six oxisols: two under forests and four under savannas. The δ¹³C soil profiles collected in the forests indicate that these environments are stable at least since the mid-Holocene, whereas the areas currently covered by savannas were formerly occupied by more forested vegetations. The ¹⁴C dating of organic matter indicate that the late extension of the savannas in central Cameroon date from the Late Holocene, starting from 4000–3500 ¹⁴C yr BP.  相似文献   

Geochronological arguments for a close relationship between surficial formation profiles and environmental crisis (c. 3000–2000 BP) in Gabon (Central Africa)     

Denis Thiéblemont  Christine Flehoc  Michel Ebang-Obiang  Christophe Rigollet  Jean-Pierre Prian  François Prognon 《Comptes Rendus Geoscience》2013,345(7-8):272-283

We present new ¹⁴C data on charcoal fragments recovered from the lower (coarse-grained Stone Line) and upper (fine-grained Cover Horizon) portions of surficial formation profiles in Gabon. These data and others compiled from the literature enable a reconstruction of the Upper Holocene geological regional history of Gabon. The connection between the geological events recorded in the surficial formations and the Upper Holocene environmental crisis is discussed and a scenario connecting geological events with climatic and environmental changes is proposed. Such a scenario suggests that following the climatic crisis, the reconstitution of soils by aeolian sedimentation could have been an important factor of Bantu expansion.  相似文献   

Imaging the heart of astrophysical objects with optical long-baseline interferometry     

J.-P. Berger  F. Malbet  F. Baron  A. Chiavassa  G. Duvert  M. Elitzur  B. Freytag  F. Gueth  S. H?nig  J. Hron  H. Jang-Condell  J.-B. Le Bouquin  J.-L. Monin  J. D. Monnier  G. Perrin  B. Plez  T. Ratzka  S. Renard  S. Stefl  E. Thiébaut  K. R. W. Tristram  T. Verhoelst  S. Wolf  J. Young 《Astronomy and Astrophysics Review》2012,20(1):1-55

The number of publications of aperture-synthesis images based on optical long-baseline interferometry measurements has recently increased due to easier access to visible and infrared interferometers. The interferometry technique has now reached a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. In writing this paper our motivation was twofold: (1) review and publicize emblematic excerpts of the impressive corpus accumulated in the field of optical interferometry image reconstruction; (2) discuss future prospects for this technique by selecting four representative astrophysical science cases in order to review the potential benefits of using optical long-baseline interferometers. For this second goal we have simulated interferometric data from those selected astrophysical environments and used state-of-the-art codes to provide the reconstructed images that are reachable with current or soon-to-be facilities. The image-reconstruction process was ??blind?? in the sense that reconstructors had no knowledge of the input brightness distributions. We discuss the impact of optical interferometry in those four astrophysical fields. We show that image-reconstruction software successfully provides accurate morphological information on a variety of astrophysical topics and review the current strengths and weaknesses of such reconstructions. We investigate how to improve image reconstruction and the quality of the image possibly by upgrading the current facilities. We finally argue that optical interferometers and their corresponding instrumentation, existing or to come, with six to ten telescopes, should be well suited to provide images of complex sceneries.  相似文献   

From Jurassic rifting to Cretaceous subduction in NW Iranian Azerbaijan: geochronological and geochemical signals from granitoids     

Anna?LechmannEmail authorView author&#;s OrcID profile  Jean-Pierre?Burg  Peter?Ulmer  Ali?Mohammadi  Marcel?Guillong  Mohammad?Faridi 《Contributions to Mineralogy and Petrology》2018,173(12):102

Previous interpretations of a Jurassic subduction in Iran were based on trace element classification diagrams for granitoids, but their reliability is questionable, underscored by modern examples of continental break-up zones such as the Baja California. We present new field observations, bulk rock geochemistry, Sr and Nd isotope analyses and U–Pb zircon geochronology to assess the age and tectonic setting of previously undated intermediate to felsic magmatic rocks cropping out in the Precambrian basement of NW Iranian Azerbaijan. The geochronology revealed an uneven distribution in space and time: Late Jurassic (159–154 Ma) intrusions and dikes are alkaline to calc-alkaline. Their melt source is mantle dominated with a distinct continental contribution disclosed by radiogenic isotopes and abundant inherited zircon cores. Mid-Cretaceous (112–96 Ma) plutonic bodies and associated volcanic rocks occur only to the east of the major Siah Cheshmeh–Khoy Fault. They have geochemical signatures typical of a metasomatized mantle. In consistence with the sedimentation history of the area, our new interpretation attributes the Late Jurassic magmatism to thinning of a continental lithosphere in a rift-related setting. Mid-Cretaceous magmatism was produced by oceanic subduction beneath the Central Iran continent. We interpret the 40-Ma age gap between the two magmatic episodes as the time of opening of the oceanic basin witnessed by the Khoy ophiolite in the study area.  相似文献   

Acoustic monitoring of gas emissions from the seafloor. Part I: quantifying the volumetric flow of bubbles     

Isabelle Leblond  Carla Scalabrin  Laurent Berger 《Marine Geophysical Researches》2014,35(3):191-210

Three decades of continuous ocean exploration have led us to identify subsurface fluid related processes as a key phenomenon in marine earth science research. The number of seep areas located on the seafloor has been constantly increasing with the use of multi-scale imagery techniques. Due to recent advances in transducer technology and computer processing, multibeam echosounders are now commonly used to detect submarine gas seeps escaping from the seafloor into the water column. A growing number of en-route surveys shows that sites of gas emissions escaping from the seafloor are much more numerous than previously thought. Estimating the temporal variability of the gas flow rate and volumes escaping from the seafloor has thus become a challenge of relevant interest which could be addressed by sea-floor continuous acoustic monitoring. Here, we investigate the feasibility of estimating the volumetric flow rates of gas emissions from horizontal backscattered acoustic signals. Different models based on the acoustic backscattering theory of bubbles are presented. The forward volume backscattering strength and the inversion volumetric flow rate solutions were validated with acoustic measurements from artificial gas flow rates generated in controlled sea-water tank experiments. A sensitivity analysis was carried out to investigate the behavior of the 120-kHz forward solution with respect to model input parameters (horizontal distance between transducer and bubble stream, bubble size distribution and ascent rate). The most sensitive parameter was found to be the distance of the bubble stream which can affect the volume backscattering strength by 20 dB within the horizontal range of 0–200 m. Results were used to derive the detection probability of a bubble stream for a given volume backscattering strength threshold according to different bubble flow rates and horizontal distance.  相似文献   

Acoustic monitoring of gas emissions from the seafloor. Part II: a case study from the Sea of Marmara     

Gaye Bayrakci  Carla Scalabrin  Stéphanie Dupré  Isabelle Leblond  Jean-Baptiste Tary  Nadine Lanteri  Jean-Marie Augustin  Laurent Berger  Estelle Cros  André Ogor  Christos Tsabaris  Marc Lescanne  Louis Géli 《Marine Geophysical Researches》2014,35(3):211-229

A rotating, acoustic gas bubble detector, BOB (Bubble OBservatory) module was deployed during two surveys, conducted in 2009 and 2011 respectively, to study the temporal variations of gas emissions from the Marmara seafloor, along the North Anatolian Fault zone. The echosounder mounted on the instrument insonifies an angular sector of 7° during a given duration (of about 1 h). Then it rotates to the next, near-by angular sector and so forth. When the full angular domain is insonified, the “pan and tilt system” rotates back to its initial position, in order to start a new cycle (of about 1 day). The acoustic data reveal that gas emission is not a steady process, with observed temporal variations ranging between a few minutes and 24 h (from one cycle to the other). Echo-integration and inversion performed on the acoustic data as described in the companion paper of Leblond et al. (Mar Geophys Res, 2014), also indicate important variations in, respectively, the target strength and the volumetric flow rates of individual sources. However, the observed temporal variations may not be related to the properties of the gas source only, but reflect possible variations in sea-bottom currents, which could deviate the bubble train towards the neighboring sector. During the 2011 survey, a 4-component ocean bottom seismometer (OBS) was co-located at the seafloor, 59 m away from the BOB module. The acoustic data from our rotating, monitoring system support, but do not provide undisputable evidence to confirm, the hypothesis formulated by Tary et al. (2012), that the short-duration, non-seismic micro-events recorded by the OBS are likely produced by gas-related processes within the near seabed sediments. Hence, the use of a multibeam echosounder, or of several split beam echosounders should be preferred to rotating systems, for future experiments.  相似文献   

Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea     

Nicolas Kolodziejczyk  Frédéric Marin  Bernard Bourlès  Yves Gouriou  Henrick Berger 《Climate Dynamics》2014,43(11):3025-3046

The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 isopycnal layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.  相似文献