Seismic‐stratigraphic record of a deglaciation sequence: from the marine Laflamme Gulf to Lake Saint‐Jean (late Quaternary,Québec,Canada)     

Alexis Nutz  Jean‐François Ghienne  Mathieu Schuster  Raphaël Certain  Nicolas Robin  Claude Roquin  Olivier Raynal  Frédéric Bouchette  Philippe Duringer  Pierre A. Cousineau 《Boreas: An International Journal of Quaternary Research》2014,43(2):309-329

The stratigraphy of the last deglaciation sequence is investigated in Lake Saint‐Jean (Québec Province, Canada) based on 300 km of echo‐sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice‐front recession to the present‐day situation. Ten seismic units have been identified that reflect spatio‐temporal variations in depositional processes characterizing different periods of the Saint‐Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio‐isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river‐related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind‐driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf‐type body. The fingerprints of a forced regression are well expressed by mouth‐bar systems and by the shoreface–shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth‐bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf‐type body, respectively. The Lake Saint‐Jean record is an example of a regressive succession driven by a glacio‐isostatic rebound and showing the transition from late‐glacial to post‐glacial depositional systems.  相似文献   

Cycles of humid‐dry climate conditions around the P/E boundary: new stable isotope data from terrestrial organic matter in Vasterival section (NW France)     

Jean‐Yves Storme  Christian Dupuis  Johann Schnyder  Florence Quesnel  Sylvain Garel  Alina I. Iakovleva  Paola Iacumin  Antonietta Di Matteo  Mathieu Sebilo  Johan Yans 《地学学报》2012,24(2):114-122

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Atmospheric control of the cooling rate of impact melts and cryolavas on Titan’s surface     

Ashley Gerard Davies  Christophe Sotin  Dennis L. Matson  Julie Castillo-Rogez  Torrence V. Johnson  Mathieu Choukroun  Kevin H. Baines 《Icarus》2010,208(2):887-895

As on Earth, Titan’s atmosphere plays a major role in the cooling of heated surfaces. We have assessed the mechanisms by which Titan’s atmosphere, dominantly N₂ at a surface pressure of 1.5 × 10⁵ Pa, cools a warm or heated surface. These heated areas can be caused by impacts generating melt sheets and (possibly) by endogenic processes emplacing cryolavas (a low-temperature liquid that freezes on the surface). We find that for a cooling cryolava flow, lava lake, or impact melt body, heat loss is mainly driven by atmospheric convection. Radiative heat loss, a dominant heat loss mechanism with terrestrial silicate lava flows, plays only a minor role on Titan. Long-term cooling and solidification are dependent on melt sheet or flow thickness, and also local climate, because persistent winds will speed cooling. Relatively rapid cooling caused by winds reduces the detectability of these thermal events by instruments measuring surface thermal emission. Because surface temperature drops by ≈50% within ≈1 day of emplacement, fresh flows or impact melt may be difficult to detect via thermal emission unless an active eruption is directly observed. Cooling of flow or impact melt surfaces are orders of magnitude faster on Titan than on airless moons (e.g., Enceladus or Europa).Although upper surfaces cool fast, the internal cooling and solidification process is relatively slow. Cryolava flow lengths are, therefore, more likely to be volume (effusion) limited, rather than cooling-limited. More detailed modeling awaits constraints on the thermophysical properties of the likely cryomagmas and surface materials.  相似文献   

The Corossol structure: A possible impact crater on the seafloor of the northwestern Gulf of St. Lawrence,Eastern Canada     

Patrick Lajeunesse  Guillaume St‐Onge  Jacques Locat  Mathieu J. Duchesne  Michael D. Higgins  Richard Sanfaçon  Joseph Ortiz 《Meteoritics & planetary science》2013,48(12):2542-2558

We report on a 4.1 (±0.2) km diameter and 185 m deep circular submarine structure exposed on the seabed in >40 m water depths in the northwestern Gulf of St. Lawrence (Eastern Canada) from the analysis of high‐resolution multibeam bathymetric and seismic data. The presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures. Also, other origins, such as kimberlites, intrusions, karsts, or diapirs, can be eliminated on geological criteria. A single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition, assumed to be impact melts, and a single quartz grain with planar intersection features thought to be shock‐induced planar deformation features (PDFs). The absolute age of this possible impact structure is unknown, but its geological setting indicates that it was formed long after the Mid‐Ordovician and before regional pre‐Quaternary sea‐level lowstands. Present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure.  相似文献   

Nonuniform cratering of the Moon and a revised crater chronology of the inner Solar System   总被引：1，自引：0，他引：1  

Mathieu Le Feuvre  Mark A. Wieczorek 《Icarus》2011,214(1):1-7225

We model the cratering of the Moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner Solar System, in order to refine the crater chronology method. Impact occurrences, locations, velocities and incidence angles are calculated semi-analytically, and scaling laws are used to convert impactor sizes into crater sizes. Our approach is generalizable to other moons or planets. The lunar cratering rate varies with both latitude and longitude: with respect to the global average, it is about 25% lower at (±65°N, 90°E) and larger by the same amount at the apex of motion (0°N, 90°W) for the present Earth-Moon separation. The measured size-frequency distributions of lunar craters are reconciled with the observed population of near-Earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith. Varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size-frequency distributions. We give a revised analytical relationship between the number of craters and the age of a lunar surface. For the inner planets, expected size-frequency crater distributions are calculated that account for differences in impact conditions, and the age of a few key geologic units is given. We estimate the Orientale and Caloris basins to be 3.73 Ga old, and the surface of Venus to be 240 Ma old. The terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 Ma. Better knowledge of the orbital dynamics, crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps, from the observation of asteroids to the formation of craters. Our model may be inaccurate for periods prior to 3.5 Ga because of a different impactor population, or for craters smaller than a few kilometers on Mars and Mercury, due to the presence of subsurface ice and to the abundance of large secondaries, respectively. Standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3.5 Ga ago, and give self-consistent estimates of the planetary cratering rates relative to the Moon.  相似文献   

The effect of silica and natural organic matter on the Fe(II)-catalysed transformation and reactivity of Fe(III) minerals   总被引：3，自引：0，他引：3  

Adele M. Jones  Jerome Rose 《Geochimica et cosmochimica acta》2009,73(15):4409-4422

The Fe(II)-catalysed transformation of synthetic schwertmannite, ferrihydrite, jarosite and lepidocrocite to more stable, crystalline Fe(III) oxyhydroxides is prevented by high, natural concentrations of Si and natural organic matter (NOM). Adsorption isotherms demonstrate that Si adsorbs to the iron minerals investigated and that increasing amounts of adsorbed Si results in a decrease in isotope exchange between aqueous Fe(II) and the Fe(III) mineral. This suggests that the adsorption of Si inhibits the direct adsorption of Fe(II) onto the mineral surface, providing an explanation for the inhibitory effect of Si on the Fe(II)-catalysed transformation of Fe(III) minerals. During the synthesis of lepidocrocite and ferrihydrite, the presence of equimolar concentrations of Si and Fe resulted in the formation of 2-line ferrihydrite containing co-precipitated Si in both cases. Isotope exchange experiments conducted with this freeze-dried Si co-precipitated ferrihydrite species (Si-ferrihydrite) demonstrated that the rate and extent of isotope exchange between aqueous Fe(II) and solid ⁵⁵Fe(III) was very similar to that of 2-line ferrihydrite formed in the absence of Si and which had not been allowed to dry. In contrast to un-dried ferrihydrite formed in the absence of Si, Si-ferrihydrite did not transform into a more crystalline Fe(III) mineral phase over the 7-day period of investigation. Reductive dissolution studies using ascorbic acid demonstrated that both dried Si-ferrihydrite and un-dried 2-line ferrihydrite were very reactive, suggesting these species may be major contributors to the rapid release of dissolved iron following flooding and the onset of conditions conducive to reductive dissolution in acid sulphate soil environments.  相似文献   

Caractérisation par résonance paramagnétique électronique (RPE) de quartz naturels issus de différentes sources     

Mathieu Duttine  Gérard Villeneuve  Françoise Bechtel  Gérard Demazeau 《Comptes Rendus Geoscience》2002,334(13):949-955

Natural quartz crystals coming from Madagascar, Angola, Brazil, and Spain were studied by EPR after β irradiation in order to characterise the paramagnetic centres due to impurities, and examine in which way their relative proportion could constitute a useful criterion for origin researches. In all our samples, EPR experiments revealed germanium centres [GeO₄/M⁺]° with M = Li or Na, aluminium ones [AlO₄/h]° and two titanium centres ([TiO₄/H⁺]° and [TiO₄/M⁺]°) also appeared, except for samples coming from Spain. The comparison of the relative concentrations of paramagnetic species led us on to draw diagrams that allowed distinguishing the origins of the studied samples using only EPR spectra. To cite this article: M. Duttine et al., C. R. Geoscience 334 (2002) 949–955.  相似文献   

Evidence for Non-Conservative Behaviour of Chlorine in Humid Tropical Environments     

Jerome Viers  Bernard Dupre  Jean-Jacques Braun  Remi Freydier  Sacha Greenberg  Jules Ndam Ngoupayou  Lus Sigha Nkamdjou 《Aquatic Geochemistry》2001,7(2):127-154

The knowledge of the biogeochemical cycle of chlorine (Cl)is important since this element is used as a tracer of geochemical and hydrological processes in oceanic or continental environments. More specifically, Cl can be used to correct surface water composition from atmospheric contribution in order to calculate precise chemical weathering rates in watersheds. Beyond the problem of potential Cl sources in a given watershed, which is directly related to the lithology, vegetation, and industrial activities, the Cl normalization is based on the assumption that this element behaves conservatively during surface processes (e.g., chemical weathering, adsorption/desorption processes).The purpose of the present study is to forecast the geochemical behavior of Cl in a forested ecosystem located under humid tropical environment.For this reason, we have analyzed the Cl (and also Ca and Na) concentrations ofsurface waters (rainwater, groundwater, river water) over a two-year period in the Nsimi–Zoetele watershed (Cameroon).The Cl mass balance for the watershed appears to be equilibrated over the studied period (1995–1996) but Cl behavior in Mengong River draining the watershed suggests a non-conservative behavior. Indeed, Cl concentrationsin the Mengong River are low during dry seasons and high during wet seasons, which is the reverse tendency to what is usually observed taking into account dilution and evaporation processes. As Cl concentrations in the Mengong River are lower than those measured in all the feeding reservoirs, Cl should be adsorbed onto the soils of the watershed. However, as the Cl mass balance is equilibrated over the whole-year, Cl should be adsorbed and releasedat a seasonal scale. The results we obtained for this small watershed were not generalized for a larger studied basin (i.e., Nyong River basin). Even if these results should be followed by further investigations, this study suggests that Cl normalization should be used with caution to avoid under- or over-estimation of chemical weathering rates.  相似文献   

Discussion of “Acoustic profiling of fine suspension concentration in the changjiang estuary” by Z. Shi, L. F. Ren, and L. J. Hamilton. 1999.Estuaries 22:648–656     

Jerome P. -Y. Maa  K. -J. Sun 《Estuaries and Coasts》2001,24(1):135-137

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Urban and suburban storm water runoff as a source of polycyclic aromatic hydrocarbons (PAHs) to Massachusetts estuarine and coastal environments   总被引：1，自引：0，他引：1  

Charles A. Menzie  Susanne S. Hoeppner  Jerome J. Cura  Jonathan S. Freshman  Elizabeth N. LaFrey 《Estuaries and Coasts》2002,25(2):165-176

Urban and suburban storm water runoff from ten locations in eastern Massachusetts was analyzed for 39 polycyclic aromatic hydrocarbons (PAHs) compounds. Similar profiles in PAH composition were observed for groups of samples and appear to reflect land use. The largest group includes, urban storm water from areas with a mix of industrial, commercial, and residential use. Fluoranthene, phenanthrene, pyrene, chrysene, and benzo (b) fluoranthene were the predominant compounds in this group, but lighter molecular weight PAHs were also present. Sources of PAHs to storm water include a combination of petroleum and combustion. The profile of PAH compounds in local atmospheric deposition was similar to urban storm water, but differed in several of the predominant compounds. PAHs in storm water could increase the levels of these compounds in nearshore sediments and may be the most important source of high molecular weight PAHs to these environments.  相似文献