A new Cenomanian ichthyofauna from southeastern Morocco and its relationships with other early Late Cretaceous Moroccan faunas     

Cavin  Lionel  Dutheil  Didier B. 《Geologie en Mijnbouw》1999,78(3-4):261-266

A new ichthyofauna from southeastern Morocco, comprising five forms, is briefly discussed. The faunal composition differs from the Early Cenomanian Kem Kem and Early Turonian Goulmima assemblages, but is close to that from Jebel Tselfat. We propose a Late Cenomanian age for the new fauna and that from Jebel Tselfat. The evolution of these fish assemblages shows the Moroccan fish faunas to have been related to those from South America until at least the Early Turonian. Central Tethyan influence on faunas seems to have been restricted to a short period of time during the beginning of the Late Cenomanian transgressive phase.  相似文献   

The role of regolith redistribution in influencing the evolution of the shapes of asteroids     

Lionel Wilson  Klaus Keil 《Meteoritics & planetary science》2001,36(6):817-829

Abstract— ‐Major surface fissures and relatively large‐scale, angular surface irregularities are expected to have been present on many asteroids at early stages in their histories as a byproduct of at least two processes (impact disruption and reassembly into rubble piles for all classes of asteroid and, for carbonaceous chondrite parent bodies, aqueous alteration) which led to the low bulk densities currently being observed for asteroids. However, in all cases where high‐enough resolution images exist, such abrupt, deep irregularities are not observed. We model the spatial redistribution of impact‐generated regolith on an asteroid with an idealized irregular shape to show how the complex gravitational field of such a body will lead to the systematic infilling of deep valleys in the surface. Our analysis emphasizes the high efficiency with which regolith redistribution can act to disguise the internal structures of asteroids with sizes in the 20–100 km range.  相似文献   

Spatio-temporal evolution of the Choisille River (southern Parisian Basin,France) during the Weichselian and the Holocene as a record of climate trend and human activity in north-western Europe     

Eymeric Morin  Jean-Jacques Macaire  Florent Hinschberger  Isabelle Gay-Ovéjéro  Stéphane Rodrigues  Jean-Paul Bakyono  Lionel Visset 《Quaternary Science Reviews》2011,30(3-4):347-363

The morpho-sedimentary evolution of the Choisille floodplain (lowland river, catchment: 288 km²), a tributary of the River Loire in the south-western Parisian Basin, was studied through 61 core drillings along eight transects and a geophysical survey located in four stretches of the river: stretches A and B correspond to two sub-catchments, and stretches C and D are in the main valley. Sixty ¹⁴C and four OSL datings were obtained, and sediments were analysed on seven reference cores. Eight phases of evolution differing markedly from the evolution of more northern areas in the Parisian Basin and north-western Europe were identified from spatio-temporal distribution of nine lithological facies. The deepest incision phase (1) occurred during the first part of the Weichselian, followed by the deposition of a gravelly-sandy unit (phase 2) during the Middle Pleniglacial, which was deeply incised (phase 3), probably during the Bölling. From the Allerød up to the last third of the Boreal (phase 4), sedimentation was continuously dominated by peaty deposits, with no evidence of either increased hydraulic energy during the Younger Dryas, or of incision during the LateGlacial–Holocene transition. This trend seems to reflect the specificity of the south-western Parisian Basin climate from the Late Weichselian up to the end of the Boreal, due to the influence of the Atlantic Ocean, compared to more northern areas where the climate was more continental. The downstream incision trend during the last third of the Boreal up to the Subatlantic (phases 5 and 6) indicates a sharp increase in precipitation and vegetation cover; the lack of peaty sediments, widespread in north-western Europe, and also of precipitated carbonates frequent in the Parisian Basin, seems to be due to local physiographic characteristics. The main part of the sediment filling, which is principally silty and retrograde, began during the Subatlantic (phase 7 and 8) as a result of deforestation of the plateaux for crop farming. High human-induced sediment yield and storage concealed the possible impacts of climate change on fluvial dynamics: lithological facies change from phase 7 to 8 can only indicate the autogenic morphological evolution of the floodplain in accretion. The non-univocal upstream–downstream variation in the start of phase 7 shows that sediment yield varied in space and time in the catchment, particularly in relation to the agricultural potential of the different areas; this observation could be used to testify human-induced sedimentation in other catchments.  相似文献   

Surface exposure dating (36Cl and 10Be) of post‐Last Glacial Maximum valley moraines,Lake District,northwest England: some issues and implications     

PETER WILSON  CHRISTOPH SCHNABEL  KLAUS M. WILCKEN  PETER J. VINCENT 《第四纪科学杂志》2013,28(4):379-390

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The geothermal gradient of Io: Consequences for lithosphere structure and volcanic eruptive activity   总被引：1，自引：0，他引：1  

Giovanni Leone  Lionel Wilson 《Icarus》2011,211(1):623-635

We solve numerically the equations describing the transfer of heat through the lithosphere of Io by a mixture of conduction and volcanic advection as proposed by O’Reilly and Davies (O’Reilly, T.C., Davies, G.F. [1981]. Geophys. Res. Lett. 8, 313-316), removing the requirement that average material properties must be used. As expected, the dominance of advective heat transfer by volcanic eruptions means that Io’s geothermal gradient well away from volcanic centres is very small, of order 1 K km⁻¹. This result is independent of any reasonable assumptions about the radiogenic heating rate in the lithosphere. The lithosphere temperature does not increase greatly above the surface temperature until the base of the lithosphere is approached, except in limited areas around shallow magma bodies. As a consequence, solid volatile sulphur compounds mobilized by volcanic processes and re-deposited on the surface of Io commonly remain solid until they reach great depths as they are progressively buried by ongoing activity. For current estimates of the volcanic heat transfer rate, melting of SO₂ does not begin until a depth of ∼20 km and sulphur remains solid to a depth of ∼26 km in a 30 km thick lithosphere. Rising magmas can incorporate fluids from these deep sulphur compound aquifers, and we quantify the major influence that this can have on the bulk density of the magma and hence the resulting possible intrusion and eruption styles.  相似文献   

The global distribution of pyroclastic deposits on Mercury: The view from MESSENGER flybys 1–3     

Laura Kerber  James W. Head  David T. Blewett  Sean C. Solomon  Lionel Wilson  Scott L. Murchie  Mark S. Robinson  Brett W. Denevi  Deborah L. Domingue 《Planetary and Space Science》2011,59(15):1895-1909

We present a global survey of candidate pyroclastic deposits on Mercury, derived from images obtained during MESSENGER flybys 1–3 that provided near-global coverage at resolutions between 5 and 0.5 km/pixel. Thirty-five deposits were identified and characterized and are located principally on the floors of craters, along rims of craters, and along the edge of the Caloris basin. Deposits are commonly centered on rimless, often irregularly shaped pits, mostly between 5 and 45 km in diameter. The deposits identified are generally similar in morphology and absolute reflectance to lunar pyroclastic deposits. Spectrally the deposits appear brighter and redder than background Mercury terrain. On the basis of the available coverage, the candidate pyroclastic deposits appear to be essentially globally distributed. The diameters of the deposits, when mapped to lunar gravity conditions, are larger than their lunar counterparts, implying that more abundant volatiles were present during the typical eruptive process than on the Moon. These observations indicate that if these deposits resulted from hawaiian-style eruptions, the volatile contents required would be between ～1600 and 16,000 ppm CO or an equivalent value of H₂O, CO₂, SO₂, or H₂S (for a more oxidizing interior), or N₂, S₂, CS₂, S₂Cl, Cl, Cl₂, or COS (for a more reducing interior). These abundances are much greater than those predicted by existing models for Mercury's formation. An apparent lack of small deposits, compared with the Moon, may be due to resolution effects, a topic that can be further assessed during the orbital phase of the MESSENGER mission. These results provide a framework within which orbital observations by MESSENGER and the future BepiColombo mission can be analyzed.  相似文献   

Plio-Quaternary stress states in NE Iran: Kopeh Dagh and Allah Dagh-Binalud mountain ranges     

Esmaeil Shabanian  Olivier Bellier  Mohammad R. Abbassi  Lionel Siame  Yassaman Farbod 《Tectonophysics》2010,480(1-4):280-304

NE Iran, including the Kopeh Dagh and Allah Dagh-Binalud deformation domains, comprises the northeastern boundary of the Arabia–Eurasia collision zone. This study focuses on the evolution of the Plio-Quaternary tectonic regimes of northeast Iran. We present evidence for drastic temporal changes in the stress state by inversion of both geologically and seismically determined fault slip vectors. The inversions of fault kinematics data reveal distinct temporal changes in states of stress during the Plio-Quaternary (since ～ 5 Ma). The paleostress state is characterized by a regional transpressional tectonic regime with a mean N140 ± 10°E trending horizontal maximum stress axis (σ₁). The youngest (modern) state of stress shows two distinct strike-slip and compressional tectonic regimes with a regional mean of N030 ± 15°E trending horizontal σ₁. The change from the paleostress to modern stress states has occurred through an intermediate stress field characterized by a mean regional N trending σ₁. The inversion analysis of earthquake focal mechanisms reveals a homogeneous, transpressional tectonic regime with a regional N023 ± 5°E trending σ₁. The modern stress state, deduced from the youngest fault kinematics data, is in close agreement with the present-day stress state given by the inversions of earthquake focal mechanisms. According to our data and the deduced results, in northeast Iran, the Arabia–Eurasia convergence is taken up by strike-slip faulting along NE trending left-lateral and NNW trending right-lateral faults, as well as reverse to oblique-slip reverse faulting along NW trending faults. Such a structural assemblage is involved in a mechanically compatible and homogeneous modern stress field. This implies that no strain and/or stress partitioning or systematic block rotations have occurred in the Kopeh Dagh and Allah Dagh-Binalud deformation domains. The Plio-Quaternary stress changes documented in this paper call into question the extrapolation of the present-day seismic and GPS-derived deformation rates over geological time intervals encompassing tens of millions of years.  相似文献   

Sampling the Cape Verde Mantle Plume: Evolution of Melt Compositions on Santo Antao, Cape Verde Islands   总被引：1，自引：0，他引：1  

HOLM  P. M.; WILSON  J. R.; CHRISTENSEN  B. P.; HANSEN  L.; HANSEN  S. L.; HEIN  K. M.; MORTENSEN  A. K.; PEDERSEN  R.; PLESNER  S.; RUNGE  M. K. 《Journal of Petrology》2006,47(1):145-189

The volcanic history of Santo Antão, NW Cape Verde Islands,includes the eruption of basanite–phonolite series magmasbetween 7·5 and 0·3 Ma and (melilite) nephelinite–phonoliteseries magmas from 0·7 to 0·1 Ma. The most primitivevolcanic rocks are olivine ± clinopyroxene-phyric, whereasthe more evolved rocks have phenocrysts of clinopyroxene ±Fe–Tioxide ± kaersutite ± haüyne ± titanite± sanidine; plagioclase occurs in some intermediate rocks.The analysed samples span a range of 19–0·03% MgO;the most primitive have 37–46% SiO₂, 2·5–7%TiO₂ and are enriched 50–200 x primitive mantle in highlyincompatible elements; the basanitic series is less enrichedthan the nephelinitic series. Geochemical trends in each seriescan be modelled by fractional crystallization of phenocrystassemblages from basanitic and nephelinitic parental magmas.There is little evidence for mineral–melt disequilibrium,and thus magma mixing is not of major importance in controllingbulk-rock compositions. Mantle melting processes are modelledusing fractionation-corrected magma compositions; the modelssuggest 1–4% partial melting of a heterogeneous mantleperidotite source at depths of 90–125 km. Incompatibleelement enrichment among the most primitive magma types is typicalof HIMU OIB. The Sr, Nd and Pb isotopic compositions of theSanto Antão volcanic sequence and geochemical characterchange systematically with time. The older volcanic rocks (7·5–2Ma) vary between two main mantle source components, one of whichis a young HIMU type with ²⁰⁶Pb/²⁰⁴Pb = 19·88, 7/4 =–5, 8/4 0, ⁸⁷Sr/⁸⁶Sr = 0·7033 and ¹⁴³Nd/¹⁴⁴Nd= 0·51288, whereas the other has somewhat less radiogenicSr and Pb and more radiogenic Nd. The intermediate age volcanicrocks (2–0·3 Ma) show a change of sources to two-componentmixing between a carbonatite-related young HIMU-type source(²⁰⁶Pb/²⁰⁴Pb = 19·93, 7/4 = –5, 8/4 = –38,⁸⁷Sr/⁸⁶Sr = 0·70304) and a DM-like source. A more incompatibleelement-enriched component with 7/4 > 0 (old HIMU type) isprominent in the young volcanic rocks (0·3–0·1Ma). The EM1 component that is important in the southern CapeVerde Islands appears to have played no role in the petrogenesisof the Santo Antão magmas. The primary magmas are arguedto be derived by partial melting in the Cape Verde mantle plume;temporal changes in composition are suggested to reflect layeringin the plume conduit. KEY WORDS: radiogenic isotopes; geochemistry; mantle melting; Cape Verde  相似文献   

High slip rate for a low seismicity along the Palu-Koro active fault in central Sulawesi (Indonesia)     

Olivier Bellier  Michel Sébrier  Thierry Beaudouin  Michel Villeneuve  Régis Braucher  Didier Bourlès  Lionel Siame  Eka Putranto  & Indyo Pratomo 《地学学报》2001,13(6):463-470

In eastern Indonesia, the Central Sulawesi fault system consists of complex left-lateral strike-slip fault zones located within the triple junction area between the Pacific, Indo-Australian and Eurasian plates. Seismicity in Central Sulawesi documents low-magnitude shallow earthquakes related, from NW to SE, to the NNW-trending Palu-Koro (PKF) and WNW-trending Matano fault zones. Study of the active fault traces indicates a northward growing complexity in the PKF segmentation. Left-lateral displacement of 370 ± 10 m of streams incised within fans, whose deposition has been dated at 11 000 ± 2300 years, yields a calculated PKF horizontal slip rate of 35 ± 8 mm yr⁻¹. This geologically determined long-term slip rate agrees with the far-field strike-slip rate of 32–45 mm yr⁻¹ previously proposed from GPS measurements and confirms that the PKF is a fast slipping fault with a relatively low level of seismicity.  相似文献   

Arctic versus temperate comparison of risk assessment metrics for 2-methyl-naphthalene     

Olsen GH  Smit MG  Carroll J  Jæger I  Smith T  Camus L 《Marine environmental research》2011,72(4):179-187

Reliable risk assessment approaches for Arctic environments are requested to manage potential impacts associated with increased activities in Arctic regions. We performed toxicity tests on Arctic and temperate species exposed to the narcotic acting oil component, 2-methyl naphthalene. The experimental results were used to quantify concentration causing lethality to 50% of exposed individuals and no-effect concentration (individual level). For estimates at community level, the hazardous concentrations affecting 5% and 50% of the species were calculated from sensitivity distribution curves. These survival metrics were then used to elucidate whether temperate toxicity data used in risk assessment are sufficiently representative for the Arctic. Taking data uncertainty into consideration, we found no regional difference in tolerances to 2-methyl naphthalene either at the species level or at the community level. Hence these data support a conclusion that values of survival metrics for temperate regions are transferrable to the Arctic for the chemical 2-methyl naphthalene, as long as extrapolation techniques are properly applied and uncertainties are taken into consideration.  相似文献