Asteroid taxonomic signatures from photometric phase curves     

Dagmara Anna Oszkiewicz  Edward Bowell  L.H. Wasserman  Karri Muinonen  Antti Penttilä  Tuomo Pieniluoma  David E. Trilling  Cristina A. Thomas 《Icarus》2012,219(1):283-296

We explore the correlation between an asteroid’s taxonomy and photometric phase curve using the H, G₁₂ photometric phase function, with the shape of the phase function described by the single parameter G₁₂. We explore the usability of G₁₂ in taxonomic classification for individual objects, asteroid families, and dynamical groups. We conclude that the mean values of G₁₂ for the considered taxonomic complexes are statistically different, and also discuss the overall shape of the G₁₂ distribution for each taxonomic complex. Based on the values of G₁₂ for about half a million asteroids, we compute the probabilities of C, S, and X complex membership for each asteroid. For an individual asteroid, these probabilities are rather evenly distributed over all of the complexes, thus preventing meaningful classification. We then present and discuss the G₁₂ distributions for asteroid families, and predict the taxonomic complex preponderance for asteroid families given the distribution of G₁₂ in each family. For certain asteroid families, the probabilistic prediction of taxonomic complex preponderance can clearly be made. In particular, the C complex preponderant families are the easiest to detect, the Dora and Themis families being prime examples of such families. We continue by presenting the G₁₂-based distribution of taxonomic complexes throughout the main asteroid belt in the proper element phase space. The Nysa–Polana family shows two distinct regions in the proper element space with different G₁₂ values dominating in each region. We conclude that the G₁₂-based probabilistic distribution of taxonomic complexes through the main belt agrees with the general view of C complex asteroid proportion increasing towards the outer belt. We conclude that the G₁₂ photometric parameter cannot be used in determining taxonomic complex for individual asteroids, but it can be utilized in the statistical treatment of asteroid families and different regions of the main asteroid belt.  相似文献   

Sedimentology,palaeoenvironments and biostratigraphy of the Pliocene–Pleistocene carbonate platform of Grande‐Terre (Guadeloupe,Lesser Antilles forearc)     

JEAN‐JACQUES CORNÉE  JEAN‐LÈN LÉTICÉE  PHILIPPE MÜNCH  FRÉDÉRIC QUILLÉVÉRÉ  JEAN‐FRÉDÉRIC LEBRUN  PIERRE MOISSETTE  JUAN‐CARLOS BRAGA  MIHAELA MELINTE‐DOBRINESCU  LYVANE DE MIN  JULIEN OUDET  AURAN RANDRIANASOLO 《Sedimentology》2012,59(5):1426-1451

Pliocene and Pleistocene deposits from Grande‐Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation controlled by both rapid sea‐level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 (‘Calcaires inférieurs à rhodolithes’) deposited during the Late Zanclean to Early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal‐rich deposits, which dominate the western part of Grande‐Terre, change to planktonic foraminifer‐rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 (‘Formation volcano‐sédimentaire’, ‘Calcaires supérieurs à rhodolithes’ and ‘Calcaires à Agaricia’) was deposited during the Late Piacenzian to Early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal‐dominated ramp that changes upward into a homoclinal, coral‐dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea‐level fall. Finally, Sequence S4 (‘Calcaires à Acropora’) probably formed during the Calabrian, developing as a coral‐dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in Late Calabrian times.  相似文献   

Seismic evidence of up to 200 m lake‐level change in Southern Patagonia since Marine Isotope Stage 4     

ANDREA CATALINA GEBHARDT  CHRISTIAN OHLENDORF  FRANK NIESSEN  MARC DE BATIST  FLAVIO S. ANSELMETTI  DANIEL ARIZTEGUI  PIERRE KLIEM  STEFAN WASTEGÅRD  BERND ZOLITSCHKA 《Sedimentology》2012,59(3):1087-1100

Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south‐eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80 m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo‐shorelines indicating a stepwise water‐level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake‐level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33 m below present‐day lake level point towards a long period of lake‐level highstand between roughly 53·5 ka cal. bp and 30 ka cal. bp with a maximum lake level some 200 m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30 ka cal. bp and 6750 yrs cal. bp . Dryer conditions during the Mid‐Holocene are evidenced by a dropping lake level, resulting in a basin‐wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5·8 to 5·4 ka cal. bp and ca 4·7 to 4 ka cal. bp with palaeo‐shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions.  相似文献   

Optical dating of relict sand wedges and composite-wedge pseudomorphs in Flanders, Belgium     

JAN-PIETER BUYLAERT  GUNTHER GHYSELS  REW S. MURRAY  KRISTINA J. THOMSEN  DIMITRI VANDENBERGHE  FRANS DE CORTE  IRENÉE HEYSE  PETER VAN DEN HAUTE 《Boreas: An International Journal of Quaternary Research》2009,38(1):160-175

We report on quartz Optically Stimulated Luminescence (OSL) dating of the infill of 14 relict sand wedges and composite-wedge pseudomorphs at 5 different sites in Flanders, Belgium. A laboratory dose recovery test indicates that the single-aliquot regenerative-dose (SAR) procedure is suitable for our samples (measured to a given dose ratio 0.980 ± 0.005; n =139). Completeness of resetting of the wedge infill of two samples was confirmed by single-grain analyses. The suite of optical ages indicates that repeated thermal contraction cracking, degradation and infilling with wind-blown sediment appear to have been commonplace in Flanders during the Late Pleniglacial (Oxygen Isotope Stage 2; OIS2); more specifically, around the Last Glacial Maximum (LGM, ∼21 kyr ago) and the transition period between the LGM and the start of the Lateglacial (∼15 kyr ago). Optical dating at one site has revealed two significantly older wedge levels, the younger inset into the older; the younger wedge has an age of 36 ± 4 kyr (Middle Pleniglacial; OIS3), the older wedge 129 ± 11 kyr, which points to formation during the Late Saalian (OIS6). Our OSL ages of the wedges and host sediments bracket formation of the BGB (Beuningen Gravel Bed: a widespread deflation horizon in northwestern Europe) at between ∼15 and 18 kyr; this is in good agreement with previous OSL dating studies. We conclude that optical dating using quartz SAR OSL establishes an absolute chronology for these periglacial phenomena and allows secure palaeoenvironmental reconstructions to be made.  相似文献   

Environmental history of southern Patagonia unravelled by the seismic stratigraphy of Laguna Potrok Aike     

FLAVIO S. ANSELMETTI  DANIEL ARIZTEGUI†  MARC DE BATIST‡  A. CATALINA GEBHARDT§  TORSTEN HABERZETTL¶  FRANK NIESSEN§  CHRISTIAN OHLENDORF  BERND ZOLITSCHKA 《Sedimentology》2009,56(4):873-892

Laguna Potrok Aike, located in southernmost Patagonia (Argentina, 52°S) is a 100 m deep hydrologically closed lake that probably provides the only continental southern Patagonian archive covering a long and continuous interval of several glacial to interglacial cycles. In the context of the planned ‘International Continental Scientific Drilling Program’ initiative ‘Potrok Aike Maar Lake Sediment Archive Drilling Project’, several seismic site surveys that characterize in detail the sedimentary subsurface of the lake have been undertaken. Long sediment cores recovered the material to date and calibrate these seismic data. Laguna Potrok Aike is rimmed steeply, circular in shape with a diameter of ∼3·5 km and is surrounded by a series of subaerial palaeoshorelines, reflecting varying lake-level highstands and lowstands. Seismic data indicate a basinwide erosional unconformity that occurs consistently on the shoulder of the lake down to a depth of −33 m (below 2003 ad lake level), marking the lowest lake level during Late Glacial to Holocene times. Cores that penetrate this unconformity comprise Marine Isotope Stage 3-dated sediments (45 kyr bp ) ∼3·5 m below, and post-6800 cal yr bp transgressional sediments above the unconformity. This Middle Holocene transgression following an unprecedented lake-level lowstand marks the onset of a stepwise change in moisture, as shown by a series of up to 11 buried palaeoshorelines that were formed during lake-level stillstands at depths between −30 and −12 m. Two series of regressive shorelines between ∼5800 to 5400 and ∼4700 to 4000 cal yr bp interrupt the overall transgressional trend. In the basin, mound-like drift sediments occur after ∼6000 cal yr bp, documenting the onset of lake currents triggered by a latitudinal shift or an increase in wind intensity of the Southern Hemispheric Westerlies over Laguna Potrok Aike at that time. Furthermore, several well-defined lateral slides can be recognized. The majority of these slides occurred during the mid-Holocene lake-level lowering when the slopes became rapidly sediment-charged because of erosion from the exposed shoulder sediments. Around 7800 and 4900 cal yr bp , several slides went down simultaneously, probably triggered by seismic shaking.  相似文献   

排水粉喷桩加固软土地基桩周土体强度变化规律          下载免费PDF全文

杜广印  刘松玉 《水文地质工程地质》2010,37(3):87-91

排水粉喷桩(2D工法)是同时采用粉喷桩和塑料排水板加固软土地基的一种新工法。在某高速公路中进行了排水粉喷桩加固软土地基的现场试验段施工,分别采用静力触探试验、十字板剪切试验等方法测定加固前及其加固后不同龄期的粉喷桩桩周土强度,得到了施工后桩间土强度变化的规律。测试结果表明采用粉喷桩联合排水板法加固后,桩周土强度有一个先降低后提高的过程,28天龄期时恢复到原状土强度,随着龄期的增长桩周土强度可以进一步增加。最后对桩周土强度的变化机理进行了初步探讨。  相似文献   

Lithology and palynology of Weichselian alluvial fan deposits near Eerbeek, The Netherlands     

JAAP J. M. VAN DER MEER  RUUD T. SLOTBOOM  IRENE M. E. DE VIRES-BRUYNSTEEN 《Boreas: An International Journal of Quaternary Research》1984,13(4):393-402

In a sandpit in an alluvial fan in the central Netherlands, four interstadials could be recognized. The upper two are ¹⁴C-dated and assigned to Hengelo and Moershoofd, while the lower two belong to either Odderade or Brorup. Lithological evidence suggested the existence of two zones indicative of permafrost separated by a zone in which running water was more important. The lower permafrost zone was found to be situated between the Moershoofd and Odderade interstadials, the younger zone to belong to the Upper Pleniglacial.  相似文献   

The divergence of the turbulent diffusion flux in the surface layer due to chemical reactions: the NO-O₃-NO₂ system     

JORDI VILÀ-GUERAU DE ARELLANO  PETER G. DUYNKERKE  PETER J. H. BUILTJES 《Tellus. Series B, Chemical and physical meteorology》1993,45(1):23-33

  相似文献   

Holocene palaeoenvironments at the timberline in the French Alps—a multidisciplinary approach     

LUCIEN TESSIER  JACQUES-LOUIS DE BEAULIEU  MICHEL COUTEAUX  JEAN-LOUIS EDOUARD  PHILIPPE PONEL  CHRISTIANE ROLANDO  MICHEL THINON  RE THOMAS  KAZIMIR TOBOLSKI 《Boreas: An International Journal of Quaternary Research》1993,22(3):244-254

An attempt is made to reconstruct the palaeoenvironmental Holocene history at the timberline on the basis of the analysis of various palaeoecological proxy indicators available on a marshy area and its surroundings in the Taillefer Massif (Isère. France). The multidisciplinary approach involves analyses of pollen assemblages. plant macrofossils, coleoptera remains. subfossil trunks extracted from lakes or peat-bogs. and charcoals derived from the surrounding soils. This enables definition of the respective roles of five forest taxa ( Pinus uncinata Mill., Pinus cembra L., Larix decidua Mill., Abies alba Mill, and Picea abies L. Karsten) in the evolution of high altitude forests during the Holocene. Pinus uncinata was present on the plateau throughout the Holocene. Larix and Pinus cembra were present only during two periods: 7500-5000 BP and 3500-2000 BP. All trees disappeared from the plateau at about 2000 BP, while, at lower altitude. Abies was replaced by Picea. The action of both climate and early human impact can explain these changes.  相似文献   

The sulfides in the garnet pyroxenite xenoliths from Salt Lake Crater, Oahu     

DE WAAL  S. A.; CALK  L. C. 《Journal of Petrology》1975,16(1):134-153

Trace amounts of sulfide, ranging from 0?06 to 0?26 volume percent, are present in the garnet pyroxenite xenoliths in nephelinebasalt at Salt Lake Crater, Oahu, Hawaii. Microscopic studyrevealed the existence of three chemically and physically distinctsulfide types, i.e. enclosed, interstitial, and vein sulfides.The enclosed sulfide forms spherical inclusions in primary pyroxene,garnet, ilmenite, and spinel. It has a bi-modal chemical character,which may be in part due to alteration of some of the enclosedsulfide grains by the nepheline basalt host magma, but moreprobably represent Cu-Ni-rich sulfide liquid coexisting withCu-rich monosulfide solid solution. The interstitial sulfideis uni-modal and occurs in the interstices of the primary silicates.It has been subjected to intense chemical alteration by thenepheline basalt host magma. As a result the interstitial sulfidebecame Cu-poor with a varying Ni content, which indicates thatcomplete chemical equilibrium with the basalt host magma hasnot been attained. The vein sulfide, present as fracture fillings, is of late genesisand appears to represent partly altered enclosed sulfide. Thealteration process is the same as that which affected the interstitialsulfide. The mineralogy and chemistry of the enclosed sulfide suggeststhat the xenoliths have been abruptly cooled from about 1000?C, which represents the ejection of the xenoliths from thehost basalt magma.  相似文献