The vegetation and climate of northwest Iberia over the last 14,000 years

A new pollen record from an upland lake in north-west Spain, Laguna de la Roya, spans the last ca 14,500 yrs and includes clear evidence of a Weichselian Lateglacial event correlative with the Younger Dryas. Pollen-climate response surfaces have been used to make quantitative reconstructions of palaeoclimate conditions at this and two other sites in the region. These reconstructions indicate that the climate was dry and cool during both the Late Weichselian and the Younger Dryas; in contrast, conditions during the Lateglacial Interstadial were relatively moist. During the early Holocene the climate was more continental in character than it has been for the last three millenia. Human activity has had a substantial impact upon the upland vegetation around Laguna de la Roya only during the last two millennia.     

Career Migration as Personal Biography: New Zealand Case Studies

The paper is based on autobiographical details of residential mobility for a small sample of New Zealand male career professionals collected in 1981. Classified by cohort and employment sector, the information is used to examine migration in the context of personal career development. Aspects explored include age of entry to the workforce, frequency of movement, migration and career promotion, and the spatial structure of migration. Also discussed, in conclusion, is the impact on career-related migration of the surge of national economic restructuring initiated in 1984.     

Observation bias correction with an ensemble Kalman filter

This paper considers the use of an ensemble Kalman filter to correct satellite radiance observations for state dependent biases. Our approach is to use state-space augmentation to estimate satellite biases as part of the ensemble data assimilation procedure. We illustrate our approach by applying it to a particular ensemble scheme—the local ensemble transform Kalman filter (LETKF)—to assimilate simulated biased atmospheric infrared sounder brightness temperature observations from 15 channels on the simplified parameterizations, primitive-equation dynamics (SPEEDY) model. The scheme we present successfully reduces both the observation bias and analysis error in perfect-model simulations.     

Sediment generation and soil mound denudation in areas of high-density tree throw along a river valley in the Jura Mountains,Switzerland

A preliminary field-based investigation was undertaken in a small(<10 km²)river valley located in the mountainous Jura region of northwest Switzerland.The aims of the work were to assess sediment generation and annual sediment transport rates by tree throw on forested hillslopes,and to document surface hydrology characteristics on four fresh soil mounds associated with recent tree throws over a 24-day monitoring period.For the soil mounds,average sediment recovery ranged from 7.7-28.2 g(dry weight),equivalent to a suspended sediment concentration of 145.2-327.8 g L^-1,and runoff coefficients ranged from 1.0%-4.2%.Based on a soil bulk density value of 1,044 kg m^-3,upslope runoff generation areas were denuded by an average 0.14 mm by the end of the 24-day monitoring period,representing an erosion rate equivalent to 2.1 mm yr^-1.A ca.50 cm high soil mound could therefore feasibly persist for around 200-250 years.For tree throw work,the dimensions of 215 individual tree throws were measured and their locations mapped in 12 separate locations along the river valley representing a cumulative area equivalent to 5.3 ha(av.density,43 per ha).Tree throws generated a total of 20.1 m³ of fine-sediment(<2 mm diameter),or the equivalent of 3.8×10^-4 m³ m^-2.The process of tree throw was originally attributed to two extreme weather events that occurred in west and central Europe in late December 1999.Taking the 18-year period since both storms,this represents an annual sediment transport rate of 2.7×10^-5 m³ m^-1 yr^-1.Exploring the relationship with wind on fall direction,65.5%of tree throws(143)generally fell in a downslope direction irrespective of hillslope aspect on which they were located.This infers that individual storms may not have been responsible for the majority of tree throws,but instead,could be associated with root failure.Given the high density of tree throws and their relative maturity(average age 41 years),we hypothesise that once trees attain a certain age in this river valley,their physiognomy(i.e.height,mass and centre of gravity)compromises their ability to remain securely anchored.We tentatively attribute this possibility to the presence of bedrock close to the surface,and to the shallow soil profile overlaying steep hillslopes.     

Chromian Spinel-Silicate Chemistry in Ultramafic Rocks of the Jijal Complex, Northwest Pakistan

The approximately 150 km² Jijal complex occupies a deep-levelsection of the Cretaceous Kohistan are obducted along the Indussuture. The complex consists of mafic garnet granulites, anda > 10 km ? 4 km slab of pyroxenites (diopsidite > websterite;? olivine), dunite, and subordinate peridotite, all of whichare devoid of plagioclase. These contain chromite either inlenses, layers, and veins or as disseminated grains. The chromiteis mostly medium grained, subhedral to euhedral, shows pull-aparttexture, and may contain inclusions of associated silicates.Chromite grains within thin sections of chromitite are generallyhomogeneous in composition, but dunite and pyroxenite samplescommonly contain chromite grains of variable composition. Thesegregated chromite has higher Cr₂O₃ wt%, cr-number, and mg-number,and lower fe'-number than the accessory chromite. These variationsare mainly attributed to subsolidus exchange of Mg and Fe betweenchromite and associated olivine or pyroxene, and to inheritancefrom a magmatic source, but other factors may also be responsible.In general, the chromite grains are altered along margins andfractures to ferritchromit that is enriched in cr-number (andgenerally Fe³⁺, Mn, and Ti) and impoverished in mg-number comparedwith the parent grains. Chromian chlorite (clinochlore, penninite,with up to 7?3 wt.% Cr₂O₃) is commonly associated with the alteration,as is serpentine in most silicate rocks and some chromitites.The chlorite shows considerable compositional variation fromgrain to grain and in some cases within a single grain. Clinopyroxene is low-Al, -Na and high-Ca diopside. Orthopyroxeneranges from En₉₁ to En₈₂ and olivine from Fo₉₈ to Fo₈₄ (ignoringone analysis each). The mg-number of these minerals is higherin chromitites than in dunites and pyroxenites. Several aspectsof the petrogenesis of the ultramafic rocks (e.g., the abundanceof diopsidite) are not clear, but they seem to have passed througha complex history. The high cr-numbers (>60) in the chromiteindicate that the rocks may have originated from some form ofoceanic lithosphere-island are interaction. Petrography andmineral compositional data suggest that the rocks are ultramaficcumulates derived from an are-related (?primitive) high-Mg tholeiiticmagma, possibly at pressures in excess of 8 kb.There also aresmall ultramafic bodies in the form of conformable layers andemplaced masses within the garnet granulites. These containmagnetite and pleonaste with < 10 wt.% Cr₂O₃, and less magnesianolivine and pyroxene than the principal ultramafic mass. Thesealso have the characteristics of island are plutonic rocks,but it is not clear whether the garnet granulites constitutea continuous sequence of are cumulates with the principal ultramaficmass or the two are produced from different source magmas.     

Petrology and geochemistry of the Northwest Africa 3368 eucrite

Abstract– Analysis of the mineralogy, isotopic, and bulk compositions of the eucrite meteorites is imperative for understanding their origin on the asteroid 4 Vesta, the proposed parent body of the HED meteorites. We present here the petrology, mineral compositions, and bulk chemistry of several lithic components of the new brecciated basaltic eucrite Northwest Africa (NWA) 3368 to determine if all the lithologies reflect formation from one rock type or many rock types. The meteorite has three main lithologies: coarse‐ and fine‐grained clasts surrounded by a fine‐grained recrystallized silicate matrix. Silicate compositions are homogeneous, and the average rare earth element pattern for NWA 3368 is approximately 10× CI chondrites with a slight negative Eu anomaly. Major and trace element data place NWA 3368 with the Main Group‐Nuevo Laredo trend. High‐Ti chromites with ilmenite exsolution lamellae provide evidence of NWA 3368’s history of intense metamorphism. We suggest that this meteorite underwent several episodes of brecciation and metamorphism, similar to that proposed by Metzler et al. (1995) . We conclude that NWA 3368 is a monomict basaltic eucrite breccia related to known eucrites in texture and in mineral, bulk, and oxygen isotopic composition.     

Maribo—A new CM fall from Denmark

Abstract– Maribo is a new Danish CM chondrite, which fell on January 17, 2009, at 19:08:28 CET. The fall was observed by many eye witnesses and recorded by a surveillance camera, an all sky camera, a few seismic stations, and by meteor radar observatories in Germany. A single fragment of Maribo with a dry weight of 25.8 g was found on March 4, 2009. The coarse‐grained components in Maribo include chondrules, fine‐grained olivine aggregates, large isolated lithic clasts, metals, and mineral fragments (often olivine), and rare Ca,Al‐rich inclusions. The components are typically rimmed by fine‐grained dust mantles. The matrix includes abundant dust rimmed fragments of tochilinite with a layered, fishbone‐like texture, tochilinite–cronstedtite intergrowths, sulfides, metals, and carbonates often intergrown with tochilinite. The oxygen isotopic composition: (δ¹⁷O = ?1.27‰; δ¹⁸O = 4.96‰; Δ¹⁷O = ?3.85‰) plots at the edge of the CM field, close to the CCAM line. The very low Δ¹⁷O and the presence of unaltered components suggest that Maribo is among the least altered CM chondrites. The bulk chemistry of Maribo is typical of CM chondrites. Trapped noble gases are similar in abundance and isotopic composition to other CM chondrites, stepwise heating data indicating the presence of gas components hosted by presolar diamond and silicon carbide. The organics in Maribo include components also seen in Murchison as well as nitrogen‐rich components unique to Maribo.     

Geochemistry of intermediate olivine‐phyric shergottite Northwest Africa 6234, with similarities to basaltic shergottite Northwest Africa 480 and olivine‐phyric shergottite Northwest Africa 2990

Abstract— The newly found meteorite Northwest Africa 6234 (NWA 6234) is an olivine (ol)‐phyric shergottite that is thought, based on texture and mineralogy, to be paired with Martian shergottite meteorites NWA 2990, 5960, and 6710. We report bulk‐rock major‐ and trace‐element abundances (including Li), abundances of highly siderophile elements, Re‐Os isotope systematics, oxygen isotope ratios, and the lithium isotope ratio for NWA 6234. NWA 6234 is classified as a Martian shergottite, based on its oxygen isotope ratios, bulk composition, and bulk element abundance ratios, Fe/Mn, Al/Ti, and Na/Al. The Li concentration and δ⁷Li value of NWA 6234 are similar to that of basaltic shergottites Zagami and Shergotty. The rare earth element (REE) pattern for NWA 6234 shows a depletion in the light REE (La‐Nd) compared with the heavy REE (Sm‐Lu), but not as extreme as the known “depleted” shergottites. Thus, NWA 6234 is suggested to belong to a new category of shergottite that is geochemically “intermediate” in incompatible elements. The only other basaltic or ol‐phyric shergottite with a similar “intermediate” character is the basaltic shergottite NWA 480. Rhenium‐osmium isotope systematics are consistent with this intermediate character, assuming a crystallization age of 180 Ma. We conclude that NWA 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in Mars.     

Sedimentological–ichnological model for tide‐dominated shelf sandbodies: Lower Cambrian Gog Group of western Canada

Dunes and bars are common elements in tide‐dominated shelf settings. However, there is no consensus on a unifying terminology or a systematic classification for thick sets of cross‐stratified sandstones. In addition, their ichnological attributes have hardly been explored. To address these issues, the properties, architecture and ichnology of compound cross‐stratified sandstone bodies contained in the Lower Cambrian Gog Group of the southern Canadian Rocky Mountains are described here. In these transgressive sandstones, five types of compound cross‐stratified sandstone are distinguished based on foreset geometry, sedimentary structures and internal heterogeneity. These represent four broad categories of subtidal sandbodies: (i) compound‐dune fields; (ii) sand sheets; (iii) sand ridges; and (iv) isolated dune patches; tidal bars comprise a fifth category but are not present in the Gog Group. Compound‐dune fields are characterized by sigmoidal and planar cross‐stratified sandstone in coarsening‐upward and thickening‐upward packages (Type 1); these are mostly unburrowed, or locally contain representatives of the Skolithos ichnofacies, but are intercalated with intensely bioturbated sandstone containing the archetypal Cruziana ichnofacies. Sand‐sheet complexes, also composed of compound dunes, cover more extensive subtidal areas, and comprise three adjacent subenvironments: core, front and margin. The core is characterized by thick‐bedded sets of cross‐stratified sandstone (Type 2). A decrease of bedform size at the front is recorded by wedges of thinner‐bedded, low‐angle and planar cross‐stratified sandstone (Type 3) exhibiting dense Skolithos pipe‐rock ichnofabric. The margin is characterized by interbedded sandstone and mudstone, and hummocky cross‐stratified sandstone. Sand‐sheet deposits exhibit clear trends in trace‐fossil distribution along the sediment transport path, from non‐bioturbated beds in the core to Skolithos ichnofacies at the front, and a depauperate Cruziana ichnofacies at the margin. Tidal sand ridges are large elongate sandbodies characterized by large sigmoid‐shaped reactivation surfaces (Type 4). Sand ridges display clear ichnological trends perpendicular to the axis of the ridge, with no bioturbation or a poorly developed Skolithos ichnofacies in the core, a depauperate Cruziana ichnofacies in lee‐side deposits, and Cruziana ichnofacies at the margin. While both tidal ridges and tidal bars migrate by means of lateral accretion, the latter occur in association with channels while the former do not. Because tidal bars tend to occur in brackish‐water marginal‐marine settings, their ichnofauna are typically of low diversity, representing a depauperate Cruziana ichnofacies. Isolated dune patches developed on sand‐starved areas of the shelf, and are represented by lenticular sandbodies with sigmoidal reactivation surfaces (Type 5); they typically lack trace fossils, but the interfingering muddy deposits are intensely bioturbated by a high‐diversity fauna recording the Cruziana ichnofacies. The variety of sandbody types in the Gog Group reflects varying sediment supply and location on the inner continental shelf. These, in turn, governed substrate mobility, grain size, turbidity, water‐column productivity and sediment organic matter which controlled trace fossil distribution.     

Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes

Abstract— Carbonaceous chondrites of the Ornans‐type (CO3) form a well‐documented metamorphic series. To investigate the conditions under which metamorphism took place, whole rock oxygen and carbon isotope analysis has been carried out on 10 CO3 chondrites (ALH A77307 [3.0], Colony [3.0], Kainsaz* [3.1], Felix* [3.2], Ornans* [3.3], ALH 82101 [3.3], Lancé* [3.4], ALH A77003 [3.5], Warrenton* [3.6], and Isna [3.7] [*denotes a fall]). Whole rock oxygen isotope analysis was carried out by laser‐assisted fluorination, whole rock carbon isotope analysis by continuous flow mass spectrometry. The results of this study indicate that the oxygen and carbon isotopes in CO3 finds have been significantly disturbed by terrestrial weathering processes. Conclusions based on the isotopic composition of such weathered finds may be significantly flawed. In particular, the Antarctic meteorite ALH A77307 (3.0), suggested as being close in composition to CO‐CM chondrite precursor material, has experienced significant terrestrial contamination. Oxygen isotope data for CO3 falls indicates that there is a subtle increase in Δ¹⁷O values with increasing metamorphic grade for sub‐types 3.1 to 3.4. This increase does not persist to higher sub‐types, i.e., Warrenton (3.6). These relationships are explicable in terms of the progressive formation of phyllosilicates, coupled with loss of primary phases such as melilite, and suggest that an aqueous fluid phase was present during metamorphism. Carbon abundance and δ¹³C values of CO3 falls decrease with increasing metamorphic grade. These trends reflect progressive changes in the nature of the organic macromolecular component during metamorphic heating and lend additional support to the evidence that CO3 chondrites are part of a metamorphic series. The most likely setting for metamorphism was on the CO3 parent body. The “Ornans paradox,” whereby Ornans (3.3) should belong to a higher sub‐type based on chemical compared to petrographic evidence, may result from local‐scale redox differences on the CO3 parent body. A wide variety of classification schemes have been proposed for CO3 chondrites. In view of its simplicity and applicability, the scheme of Scott and Jones (1990) is regarded as the most useful in assigning sub‐types to new CO3 samples.