Late Glacial to Early Holocene environmental adjustment in the Mediterranean semi-arid zone of the Salines playa-lake (Alacant, Spain)

The transition from the Late Glacial to the Early Holocene in the endorheic Salines sequence, which is characterized cyclical sedimentation, occurs between 5.50 and 2.85 m depth. From 5.50-3.50 m depth the cycles are composed of a centimetre alternation of layers of dolomitic marls and gypsarenites and from 3.50-2.85 m depth by the alternation of calcitic marls and calcarenites.Pollen, biotic assemblages and geochemistry provide evidence of a gap with respect to the new hydrological conditions that characterized the beginning of the Holocene. Mesic pollen taxa increased their percentages at the beginning of the Holocene, indicating climate improvement, which coincides with the 14C radiocarbon age of 10,000 years BP. The first biotic remains (gastropods, ostracods and foraminifers) found in this sequence appeared later, at 3.80 m depth, which corresponds to 9,500 years BP, whereas the mineralogical change occurred at 3.50 m depth, which corresponds to 9,000 years BP. The advanced adaptation of the vegetation and biotic aquatic assemblages with respect to the mineralogical response corresponds to a process of a gradual increase in water availability into the lacustrine system. During the Boreal, the calcitic cycles reached their maximum thickness, suggesting a more continuous water input. This assumption has also been corroborated by the expansion of the mesic pollen taxa and the occurrence of biota taxa which depend on a permanent water body for their development.The multiproxy approach in paleoclimate scenarios is an essential tool for understanding the ecosystem adjustment during climate changes. Our results demonstrate an interval of 1000 years between the vegetal and the mineralogical reaction.     

Magnetostratigraphy of Early Cretaceous Maiolica sections of the Southern Alps (Cismon and Pra da Stua, Italy)

The bottom part of the Cretaceous Cismon section in the Southern Alps was sampled for high-resolution magnetostratigraphy. Although the almost pure pelagic nannofossil limestones ( c. 90 per cent CaCO₃) of the Maiolica/Biancone Formation are extremely weakly magnetized, stepwise thermal and alternating-field demagnetization removed overprints and isolated a characteristic remanent magnetization which is interpreted as a primary magnetization. The dominant magnetic carrier mineral is magnetite; a small fraction of haematite may be present. A clear reversal pattern can be correlated unambiguously with Mesozoic polarity chrons CM10N to CM8. A less well-constrained magnetostratigraphy from the Pra da Stua section could not be directly correlated with the global polarity scale, but biostratigraphic information allows its assignment to the interval CM10-CM5. A counterclockwise rotation of 56 and a northward translation of 28 latitude for the Cismon locality since the Early Cretaceous are derived from the palaeomagnetic data, consistent with previous results from the Southern Alps. The high-resolution magnetostratigraphy of the Cismon section is used in an effort to refine the Cretaceous timescale by the combination of magnetostratigraphic and cyclostratigraphic results from the same section. The cyclostratigraphic duration estimates of chrons CM10N to CM8 are compared to their equivalents in a number of traditional timescales and found to be shorter by a factor of 1.26-2.58.     

Palaeomagnetism of Lower Cambrian sediments from the Olenek River section (northern Siberia): palaeopoles and the problem of magnetic polarity in the Early Cambrian

New palaeomagnetic data from the Lower and Middle Cambrian sedimentary rocks of northern Siberia are presented. During stepwise thermal demagnetization the stable characteristic remanence (ChRM) directions have been isolated for three Cambrian formations. Both polarities have been observed, and mean ChRM directions (for normal polarity) are: Kessyusa Formation (Lower Cambrian) D = 145°, I = -40°, N = 12, α₉₅= 12.8°; pole position: φ= 38°S, A = 165°E; Erkeket Formation (Lower Cambrian, stratigraphically highly) D = 152°, I = - 47°, N = 23, α₉₅= 6.8°; pole position: φ= 45°S, A = 159°E; Yunkyulyabit-Yuryakh Formation (Middle Cambrian) D = 166°, I = - 33°, N = 38, α₉₅= 4.6°; pole position: φ= 36°S, L = 140°E. These poles are in good agreement with the apparent polar wander path based on the bulk of existing Cambrian palaeomagnetic data from the Siberian platform. In Cambrian times, the Siberian platform probably occupied southerly latitudes stretching from about 35° to 0°, and was oriented 'reversely' with respect to its present position. Siberia moved northwards during the Cambrian by about 10° of latitude. This movement was accompanied by anticlockwise rotation of about 30°. The magnetostratigraphic results show the predominance of reversed polarity in the Early Cambrian and an approximately equal occurrence of both polarities in the part of the Middle Cambrian studied. These results are in good agreement with the palaeomagnetic polarity timescale for the Cambrian of the Siberian platform constructed previously by Khramov et al. (1987).     

北京地区历史早期人地关系研究的重大成果——《北京历史地图集二集》评介

一部反映北京地区历史早期人类活动与自然环境的地图集《北京历史地图集二集》于1997年2月由北京出版社出版。该图集由我国著名历史地理学家侯仁之教授主编。无论从北京地区历史地理研究还是从历史地理学的学科角度看,该图集都有许多特点、贡献和作出了有益的探索。     

Oligocene to Early Miocene sedimentation and tectonics in the southern part of the Calabrian-Peloritan Arc (Aspromonte, southern Italy): a record of mixed-mode piggy-back basin evolution

The Calabrian-Peloritan Arc (southern Italy) represents a fragment of the European margin, thrusted onto the Apennines and Maghrebides during the Europe-Apulia collision in the late Early Miocene. A reconstruction of the pre-Middle Miocene tectono-sedimentary evolution of the southern part of the Calabrian-Peloritan Arc (CPA) is presented, based on a detailed analysis of the Stilo-Capo ?Orlando Formation (SCO Fm). Deposition of the SCO Fm occurred in a series of mixed-mode piggy-back basins. Basin evolution was controlled by two intersecting fault systems. A NW-SE oriented system delimited a series of sub-basins and fixed the position of feeder channels and submarine canyons, whereas a NE-SW oriented system controlled the axial dispersal of coarse-grained sediments within each of the sub-basins. From base to top, sedimentary environments change from terrestrial and lagoonal to upper bathyal over a timespan of approximately 12 Myr (late Early Oligocene-late Early Miocene). During this interval, extensional tectonic activity alternated with oblique backthrusting events, related to dextral transpression along the NW-SE oriented faults. This produced a characteristic pulsating pattern of basin evolution. Oligocene-Early Miocene evolution of the W. Mediterranean basin was dominated by ‘roll back’ of the Neotethyan oceanic lithosphere. Considerable extension in the overriding European Plate gave rise to the formation of a back arc-thrust system. The initial stages of Calabrian Basin evolution are remarkably similar to the evolution of rift basins in the back arc (Sardinia). The Calabrian basins, which are inferred to have originated as thin-skinned pull-apart basins, were subsequently incorporated into the Apennines-Maghrebides accretionary wedge by out-of-sequence thrusting, and became decoupled from the back arc. Periodic restabilization of the accretionary wedge, resulting in an alternation of backthrusting and listric normal faulting, provides an explanation for the structural evolution of these mixed-mode basins. The basins of the southern part of the CPA may be termed ‘spanner’ or ‘looper’ basins, in view of their characteristic pulsating structural evolution, superimposed upon their migration toward the foreland. This new term adequately accounts for the occurrence of tectonic inversions in long-lived piggy-back basins, as expected in the light of the dynamics of accretionary wedges.     

Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: microfossil (thecamoebian and pollen) evidence

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world’s largest freshwater resources.     

Tectonic activation,source area stratigraphy and provenance changes in a rift basin: the Early Cretaceous Tucano Basin (NE‐Brazil)

Changes in sandstone and conglomerate maturity in tectonically active basins can be considered either as the product of climatic change or of tectonic restructuring of the feeder drainage system. Besides these regional controls, changes in the configuration of local sources can expressively affect basin fill composition. The Early Cretaceous fluvial successions of the Tucano Basin, a rift basin in northeastern Brazil related to the South Atlantic opening, contain one such case of abrupt change in maturity, marked by the passage from pebbly sandstone and conglomerate rich in quartz and quartzite fragments (Neocomian to Barremian São Sebastião Formation) to more feldspathic pebbly sandstone and conglomerate bearing pebbles of varied composition (Aptian Marizal Formation). Systematic analysis of stratigraphic and spatial variation in palaeocurrents and composition of pebbles and cobbles from both units, integrated with the recognition of fluvial and alluvial fan deposits distribution, revealed an abrupt decrease in maturity during the passage from the São Sebastião Formation to the Marizal Formation. This change is explained by exhumation of basement rocks and erosional removal of originally widespread Silurian to Jurassic sandstone and conglomerate units which were a major source of reworked vein quartz and quartzite pebbles to the São Sebastião Formation. Basin border faults activation during the deposition of the Marizal Formation caused adjacent basement uplift above the local erosional base level at the basin borders, whereas during the São Sebastião Formation deposition, the basin border fault scarps probably exposed mineralogically mature sedimentary units. The proposed model has important implications for interpreting changes in sediment maturity in rift basin successions, as similar results are expected where activation of basin border faults occurs after the erosional removal of older sedimentary or volcanic units that controlled syn‐rift successions composition.     

Early Holocene environment on Bjørnøya (Svalbard) inferred from multidisciplinary lake sediment studies

Bjørnøya, a small (178 km²) island situated between the mainland of Norway and southern Spitsbergen, provides the opportunity for the reconstruction of early Holocene terrestrial and limnic palaeoenvironments in the southwestern Barents Sea. The AMS ¹⁴C dating technique, geochemical, mineral magnetic, micro and macrofossil analyses were applied to sediments recovered from lake Stevatnet and the results are interpreted in terms of palaeoenvironmental conditions between 9800 and 8300 ¹⁴C bp. After the disappearance of local glaciers before ca 9800¹⁴C BP, the lake productivity increased rapidly at the same time as pioneer plant communities developed on soils which gradually became more stable. Insect data indicates that strong seasonal contrasts with mean July temperatures around 9°C and mean January temperatures around −12°C prevailed between 9500 and 8300 ¹⁴C BP. These high summer temperatures, possibly as much as 4-5°C higher than the present, favoured the development of a flora including Dryas and Angelica cf. archangelica . The enhanced freeze/thaw processes led to an increased erosion of minerogenic and organic material. After 8000 ¹⁴C BP the temperatures may have gradually declined. The environmental reconstruction derived from our data set supports the conceptual insolation model which proposes maximum Holocene seasonality for the Northern Hemisphere at ca 9000 ¹⁴C BP.     

Early Holocene Tree Growth at a High Elevation Site in the Northernmost Scandes of Sweden (Lapland): A Palaeobiogeographical Case Study Based on Megafossil Evidence

The paper focuses on early Holocene tree growth and alpine tree-limits in the northernmost Swedish Scandes (Lapland). Megafossil wood remnants in peats and lakes were searched for over a large area at elevations high above the modern tree-limits. Wood of Pinus sylvestris, Betula pubescens spp. tortuosa and Alnus incana was discovered near the shore of a small lake (999 m a.s.l.) c. 500 m higher than today's tree-limit of Pinus sylvestris in this region. Radiocarbon dating yielded values of unprecedented age, c. 8500–8100 ¹⁴C years BP for all three species and in addition 5400–4500 ¹⁴C years BP for Betula and Alnus. The highest position of the Pinus tree-limit occurred during the early Holocene, which compares well with the situation reconstructed by megafossils in the southern Scandes. It now appears that the long-term tree-limit and climate histories are broadly the same in entire mid- and northern Fennoscandia. Corrected for glacio-isostatic land uplift, the tree-limit record suggests that the summers were c. 2.4°C warmer than today at 8500 ¹⁴C years BP . A dry continental climate with substantial seasonal contrasts is likely to have prevailed during this period, which restricted the occurrence of glaciers and glacier activity. Most circumstances point to the overriding importance of the Milankovitch orbital theory for pacing or forcing the long-term postglacial climate change. The results are inconsistent with most inferences based on pollen, certain macrofossil records and general circulation simulations. These proxy environmental histories have frequently advocated a mid-Holocene thermal optimum and an oceanic and humid climate in northern and western Fennoscandia during the early Holocene. The uncovered discrepancy between the outcome of the objective and factual megafossil method and more subjective/inferential microfossil methods should be important for Quaternary plant ecology in general, stressing the usefulness of megafossil studies.     

An Alpine Lacustrine Record of Early Holocene North American Monsoon Dynamics from Dry Lake, Southern California (USA)

Dry Lake (2763 m), located in the San Bernardino Mountains of southern California, USA, provides a high-resolution climate record from the coastal southwest depicting early Holocene terrestrial climate. 27 AMS ¹⁴C dates and multi-proxy analyses, including magnetic susceptibility, total organic mater, microfossil counts, and grain size, suggest the early Holocene was significantly wetter then present, due to an enhanced North American Monsoon (NAM). Elevated insolation at 9000 cal year B.P., raised summer sea surface temperatures in the Gulf of California and the eastern tropical Pacific, as well as land surface temperatures, extending the NAM into southern California. The data also provide evidence of the 8.2 ka event, which registers as a 300-year cool period characterized by reduced monsoonal precipitation, depressed basin productivity, and increased erosion. We suggest this event is the most likely period for the early to middle Holocene (9000–5000 cal year B.P.) glacial advance in the San Bernardino Mountains proposed by Owen et al. (2003, Geology 31: 729–732).     

New Early Cretaceous palaeomagnetic pole from Córdoba Province (Argentina): revision of previous studies and implications for the South American database

A continental sequence of red beds and interbedded basaltic layers crops out in the Sierra Chica of Córdoba Province, Argentina (31.5°S, 64.4°W). This succession was deposited in a half-graben basin during the Early Cretaceous. We have carried out a palaeomagnetic survey on outcrops of this basin (147 sites in seven localities). From an analysis of IRM acquisition curves and detailed demagnetization behaviour, three different magnetic components are identified in the volcanic rocks: components A, B and X are carried by single- or pseudo-single-domain (titano) magnetite, haematite and multidomain magnetite, respectively. Component A is interpreted as a primary component of magnetization because it passes conglomerate, contact, tilt and reversal tests. The carrier of the primary magnetization, fine-grained (titano)magnetite, is present in basalts with a high degree of deuteric oxidation. This kind of oxidation is interpreted to have occurred during cooling. Components B and X are discarded because they are interpreted as recent magnetizations. In the sedimentary rocks, haematite and magnetite are identified as the carriers of remanence. Both minerals carry the same component, which passes a reversal test. The calculated palaeomagnetic pole, based on 55 sites, is Lat. 86.0°S, Long. 75.9°E ( A ₉₅=3.3, K =35). This palaeomagnetic pole supersedes four with anomalous positions reported in previous papers.     

Scale dependence in habitat selection: the case of the endangered brown bear (Ursus arctos) in the Cantabrian Range (NW Spain)

Animals select habitat resources at multiple spatial scales. Thus, explicit attention to scale dependency in species–habitat relationships is critical to understand the habitat suitability patterns as perceived by organisms in complex landscapes. Identification of the scales at which particular environmental variables influence habitat selection may be as important as the selection of variables themselves. In this study, we combined bivariate scaling and Maximum entropy (Maxent) modeling to investigate multiscale habitat selection of endangered brown bear (Ursus arctos) populations in northwest Spain. Bivariate scaling showed that the strength of apparent habitat relationships was highly sensitive to the scale at which predictor variables are evaluated. Maxent models on the optimal scale for each variable suggested that landscape composition together with human disturbances was dominant drivers of bear habitat selection, while habitat configuration and edge effects were substantially less influential. We found that explicitly optimizing the scale of habitat suitability models considerably improved single-scale modeling in terms of model performance and spatial prediction. We found that patterns of brown bear habitat suitability represent the cumulative influence of habitat selection across a broad range of scales, from local resources within habitat patches to the landscape composition at broader spatial scales.     

Imag(in)ing 'homeless places': using auto-photography to (re)examine the geographies of homelessness

Despite its growing popularity as a method across the social sciences, the methodological literature on auto-photography is remarkably sparse. In an effort to begin redressing this gap, this paper provides an account of the ways in which auto-photography was used to complement other research methods in a (re)examination of the geographies of homelessness. It describes how auto-photography illuminated 'hidden' spaces that do not typically feature in public (or academic) imaginations of homelessness, and provided more nuanced understandings of the use, meanings and dynamics associated with other, apparently already 'known' spaces. It concludes that whilst auto-photography presents a number of logistical and ethical challenges – particularly when used with such a vulnerable group – it is nevertheless a powerful heuristic tool.     

Li／TiS2电池中Lix（pc）yTiS2插入化合物的形成

常温二次Li/TiS_2电池放电时,阴极TiS_2可以形成一系列插入化合物,本实验研究结果发现,在不同条件下,既可以形成文献报导的Li_xTiS_2(d=6.11～6.14(?)),也会形成Li_x(pc)_yTiS_2(d=19.6;14.5(?))三元共插入化合物,TiS_2层距在这样大地膨胀下(大于原层间距1～2倍),脱插后,仍可恢复原来的结构而无严重破坏。