Neogene Paleoseismic Events and the Shanwang Biota’s Burial in the Linqu Area, Shandong Province, China

Several paleoseismic events are recorded in the Neogene Linqu Group, exposed in the Linqu area, Shandong Province, China. The events were interpreted on the basis of fieldwork and laboratory analysis, which showed the presence of seismites with plastically deformed soft-sediment deformation structures in the Shanwang Formation, and of seismic volcanic rocks in the Yaoshan Formation which show brittle deformation. The earthquake-triggered soft-sediment deformations in the seismites include load structures, ball-and-pillow structures, flame structures, pillow-like beds, boudinage structures, slump folds, syn-depositional faults, veins of liquefied sand, and dikes of liquefied sandy lime-mud. The seismic activity is also reflected in what might be called ‘brittle seismites'; these originated when, under the influence of seismic vibrations, semi-consolidated conglomerate was shattered. Moreover, volcanic activity is related to intense earthquakes that affected basalts intercalated with sand layers; these successions are known as ‘seismic volcanic rocks', which are characterized by veins of liquefied sand intruding the basalts. All above traces of paleoseismic activity were left from one single time span of 4 Ma with active seismicity that took place 14–10 Ma. This time span is known as ‘the Linqu Neogene Paleoseismic Active Period', which is divided into four paleoseismic episodes, which were responses to tectonic extension and basin rifting in this area. It even includes the activity of the Yishu Fault Zone during the Miocene and the Neogene. The ratios of trace elements in the seismites, w(La)/w(Sc) and w(La)/w(Th) are higher than the average value of the upper crust, but w(Th)/w(Sc) is lower; this is geochemical evidence for the basin rifting that resulted in a high sedimentation rate. The intense and frequent paleo-earthquakes are held responsible for the rapid burial of the Shanwang Biota. Secondary earthquake-induced processes(e.g. slumping of a lake shore and the strongly increased lacustrine sedimentation rate) contributed to the rapid burial of the biota.     

河口海岸中长时间尺度动力地貌系统模拟研究与进展

我国河口海岸动力沉积和动力地貌研究以沉积学和地貌学的方法侧重静态描述,动力地貌相互作用的定量研究不多,与缺少动力地貌模型技术有关。本文介绍了中长时间尺度的河口海岸动力地貌模型技术及其发展和应用,讨论了决定动力地貌演变的泥沙余输运及引起泥沙余输运的主要动力因子,介绍了动力地貌模型的应用进展,进而分析了河口海岸地貌过程的机制和地貌平衡系统。本文指出对淤泥质及复杂动力条件下的河口海岸动力地貌过程还有待进一步研究。     

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

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.     

Experimental Interaction of Granitic and Basaltic Magmas and Implications for Mafic Enclaves

We have performed time series experiments for periods rangingfrom 3 min to 44 h on the interaction of granite melt and partiallymolten basalt at 920C and 10 kbar, in the presence of 5 wt.%water. With time, the assemblage of the basalt domain changesfrom predominantly amphibole+plagioclase to clinopyroxene+garnet;the melt fraction increases from {small tilde}2•5 to 40%;and between the two domains, the melt compositions progressivelyequilibrate. Initially in each run, melts of the basalt domainhave uniform plateau concentrations for SiO₂, Al₂O₃, CaO, MgO,and FeO because the activities of these components are regulatedby the mineral assemblage, but at advanced stages of reaction,no such control is evident. We have derived analytical expressionsto describe and simulate the diffusion profiles. The concentrationprofiles for SiO₂, Al₂O₃, CaO, and Na₂O in the granite, emanatingfrom the basalt–granite interface, have been used to estimateeffective diffusivities. The values from the shorter runs arecompared with those of the experiment of longest duration forwhich we assumed finite couples in our calculations. In thediffusion calculations for K₂O the difference in melt fractionbetween the two domains is accounted for. The resulting values(in cm²/s) are: D_Na2O=6 10^–7, D_K2O=3 10^–7, D_MgO=9 10^–8, D_CaO=(4–6) 10^–8, and D_SiO2 and D_Al2O3=(3–0•6) 10^–8. They are in reasonable agreement with values fromother studies. On the basis of our experiments we calculatethat mafic enclaves of magmatic origin should equilibrate toa large degree with their host magma in slowly cooling non-convectinggranitic plutons. Enclaves approaching complete re-equilibrationretain distinctly higher modal amounts of mafic minerals. Theydo not compositionally resemble binary magma mixtures, but aremore like host magma with accumulated crystals. We show thatthe modal differences between enclave and host are indicativeof the temperature of homogenization and that, in principle,this temperature can be deduced from equilibrium phase diagrams. ^* Present address: Mineralogisch-Petrologisches Institut, Universitt Gttingen, Goldschmidtstrasse 1, 3400 Gttingen, Germany     

Lateglacial and early Holocene vegetation and climate gradients in the Nordfjord–Ålesund area,western Norway

Birks, H. H. & van Dinter, M. 2010: Lateglacial and early Holocene vegetation and climate gradients in the Nordfjord–Ålesund area, western Norway. Boreas, Vol. 39, pp. 783–798. 10.1111/j.1502‐3885.2010.00161.x. ISSN 0300‐9483. Modern climate in western Norway shows a strong west–east gradient in oceanicity–continentality (coast to inner fjord) and altitudinal temperature gradients that control the regional and altitudinal zonation of vegetation. To discover if similar gradients existed during the Lateglacial and early Holocene, plant‐macrofossil analyses were made from five lacustrine sediment sequences in the Nordfjord–Ålesund region selected to sample the present climatic gradients. The macrofossil assemblages could be interpreted as analogues of the present vegetation, thus allowing reconstruction of past vegetation and climates. When the five sites were compared, climatic gradients could be detected. During the Lateglacial interstadial, mid‐alpine assemblages with Salix herbacea and S. polaris occurred at the lowland coast and upland inland sites, whereas the inland lowland site had low‐alpine dwarf‐shrub heath dominated by Betula nana, demonstrating a strong west–east gradient in temperature and precipitation and an altitudinal gradient inland. During the Younger Dryas stadial, assemblages at the lowland coast and upland inland sites resembled high‐alpine vegetation, whereas the inland lowland site was warmer with mid‐alpine vegetation, demonstrating west–east and altitudinal temperature gradients. Gradients became less pronounced in the Holocene. The early abundance of Betula nana in the inner fjord sites but its rarity at the coast is striking and reflects the oceanicity gradient. All sites became forested with Betula pubescens a few centuries into the Holocene. This forest was probably close to tree line at 370 m a.s.l. at the coast. Inland, there was no detectable altitudinal gradient, with the tree line well above 400 m a.s.l. reflecting the present pattern of tree‐line elevation.     

Aeolian construction and alluvial dismantling of a fault‐bounded intracontinental aeolian dune field (Teruel Basin,Spain); a continental perspective on Late Pliocene climate change and variability

An aeolian dune field migrating to the east encroached on the toes of alluvial fans in the Teruel Basin (eastern Spain) during a short interval in the Late Pliocene (ca 2·9 to 2·6 Ma), when Northern Hemisphere glaciation and strong glacial–interglacial cycles began. Preservation of the dune field was controlled by syn‐sedimentary activity of a normal fault. Ephemeral water discharge eroded aeolian sands and formed V‐shaped channels in which aeolian sandstone blocks accumulated. The incorporation of loose aeolian sand in wadi waters modified the sediment/water ratio, changing the physical properties of the flows as they penetrated the aeolian dune field. The erosion and cover of aeolian dune foresets by sheetflood deposits suggest that dune‐damming caused the intermittent ponding of water behind the dunes and its flashy release. The arid climate in the Late Pliocene western Mediterranean realm favoured the transport of windblown sediments from northern Africa and western Mediterranean land masses into the Mediterranean. The formation of the studied aeolian dune field (2·9 to 2·6 Ma) and possibly others (for example, the Atacama, Namib and Sahara deserts) correlates with a strong increase of the influence of obliquity, which can be attributed to the combination of a regional expression related to the reduced effect of precession due to a minimum in the long‐period (2·3 Ma) eccentricity cycle and a remote expression of the onset of the Northern Hemisphere glaciation.     

Testate amoebae as a proxy for reconstructing Holocene water table dynamics in southern Patagonian peat bogs

Testate amoebae are abundant and diverse in Sphagnum peat bogs and have been used extensively as indicators of past water table depths. Although these unicellular protists are widely dispersed with globally similar hydrological preferences, regional variations in communities demand region‐specific transfer functions. Here we present the first transfer function for southern Patagonian bogs, based on 154 surface samples obtained from transects in five bogs sampled in 2012 and 2013. Significant variance was explained by pH, electrical conductivity and, in particular, water table depth. Transfer functions for water table were constructed using weighted averaging and evaluated by cross‐validation and independent test sets. The optimal transfer function has predictive ability, but relatively high prediction errors given the wide range in sampled water tables. The use of independent test sets, as well as cross‐validation, allows a more rigorous assessment of model performance than most previous studies. For a subset of locations we compare surface and subsurface samples to demonstrate significant differences in community composition, possibly due to vertical zonation. Our results provide the first quantification of hydrological optima and tolerances for several rare species, which may include Southern Hemisphere endemics and pave the way for palaeohydrological reconstructions in southern Patagonian bogs.     

Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75°N

At the western continental margin of the Barents Sea, 75°N, hemipelagic sediments provide a record of Holocene climate change with a time resolution of 10-70 years. Planktic foraminifera counts reveal a very early Holocene thermal optimum 10.7-7.7 kyr BP, with summer sea surface temperatures (SST) of 8°C and a much enhanced West Spitsbergen Current. There was a short cooling between 8.8 and 8.2 kyr BP. In the middle and late Holocene summer, SST dropped to 2.5°-5.0°C, indicative of reduced Atlantic heat advection, except for two short warmings near 2.2 and 1.6 kyr BP. Distinct quasi-periodic spikes of coarse sediment fraction (with large portions of lithic grains, benthic and planktic foraminifera) record cascades of cold, dense winter water down the continental slope as a result of enhanced seasonal sea ice formation and storminess on the Barents shelf over the entire Holocene. The spikes primarily cluster near recurrence intervals of 400-650 and 1000-1350 years, when traced over the entire Holocene, but follow significant 885-/840- and 505-/605-year periodicities in the early Holocene. These non-stationary periodicities mimic the Greenland-[Formula: See Text]Be variability, which is a tracer of solar forcing. Further significant Holocene periodicities of 230, (145) and 93 years come close to the deVries and Gleissberg solar cycles.