首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
The results of magnetic and microprobe studies of the rock sequences in the Mezmaiskaya cave at the unique multilayer Paleolithic site are discussed. The magnetic properties of rocks are analyzed for 17 layers (upwards from layer 4 to layer 1\1) dated from over 73 ka ago to recent times. The rocks of layer 1C (Early Upper Paleolithic, ∼38 ka) are found to have the highest magnetic susceptibility (K) (up to 2500 × 10−6 SI), which is related to the intensive activity of [Homo sapiens]. The minimum K corresponds to the rocks of layer 2, which is overlain by layer 1D. The sizes of magnetic grains vary throughout the rock section. The largest grains are found in the middle part of the section in the Middle Paleolithic layers 2B3, 2B2, 2B1, 2A, and 2. The superparamagnetic fraction is identified in all layers. This fact supports the view that the cave was open as early as the formation of layer 4. According to the thermomagnetic data on the saturation magnetization and the temperature curves of magnetic susceptibility, magnetite is the main carrier of the rock magnetization; some samples contain iron hydroxides. Samples with iron sulfides (pyrite) are abundant. The study of the hysteresis parameters of rocks showed that the question on whether sulfide-bearing rocks are suitable for reliable paleomagnetic determinations requires further laboratory research into the origin of magnetite in the rocks. The chemical composition of rocks composing layer 2B3 and layers 1D (∼39 ka) and 2B1 (∼45 ka), in which the presence of volcanic ash has been previously established according to the presence of volcanic glass, was determined by detailed microprobe analysis. A wide variety of chemical elements (up to 18 items) was recognized in layers 1D and 2B1. The iron, titan, chrome, manganese content, and concentrations of other components vary from grain to grain. The microprobe analysis of samples from layers 1D and 2B1 revealed a set of magnetic particles with compositions characteristic of volcanic rocks, which supports the ash origin of these layers. Layer 2B3 is established not to be volcanic ash. The results on the volcanic glass in the rocks of layers 1D and 2B1 were published by Golovanova and her colleagues in Current Anthropology in October 2010 [Golovanova et al., 2010].  相似文献   

2.
It draws much attention of scientists how early hu- mans occupy and adapt to the rigorous climate and environment at high northern latitudes in East Asia after they stepped out of Africa, passed West Asia and finally arrived in East Asia[1-4]. Reliable age determi- nations of Paleolithic sites from northeastern Asia not only help to find out the earliest occupation of early humans in this region, but also relate to the founda- tion of the overall framework of human origin and migration[1-8]…  相似文献   

3.
The study area is located at S. Agata (Gera Lario), a small center at the northern end of Como Lake, near the junction of Valchiavenna and Valtellina Valleys. This site played a strategic role since ancient times, providing the control on the communications routes to both the Como Lake and the Spluga and Septimer alpine passes. Since the end of the last century archaeological findings are reported in literature, also supported, from the early XI century, by archival documents confirming the existence of the `Olonium' settlement, an administrative and fiscal center of primary importance, as well as a parish amongst the most influential in the Como Lake area. Within an area of 45,000 m2 an electrical survey has been carried out in conjunction with magnetic and GPR investigations. These studies have indicated the presence of a number of sub-areas characterized by significant anomalies defined by the overlapping of the results obtained from two or more geophysical methods. In two of such sub-areas, excavation tests have been conducted, which have brought to light a number of archaeological findings of interest. In one of the two sub-areas, which is characterized by the superimposition of electrical and radar anomalies, a deposit of large pebbles has been found. The origin of this deposit has not been ascertained, whether it is of fluvial origin, related to the deviation of the Adda river in the Pian di Spagna region in Roman times, or it is part of reclamation works, still of Roman times, of paleolacustrine marshes. The overlapping stratigraphy, however, suggests the development of fluvial channels between Roman and Low-Medieval times. In the other sub-area, excavations were carried out on sites defined by electrical and radar anomalies, and confirmed by the results from magnetic survey. The excavations brought to light, below the fluvial deposits, a large medieval edifice, which could be identified as the S. Stefano church abandoned in 1444. The church is built on earlier structures, amongst which an apse with a single aisle has been interpreted as a paleochristian sacellum.  相似文献   

4.
The paper presents the results of experimental rock-magnetic, paleomagnetic and palynologic study of Paleolithic sediments sampled along two profiles in the Akhshtyrskaya cave, situated in the vicinity of Black Sea shore. In the upper part of profiles, some magnetite was observed; in the middle and lower parts, strongly oxidized non-stoichiometric magnetite and hematite prevail. Thin maghemite covers on the surface of fine magnetite grains are present in the majority of specimens. Natural remanence has one characteristic component (CHRM), mostly of chemical origin, although in few specimens containing magnetite it may be sedimentary. Directions of CHRM obtained by standard paleomagnetic methods revealed anomalous pattern only in layer 3/2, which is slightly older than the overlying layer 3/1 whose age was established as (35±2)×103 years BP by the U-Th method. This suggests that this paleomagnetic anomaly (PMA) can be correlated with Kargapolovo excursion dated on about (45−39)×103 years BP. In the remaining overlying and underlying layers, directions of CHRM are grouped around the present geomagnetic field. Depth distributions of scalar magnetic parameters generally coincide with the lithological division of the profiles. Palynologic study revealed the presence of 22 pollen zones. Five thermomers separated with colder periods were found in the middle and lower parts of profile. The non-magnetite composition of magnetic fraction of the majority of studied sediments — oxidized nonstoichiometric magnetite and hematite — resulted in the lack of correlations between paleoclimatic and scalar magnetic characteristics.  相似文献   

5.
Foundation soil of the proposed fertiliser complex in Northern India is examined for its susceptibility to liquefaction during an earthquake. Information on geotectonic set up and earthquake occurrences in the region around the site is used for defining the earthquake parameters of the ground motion. The effective peak ground acceleration for the site is estimated to be of the order of 0.15 g. Laboratory tests were carried out on soil samples obtained from the site on a horizontal vibration table. The test results were used in determining the possibility of liquefaction employing the methodology developed at the Department of Earthquake Engineering, University of Roorkee. About 10 m of a thick soil layer below the top 1.5 m stiff clay is likely to liquefy. Remedial measures used at the site to counter the possibility of liquefaction are mentioned.  相似文献   

6.
Paleomagnetic studies of Quaternary deposits from the Malyi Kut rock sequence (Krasnodar krai, western part of the Taman Peninsula) in two time intervals of Late Pleistocene are carried out. The Malyi Kut sequence is a marine terrace of the Baku age, which is embedded in the disturbed marine Sarmatian deposits. The terrace of the Bakinian age nests the Karangat marine terrace. The presence of the marine molluscan fauna in the both terraces enables reliable dating of the studied deposits. The composition, grain size, and concentration of ferromagnetic fraction present in the studied rocks are investigated by a set of rock magnetic methods. The directions of natural remanent magnetization (NRM) are studied, and the reliability of their isolation is estimated. The results are compared with the paleomagnetic records of NRM in the rocks of the parallel coeval sections of the Tuzla (Taman Peninsula) and Roxolany (Ukraine). This correlation suggests that the studied rock sequences recorded the Mono Lake geomagnetic excursion.  相似文献   

7.
Ten thousands of bone fragments were recovered from the Ma’anshan Paleolithic site, of which 4358 pieces can be identified to skeletal elements or species. In this research, the bone assemblages are quantified based on elements of MNI, MNE, and MAU. Then bone surface modifications and skeletal element profiles of the bone assemblages are studied to understand shlepping behaviors and reveal the technique of disarticulating and defleshing the animals’ bodies, etc. Based on the analyses of bone assemblages and the comparative study with the ethnoarchaeological as well as experimental data, it is assumed that later hominids at the site made fuller use of the game animals than the earlier hominids. Incorporating the lines of evidence from chronological dating, paleoenvironment, and polished bone tools between the two cultural layers, here we propose three hypotheses suggesting that the changes of environment, the migrations of the hominids from the North, or the demographic pulses may cause such a behavioral difference. However, it is yet to be determined which hypothesis can better explain the changes.  相似文献   

8.
The prehistoric site of Ifri n'Ammar is situated in northeastern Morocco, in the northern prolongation of the Middle Atlas Mountains. It is a key location in unravelling the history of anatomically modern humans (AMH) in northern Africa as it reveals Middle and Late Palaeolithic occupation phases since ∼170 ka. Whilst the archaeological sequence within the rock shelter has been well studied, the timing of landscape dynamics around Ifri n'Ammar is still poorly understood. This study therefore aims to establish a detailed chronology of the Wadi Selloum profile at the apron of the shelter, based on optically stimulated luminescence (OSL) dating of ephemeral stream deposits. Coarse-grain quartz was used for single-grain and multiple-grain dating procedures to investigate the luminescence properties of these deposits and to get more accurate age information concerning the phases of human occupation. Continuous wave OSL (CW-OSL) revealed a dominant fast component for all quartz samples. The dose distribution of the uppermost samples showed overdispersion values >25% and significant positive skewness. We identified partial bleaching as the main source of scatter in the equivalent dose (De) distribution. The lowermost sample appeared to be close to signal saturation. The shapes of the dose response curve varied widely between aliquots and coarse quartz grains exhibited therefore very different dose saturation behaviours among aliquots. With fully saturated dose response curves (DRCs), meaningful D0 values were assumed for De estimation.The eight OSL samples yielded stratigraphically consistent ages ranging from 1.3 ± 0.2 ka to 76 ± 5 ka, thus reaching the Middle Palaeolithic period. Moreover, a pottery shard dated to 7.4 ± 0.6 ka (Early Neolithic period) by thermoluminescence (TL), perfectly matched the Holocene OSL samples extracted at the same depth of the profile. In summary, our results point to fluvial aggradation during OIS 5.1, the late glacial period, and the Holocene.  相似文献   

9.
The present paper aims to synthesize results of a systematic paleomagnetic investigation performed on metamorphic, plutonic and volcanic series from the Central Massif. Detailed, thermal and alternating field demagnetizations yield a large set of paleomagnetic directions. Several groups of directions corresponding to different age intervals are identified. The group D mean direction: D = 288°, I = 57° (37°S, 110°E), characterizes Late Devonian/Early Carboniferous metamorphic and plutonic rocks from Limousin. The group C′ directions: D = 301°, I = 24° (30°S, 79°E), represent Late Visean/Namurian magnetizations, present in the major investigated areas. The group B directions: D = 249°, I = 7° (12°N, 111°E), exist not only in the whole Central Massif, but also in other Paleozoic outcrops of the Variscan belt. They were acquired during the Namurian/Westphalian. The group A′-A directions are the only typically “European” magnetic directions. They have taken place in Stephanian/Autunian times, mainly during the Kiaman reversed interval. Interpretation of these directions in terms of geodynamics leads to a probable large S-N drift of the massif during the Latest Devonian/Early Carboniferous followed by two important rotation phases, first in the Middle Carboniferous, then at the end of the Westphalian. These rotations have also affected other massifs of the Variscan belt.  相似文献   

10.
The quality factor Q as a function of frequency in an S wave range of 1–8 Hz is estimated from records of ~60 earthquakes (M w > 3.9 and source depths of 1–60 km) obtained at the Sochi seismic station at epicentral distances of less than ~300 km. Methods of Q estimation used in the paper were developed in works by Aki, Rautian, and others; they are based on the suppression of source-related and local effects in S wave spectra with the help of coda waves measured at a fixed time from the first arrival. To compensate for directivity effects, averaging was performed over the set of events whose sources were located in a wide range of back azimuths. The geometric divergence is represented as a three-segment function: 1/R, 1, and 1/√R at epicentral distances of 1/50–1/70 to 50–70 km, 50–70 to 130–150 km, and greater than 130–150 km, respectively. The geometric divergences in this model yielded the following estimates of the quality factor: Q(f) ~ 80f 0.9 with a base of 35–280 km and Q(f) ~ 110f 0.8 with a base of 60–280 km. The resulting combinations of the propagation path effects (Q and the geometric divergence) can be used for predicting strong motion parameters in the Northern Caucasus.  相似文献   

11.
The Wulanmulun site found in 2010 is an important Paleolithic site in Ordos (China), from which lots of stone and bone artifacts and mammalian fossils have been recovered. It was previously dated by radiocarbon and optically stimulated luminescence (OSL) techniques on quartz. To further confirm the reliability of the chronology constructed based on OSL ages and test the applicability of the recently developed pIRIR procedure on sediments from northern China, twenty-four sediment samples (including eolian, lacustrine and fluvio-eolian sands) from the site were determined using the multi-elevated-temperature post-IR IRSL (MET-pIRIR or pIRIR) procedure on potassium feldspar. The results show that the studied samples have two MET-pIRIR De preheat plateaus (280–320 and 340–360 °C), and the bleaching rates of the luminescence signals are associated with sample ages and stimulation temperatures. All the pIRIR ages (7–155 ka) corrected for anomalous fading and residual dose obtained after solar bleaching for 15 h are larger than the corresponding quartz OSL ages (4–66 ka) previously determined, even for the young eolian samples (<10 ka). But the corrected IRSL(50 °C) ages (6–85 ka) are broadly consistent with the quartz ages. It appears that the IRSL(50 °C) ages are more reliable, although this contradicts the previously results obtained by other people. On the other hand, we also obtained an extended age plateau between the stimulation temperatures of 50 and 290 °C in the plot of age versus stimulation temperature (A-T plot) by subtracting different residual doses obtained after different bleaching times. The reliability of the plateau ages requires further investigation. For the sediment samples from this site, quartz should be more suitable for dating than K-feldspar, and the quartz OSL ages of 50–65 ka for its cultural layer should be reliable.  相似文献   

12.
The territory of Karelia (Baltic Shield) is virtually not represented in the global paleomagnetic database for the Lower Riphean time interval (1650—1350 Ma). As regards the paleointensity H an, the huge interval 1–2 Ga in length is represented in the global paleointensity database by only eight determinations concentrated in the interval 1–1.35 Ga. The paper presents results of paleomagnetic studies of volcanic and subvolcanic rocks composing the Early Riphean Salmi Formation, which outcrops in the valley of the lower Tulemaioki River in the northern coast area of Lake Ladoga. Results of the study indicate that, in the Early Riphean time, the East European craton was located in the tropical region of the Southern Hemisphere between 15° S and 40° S. The inferred value of H an is close to the lower boundary of the interval (1.36–11.56) × 1022 A m2, encompassing previously published intensity values of the paleofield 1–1.35 Ga; this supports the hypothesis on the existence of long intervals of a lower field in the period in question [Maquoin et al., 2003].  相似文献   

13.
Based on the Anapa (ANN) seismic station records of ~40 earthquakes (MW > 3.9) that occurred within ~300 km of the station since 2002 up to the present time, the source parameters and quality factor of the Earth’s crust (Q(f)) and upper mantle are estimated for the S-waves in the 1–8 Hz frequency band. The regional coda analysis techniques which allow separating the effects associated with seismic source (source effects) and with the propagation path of seismic waves (path effects) are employed. The Q-factor estimates are obtained in the form Q(f) = 90 × f 0.7 for the epicentral distances r < 120 km and in the form Q(f) = 90 × f1.0 for r > 120 km. The established Q(f) and source parameters are close to the estimates for Central Japan, which is probably due to the similar tectonic structure of the regions. The shapes of the source parameters are found to be independent of the magnitude of the earthquakes in the magnitude range 3.9–5.6; however, the radiation of the high-frequency components (f > 4–5 Hz) is enhanced with the depth of the source (down to h ~ 60 km). The estimates Q(f) of the quality factor determined from the records by the Sochi, Anapa, and Kislovodsk seismic stations allowed a more accurate determination of the seismic moments and magnitudes of the Caucasian earthquakes. The studies will be continued for obtaining the Q(f) estimates, geometrical spreading functions, and frequency-dependent amplification of seismic waves in the Earth’s crust in the other regions of the Northern Caucasus.  相似文献   

14.
The contamination of water flow in Soldatskaya Cave is studied. Groundwater of the cave was found to feature bacterial pollution. The distribution of bacterial cells over the karst system is examined. The contamination is shown to correlate with anthropogenic load. The major hydrodynamic and physicochemical characteristics of groundwater flow are evaluated, and their correlation with self-purification is demonstrated. Components of the karst water self-purification mechanisms are analyzed. The possibility to intensify karst water self-purification is considered.  相似文献   

15.
Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper  相似文献   

16.
Diverse latest Pliocene volcanic and plutonic rocks in the north-central Caucasus Mountains of southern Russia are newly interpreted as components of a large caldera system that erupted a compositionally zoned rhyolite-dacite ash-flow sheet at 2.83 ± 0.02 Ma (sanidine and biotite 40Ar/39Ar). Despite its location within a cratonic collision zone, the Chegem system is structurally and petrologically similar to typical calderas of continental-margin volcanic arcs. Erosional remnants of the outflow Chegem Tuff sheet extend at least 50 km north from the source caldera in the upper Chegem River. These outflow remnants were previously interpreted by others as erupted from several local vents, but petrologic similarities indicate a common origin and correlation with thick intracaldera Chegem Tuff. The 11 × 15 km caldera and associated intrusions are superbly exposed over a vertical range of 2,300 m in deep canyons above treeline (elev. to 3,800 m). Densely welded intracaldera Chegem Tuff, previously described by others as a rhyolite lava plateau, forms a single cooling unit, is > 2 km thick, and contains large slide blocks from the caldera walls. Caldera subsidence was accommodated along several concentric ring fractures. No prevolcanic floor is exposed within the central core of the caldera. The caldera-filling tuff is overlain by andesitic lavas and cut by a 2.84 ± 0.03-Ma porphyritic granodiorite intrusion that has a cooling age analytically indistinguishable from that of the tuffs. The Eldjurta Granite, a pluton exposed low in the next large canyon (Baksan River) 10 km to the northwest of the caldera, yields variable K-feldspar and biotite ages (2.8 to 1.0 Ma) through a 5-km vertical range in surface and drill-hole samples. These variable dates appear to record a prolonged complex cooling history within upper parts of another caldera-related pluton. Major W-Mo ore deposits at the Tirniauz mine are hosted in skarns and hornfels along the roof of the Eldjurta Granite, and associated aplitic phases have textural features of Climax-type molybdenite porphyries in the western USA. Similar 40Ar/39Ar ages, mineral chemistry, and bulk-rock compositions indicate that the Chegem Tuff, intracaldera intrusion, and Eldjurta Granite are all parts of a large magmatic system that broadly resembles the middle Tertiary Questa caldera system and associated Mo deposits in northern New Mexico, USA. Because of their young age and superb three-dimensional exposures, rocks of the Chegem-Tirniauz region offer exceptional opportunities for detailed study of caldera structures, compositional gradients in volcanic rocks relative to cogenetic granites, and the thermal and fluid-flow history of a large young upper-crustal magmatic system.  相似文献   

17.
Water Resources - Examples are given for numerical modeling of rain-induced flash floods in mountain areas based on actual and forecast data on precipitation. The calculated hydrographs are...  相似文献   

18.
We report on the paleomagnetism of ten sites in the products of the most recent silicic eruptive cycle of Pantelleria, Strait of Sicily. Previously radiometrically dated at 5–10 ka, our comparison with proxies for geomagnetic field directions allows us to narrow considerably the time window during which these eruptions occurred. The strongly peralkaline composition causes the magmas to have low viscosities, locally resulting in strong agglutination of proximal fall deposits. This allows successful extraction of paleomagnetic directions from the explosive phases of eruptions. One of our sites was located in the Serra della Fastuca fall deposit, produced by the first explosive event of the eruptive cycle. The other nine sites were located in the most recent explosive (pumice fall and agglutinate from Cuddia del Gallo and Cuddia Randazzo) and effusive (Khaggiar lava) products. The (very similar) paleomagnetic directions gathered from eight internally consistent sites were compared to reference geomagnetic field directions of the last 5–10 ka. Directions from Cuddia del Gallo agglutinate and Khaggiar flows translate into 5.9- to 6.2-ka ages, whereas the Fastuca pumices yield a slightly older age of 6.2–6.8 ka. Hence, the most recent silicic eruptive cycle lasted at most a millennium and as little as a few centuries around 6.0 ka. Paleomagnetically inferred ages are in good agreement with published (and calibrated by us) 14C dates from paleosols/charcoals sampled below the studied volcanic units, whereas K/Ar data are more scattered and yield ∼30% older ages. Our data show that the time elapsed since the most recent silicic eruptions at Pantelleria is comparable to the quiescence period separating the two latest volcanic cycles.  相似文献   

19.
Many archaeological sites were excavated in China, but rarely in the adjacent coastal areas. An archaeological site at Huangniliang in the coastal area of Shandong Province, northern China was excavated in 2013. Abundant stone artifacts including hammers, cores, flakes, chunks, and retouched tools are found in the silty aeolian sediments. In this study, optically stimulated luminescence (OSL) technique was employed to establish the chronological framework of the site. Medium-grained (45–63 μm) quartz was extracted from six sediment samples for dating. The equivalent doses obtained with the single-aliquot regenerative-dose (SAR) protocol are shown to increase with depth. Three samples from the stone-tool containing layer yield OSL ages ranging from 54 ka to 59 ka, providing the earliest geochronological evidence for the presence of humans in the eastern coast of Shandong peninsula during the early period of Marine Isotope Stage (MIS) 3.  相似文献   

20.
A magnetic method is proposed for reconstructing the paleoclimate existing at the formation time of rocks of the Paleolithic Kostenki-12 site section. Results obtained from an experimental study of scalar magnetic characteristics (SMCs) of the rocks (magnetic susceptibility, anhysteretic remanent magnetization, and saturation isothermal remanent magnetization) are presented. These results indicate complex along-section SMC behavior distinguished by alternating larger and smaller values of the parameters. The magnetic minerals of the section are mainly represented by pseudo-single-domain magnetite grains. The size of the magnetite grains in the pseudo-single-domain range varies along the section, increasing in its lower half. The SMCs values plotted on different scales for the upper and lower halves of the section clearly revealed 12 magnetic zones (MZs). Comparison of the MZs with palynological zones obtained in a parallel section showed, on the whole, a convergence of data: MZs with larger (smaller) SMC values correlate with thermomers (cryomers). Comparison of along-section SMC variations with the GRIP (Greenland Ice Core Project) curve of the time dependence of paleotemperatures confirmed or refined the ages of lithologic horizons. As a result, it is established that constraints on paleoclimatic changes in the rock formation time can be gained from SMC variations if the main carriers of magnetization in rocks are pseudo-single-domain magnetite grains even with magnetic grain size varying along the section.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号