The age,origin, and volcanological significance of the Y-5 ash layer in the Mediterranean

The Y-5 ash is the most widespread layer in deep-sea sediments from the eastern Mediterranean. This ash layer was previously correlated with the Citara-Serrara tuff on Ischia Island and dated at approximately 25,000 yr B.P. New data on the glass chemistry of the Y-5 ash and pyroclastic deposits from the Neopolitan volcanic province suggest that the layer is correlative with the large-volume Campanian ignimbrite and not with the deposit from Ischia Island. The volume of the Y-5 ash is approximately 65 km³ which is comparable in magnitude to the volume of the Campanian ignimbrite. An interpolated age of approximately 38,000 yr B.P. is estimated based on sedimentation rates derived from δ¹⁸O stratigraphy. There is a discrepancy between this estimate and previously reported radiocarbon ages which range from 24,000 to 35,000 yr B.P. We propose that the “Campanian tuff ash layer” should be adopted as the full stratigraphic name for the Y-5 ash. The deep-sea ash layer is divisible into two units in proximal localities, probably correlating with two major phases of the eruption: plinian and ignimbrite.     

Eastern Mediterranean sea during the last glacial maximum; an 18,000-years B.P. reconstruction

An ecological transfer function based on the distribution of planktonic foraminifera in 66 Mediterranean and 8 North Atlantic surface-sediment samples is used to estimate sea-surface temperatures and salinities for the eastern Mediterranean during the last glacial maximum (18,000 yr B.P.). The present-day distribution of planktonic foraminifera can be explained by four faunal assemblages, each of which has diagnostic environmental preferences. Factor 1 is a tropical-subtropical assemblage; factor 2 is a transitional assemblage; factor 3 is a low-salinity assemblage; and factor 4 is a subpolar assemblage. The geographic distribution of these faunal assemblages reflect the variation in overlying hydrographic conditions. The 18,000-yr B.P. samples were selected based on total faunal stratigraphy, oxygen-isotope stratigraphy, and previously determined radiometric dates for eastern Mediterranean volcanic ash layers. Estimated temperature and salinity patterns show that the greatest change between present-day and 18,000-yr B.P. sea-surface conditions existed in the Aegean Sea and immediately south of Crete. The winter temperature anomaly (18,000 yr B.P.-present) within the Aegean Sea is 6°C cooler than present. In contrast to this, the maximum summer temperature anomaly exists to the south of Crete, where sea-surface temperatures were 4°C cooler than present. Estimated sea-surface salinities also show that the greatest change took place within the Aegean Sea, being 5‰ less saline than present. The estimated temperature and salinity patterns seem to reflect changing drainage patterns during glacial times and the diversion of cool, low-salinity water into the Aegean Sea. The source of this glacial runoff appears to be large freshwater lakes that existed during this time over parts of eastern Europe and western Siberia.     

Paleoclimatic record of a long deep sea core from the eastern Mediterranean

A deep-sea core over 16 m long from the crestal area of the Mediterranean Ridge has been investigated with different techniques, including quantitative micropaleontology, stable isotopes (measured on the epipelagic species Globigerinoides ruber and on the mesopelagic species Globorotalia inflata), and clay mineralogy. The resulting record of climatic fluctuations can be cross correlated to other Mediterranean cores by means of isochronous lithologies (tephra layers and sapropels). The climatic record of the Mediterranean is similar in character, phase, and chronology to the records investigated in the equatorial Pacific and in the Caribbean. Isotope stages 1 to 17 have been recognized. Cyclically repeated stagnant cycles resulting in sapropel deposition complicate both the isotopic and the faunal signal. The isotopic investigations reveal that the temperature change in the surface layers of the eastern Mediterranean was no greater than 8°C in the late “glacial” Pleistocene. The chronostratigraphic and biostratigraphic interpretation of Core KS09 indicate that the mean sedimentation rate was 2.4 cm/1000 years, a value very close to the 2.5 cm/1000 years calculated for the entire Quaternary section at DSDP Site 125, also located in the crestal area of the Mediterranean Ridge in the Ionian Basin. The base of KS09 is likely to be very close to the Brunhes/Matuyama boundary dated at 0.7 my.     

The holstein interglaciation: Time-stratigraphic position and correlation to stable-isotope stratigraphy of deep-sea sediments

Marine molluscan shells from para-type and other loclities of the Holsteinian interglaciation were dated by Th/U and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate is corroborated by a K/Ar age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic.     

First evidence of a distal early Holocene ash layer in Eastern Mediterranean deep-sea sediments derived from the Anatolian volcanic province

A hitherto unknown distal volcanic ash layer has been detected in a sediment core recovered from the southeastern Levantine Sea (Eastern Mediterranean Sea). Radiometric, stratigraphic and sedimentological data show that the tephra, here termed as S1 tephra, was deposited between 8970 and 8690 cal yr BP. The high-silica rhyolitic composition excludes an origin from any known eruptions of the Italian, Aegean or Arabian volcanic provinces but suggests a prevailing Central Anatolian provenance. We compare the S1 tephra with proximal to medial-distal tephra deposits from well-known Mediterranean ash layers and ash fall deposits from the Central Anatolian volcanic field using electron probe microanalyses on volcanic glass shards and morphological analyses on ash particles. We postulate a correlation with the Early Holocene ‘Dikkart?n’ dome eruption of Erciyes Da? volcano (Cappadocia, Turkey). So far, no tephra of the Central Anatolian volcanic province has been detected in marine sediment archives in the Eastern Mediterranean region. The occurrence of the S1 tephra in the south-eastern part of the Levantine Sea indicates a wide dispersal of pyroclastic material from Erciyes Da? more than 600 km to the south and is therefore an important tephrostratigraphical marker in sediments of the easternmost Mediterranean Sea and the adjacent hinterland.     

Paleoclimate reconstruction based on the timing of speleothem growth and oxygen and carbon isotope composition in a cave located in the rain shadow in Israel

High-resolution ²³⁰Th/²³⁴U ages and δ¹⁸O and δ¹³C compositions of speleothems in Ma’ale Efrayim Cave located to the east of the central mountain ridge of Israel enable us to examine the nature of the rain shadow aridity during glacial and interglacial intervals. Speleothem growth occurred during marine glacial isotopic periods, with no growth during the two last marine isotope interglacial intervals and during the peak of the Last Glacial Maximum. This contrasts with speleothem growth in caves located on the western flank of the central mountain ridge, in the Eastern Mediterranean semiarid climatic zone, which continued throughout the last 240,000 yr. Thus, during glacial periods water reached both sides of the central mountain ridge. A comparison of the present-day rain and cave water isotopic compositions and amounts at the Ma’ale Efrayim Cave site with those on the western flank shows that evaporation and higher temperatures on the eastern flank are major influences on isotopic composition and the lack of rainfall. The δ¹⁸O and δ¹³C profiles of the speleothems deposited between 67,000 and 25,000 yr B.P. match the general trends of the isotopic profiles of Soreq Cave speleothems, suggesting a similar source (eastern Mediterranean Sea) and similar climatic conditions. Thus, during glacial periods the desert boundary effectively migrated further south or east from its present-day location on the eastern flank, whereas interglacial periods appear to have been similar to the present, with the desert boundary at the same position. The decrease in overall temperature and a consequent reduction in the evaporation to precipitation ratios on the eastern flank are viewed as the major factors controlling the decay of the rain shadow effect during glacial periods.     

Benthonic foraminiferal faunal and isotopic data for the postglacial evolution of the Champlain Sea

Benthonic foraminiferal faunal and isotopic data from Champlain Sea sediments (approximately 12,500 to 10,000 yr B.P. in age) in two piston cores from Lake Champlain provide a detailed, apparently continuous record of the evolution of the Champlain Sea. Cassidulina reniforme and Islandiella helenae are the dominant benthonic foraminifera during the initial phase of the Champlain Sea, and are replaced by Elphidium excavatum forma clavatum and Protelphidium orbiculare as the dominant species during the remainder of the sea's history. The oxygen-isotopic data show a gradual decrease in δ¹⁸O between approximately 12,500 and 10,900 yr B.P., followed by a more rapid decrease during the interval 10,900 to 10,000 yr B.P. The δ¹³C data have a similar trend as δ¹⁸O, with generally decreasing values up the section. The isotopic and faunal data suggest that nearly marine conditions were present in the initial plase of the Champlain Sea, followed by gradually decreasing salinities and increasing temperatures as the sea evolved. The beginning of the rapid isotopic decrease at approximately 10,900 yr B.P. marks the onset of the largest environmental change in the history of the Champlain Sea, probably reflecting a major pulse of meltwater from the Laurentide Ice Sheet.     

Middle and Late Quaternary depositional sequences and cycles in the eastern Mediterranean

Although most of the Quaternary sediments of the eastern Mediterranean appear reworked, extensive areas of hemipelagic sediments occur, mainly in the central part of the basin (Mediterranean Ridge). The most obvious character of these muddy sediments is the numerous changes in colour. They result from the organic carbon content as well as from concentration and chemical form of metallic elements (Mn, Fe, Cu, Zn). The succession of coloured layers is arranged into sequences developed between two sharp contacts; a complete sequence involves five lithofacies, from an oxidized layer at the base to a reduced sapropel at the top, and displays progressive internal changes of colour from ochre, beige, greyish-beige, grey and black layers: several sequence-variants (top-truncated, base-truncated, recurrent) are identified. These sequences are a consequence of changes in oceanographic conditions, i.e. from oxidizing to reduced environments, resulting in different organic and mineral contents. Based on detailed studies of Quaternary sediments collected by coring, a synthesized standard succession representative of the ordered sequences in the eastern Mediterranean is proposed, from about 650 000 yr as deduced from the calculated rate of sedimentation of 1·7 mm 1000yr^?1. This succession appears modulated by cyclic events: large-scale periods (200 000 yr) of reduced and oxidized sequences correlate with major alternate phases of flooding and reduced flow of the Nile River during the Quaternary. Subsequent sequences of shorter time-scale (20 000–50 000 yr) results from two factors: heaviest monsoons leading to an increase of the influx of the Nile River and global climatic changes (Eurasian ice sheet meltwater); these two factors act synchronously or independently along the studied time-span. These interplaying factors result in periodic stages of increasingly restricted conditions in the basin and explain the complexity of the eastern Mediterranean succession, at least since 650 000 yr ago.     

华北克拉通岩石圈地幔置换作用和壳幔生长耦合的Re-Os同位素证据

测定了辽宁复县奥陶纪金伯利岩和河北汉诺坝与山东栖霞第三纪碱性玄武岩中产出的地幔包体的Re Os同位素组成。金伯利岩中地幔包体的Re贫化Os同位素模式年龄 (TRD)为 2 .5～ 2 .8Ga ,从Re Os同位素定年角度证明了华北克拉通确实存在太古宙岩石圈地幔。对汉诺坝二辉橄榄岩包体获得了 (1.9± 0 .18)Ga的Re Os同位素等时线年龄 ,表明现今保存在那里的地幔主要是古元古代时形成的。汉诺坝地区出露有大量新太古代岩石 ,表明曾存在太古宙地幔。由于缺乏太古宙年龄 ,说明由汉诺坝所代表的克拉通中部曾存在的太古宙地幔在古元古代时已被减薄 ,并被 1.9Ga的新生岩石圈地幔置换。该事件与华北克拉通中部广泛的古元古代碰撞造山过程导致的麻粒岩相变质作用的时代相同 ,说明有关的岩石圈置换作用可能主要与拆沉作用有关。栖霞地幔包体具有与现代对流地幔相同的Os同位素组成 ,且Os同位素组成与Re/Os比值没有明显相关性 ,表明年龄很新。结合其它地质地球化学证据 ,说明克拉通东部的太古宙岩石圈地幔的置换作用主要发生在中生代 ,且可能与三叠纪华北和扬子陆块的陆陆碰撞造山导致的岩石圈地幔和下地壳的拆沉作用有关。本研究表明华北克拉通岩石圈地幔置换作用在时空上的分布是十分不均一的。 2 .5～ 2 .8Ga与 1.9Ga不仅?     

Identification and significance of a late Pleistocene tephra in Canterbury district,South Island,New Zealand

A rhyolitic ash 4 to 8 cm thick is well preserved within a thick loess unit in a coastal section 2 km long near Teviotdale, Canterbury district, South Island, New Zealand. The ash (informally named Tiromoana ash) contains fresh glass shards which give a fission-track age of 20,300 ± 7100 yr B.P. The only possible source for such a tephra with this age range is from Taupo Volcanic Zone (TVZ), North Island, some 550 km north of Teviotdale. Within the time span ca. 15,000 to 42,000 yr B.P. five widespread and voluminous rhyolitic tephras (viz. Rerewhakaaitu Ash, Rotoehu Ash, Kawakawa Tephra, Omataroa Tephra, and Mangaone Tephra) were erupted from TVZ. On the basis of the fission-track age, ferromagnesian mineralogy, and electron-microprobe analyses of glass shards and titanomagnetites from Tiromoana ash and the five possible correlatives listed above, Tiromoana ash is correlated with Kawakawa Tephra (dated by ¹⁴C at ca. 20,000 yr B.P.). This is the only known occurrence to date of Kawakawa Tephra in the South Island. Its preservation is attributed to special site conditions (low precipitation and minimal sheet erosion) leeward of a prominent terrace. The identification of the ash at Teviotdale as Kawakawa Tephra supports recently revised age assignments for the upper loess sheet in Canterbury. Moreover, it implies that loess enclosing Kawakawa Tephra in nonglaciated districts of southern North Island and Taupo Volcanic Zone is a correlative.     

Speleology and magnetobiostratigraphic chronology of the Buffalo Cave fossil site, Makapansgat, South Africa

Speleological, stratigraphic, paleomagnetic and faunal data is presented for the Buffalo Cave fossil site in the Limpopo Province of South Africa. Speleothems and clastic deposits were sampled for paleomagnetic and mineral magnetic analysis from the northern part of the site, where stratigraphic relationships could be more easily defined and a magnetostratigraphy could therefore be developed for the site. This is also where excavations recovered the fossil material described. A comparison of the east and South African first and last appearance data with the Buffalo Cave fauna was then used to constrain the magnetostratigraphy to produce a more secure age for the site. The magnetostratigraphy showed a change from normal to reversed polarity in the basal speleothems followed by a short normal polarity period in the base of the clastic deposits and a slow change to reversed directions for the remainder of the sequence. The biochronology suggested an optimal age range of between 1.0 Ma and 600,000 yr based on faunal correlation with eastern and southern Africa. A comparison of the magnetobiostratigraphy with the GPTS suggests that the sequence covers the time period from the Olduvai event between 1.95 and 1.78 Ma, through the Jaramillo event at 1.07 Ma to 990,000 yr, until the Bruhnes-Matuyama boundary at 780,000 yr. The faunal-bearing clastic deposits are thus dated between 1.07 Ma and 780,000 yr with the main faunal remains occurring in sediments dated to just after the end of the Jaramillo Event at 990,000 yr.     

Pollen and radiolarian records from deep-sea core RC14-103: Climatic reconstructions of northeast Japan and Northwest Pacific for the last 90,000 years

Using modern pollen and radiolarian distributions in sediments from the northwest Pacific and seas adjacent to Japan to interpret floral and faunal changes in core RC14-103 (44°02′N, 152°56′E), we recognize two major responses of the biota of eastern Hokkaido and the northwest Pacific to climatic changes since the last interglaciation. Relatively stable glacial environments (～80,000–20,000 yr B.P.) were basically cold and wet (<4°C and ～1000 mm mean annual temperature and precipitation, respectively) with boreal conijers and tundra/park-tundra on Hokkaido, and cool (<16°C) summer and cold (<1.0°C) winter surface temperatures offshore. Contrasting nonglacial environments (～10,000–4000 yr B.P.) were warm and humid (>8°C and >1200 mm mean annual temperature and precipitation, respectively), supporting climax broadleaf deciduous forest with Quercus and Ulmus/Zelkova, with surface waters in the northwest Pacific characterized by warm (>1.5°C) winter and cold (10.4°–14.3°C) summer temperatures. Climatic evidence from RC14-103 shows a high degree of local and regional variation within the context of global climatic change. Correlative ocean and land records provide the detailed input necessary to assess local/regional responses to variations in other key elements (i.e., solar radiation, monsoonal variations) of the northeast Asian climate system.     

Use of the magnetic,geochemical, and sedimentary records in establishing paleoclimate change in the environment of Sebkha: Case of the Sebkha Mhabeul in southeastern Tunisia

In this study, we explored the evidence of late Holocene climate changes in southern Tunisia, examining extreme events of flood and sandstorm sedimentary succession records, in Sebkha Mhabeul. A sediment-derived climatic proxy was inferred from a 93.5-cm-deep core (Mh1), whose dating by tephrochronology has already been achieved in previous works. Multiple geochemical, sedimentological, magnetic susceptibility, and quartz grain microtexture proxies were used to determine the shifts in regional climatic conditions. The Sebkha core captured sensitive changes in the precipitation/evaporation (P/E) balance by adjustments in salinity, and is especially valuable for reconstructing variability over centennial timescales. The Sebkha Mhabeul area showed higher salinity during the Roman Warm Period (RWP: 2100–1400 cal yr BP), the Medieval Warm Period (MWP: 1000–600 cal yr BP) and the present era, and generally lower salinity during the Dark Ages (DA: 1400-1000 cal yr BP) and the Little Ice Age (LIA: 600-200 cal yr BP).In southeastern Tunisia, the hydrological behavior was sometimes consistent with the flood activities in the eastern Mediterranean, and sometimes contemporaneous with the flood pulsations of the western Mediterranean.     

Terrestrial stable isotope records of Late Quaternary paleoclimates in the eastern Mediterranean region

Terrestrial stable isotope records (¹³C/¹²C, ¹⁸O/¹⁶O, and D/H ratios) of late Quaternary paleoclimates in the eastern Mediterranean region are reviewed. Significant paleoclimatic reconstructions come from a variety of isotopic studies. Paleogroundwaters, although they cannot be accurately dated, show oxygen and hydrogen isotopic compositions highly depleted in heavier isotopes compared to modern meteoric waters in arid regions of southern Israel, Sinai and northeastern Africa and attest to a major difference in climatic regime some time in the Pleistocene. Th-U dating of land snails showing a similar ¹⁸O depletion indicates ages of 100,000 yr and ≥300,000 yr for this climatic regime in the Negev Desert of southern Israel. Carbon isotope records of organic matter have not been studied extensively in the region, except for the record of Holocene land snails in the Negev. These document a southward shift in pure C₃ plant communities in the middle and early Holocene relative to their present distribution and indicate wetter conditions at those times. An oxygen isotope curve for the Holocene, reflecting changes in the isotopic composition of precipitation, has been established from analysis of carbonate materials—land snail shells and speleothems. The curve indicates a depletion of ca. 2‰ in ¹⁸O centered around 7000 cal yr bp, with modern levels being reached by 5000 cal yr bp. Carbon isotope analysis of soil carbonates in paleosols developed in loess in the Negev show the existence of dramatic north–south climatic gradients at the times of formation of the soils (ca. 13,000, 28,000, and ≥37,000 ¹⁴C yr bp), as occur also today due to the waning influence of Mediterranean to the south. Some isotopic methods, widely used in other regions, have received little or no attention in the eastern Mediterranean region. These include oxygen and hydrogen isotopes in wood, phosphate oxygen and organic carbon in bones and teeth, and carbon in soil organic matter.     

中国东部地幔橄榄岩捕虏体的Re-Os同位素地球化学：岩石圈地幔的形成年龄和减薄作用的制约

我国东部新生代玄武岩中包含丰富的地幔橄榄岩捕虏体，近年来一些研究者对兴蒙造山带的双辽、汪清，华北克拉通的龙岗、汉诺坝、栖霞、女山和扬子克拉通的盘石山、练山等地8个新生代玄武岩区近百个地幔橄榄岩捕虏体全岩粉末样品获得了Re-Os同位素数据，对澎湖列岛新生代玄武岩的地幔橄榄岩捕虏体中不同产状的硫化物包裹体作了原位的Re-Os同位素体系分析，此外，对辽宁复县和山东蒙阴古生代金伯利岩中的3个地幔橄榄岩捕虏体全岩粉末样品作了Re-Os分析。本文综合了文献中已有的数据，采用Re-Os同位素体系常用的方法，如Os同位素代理等时线年龄和Re亏损模式年龄，计算了SCLM的年龄。结果表明这些地区SCLM的形成年龄主要为早-中元古代，局部地区如辽宁复县有更老的年龄。我国东部新生代玄武岩中的尖晶石相地幔橄榄岩代表的SCLM主体上是元古代SCLM经过显生宙减薄作用后的残余部分，它对我国东部SCLM减薄作用在纵向上的规模和强度提供了制约。     

Distinction between the Storegga tsunami and the holocene marine transgression in coastal basin deposits of western Norway

Many coastal lakes were inundated by both the Storegga tsunami (7000 ¹⁴C yr BP) and the mid-Holocene sea-level rise (the Tapes transgression) in western Norway. The tsunami eroded lake bottoms and deposited graded and/or massive beds of sand, rip-up clasts, and coarse plant material. By contrast, when the rising sea entered the lakes, it deposited only gyttja, silt and fine sand, without causing much erosion of the underlying lake sediments. Storegga tsunami deposits in some coastal lakes were interpreted previously as ordinary marine sediments from the Tapes transgression. Our reinterpretation of these deposits shows that the transgression maximum phase was reached after 6500 yr BP, more than 1000 yr later than previously inferred for the coast of Sunnmøre. The new data cannot be combined in a shoreline diagram without showing the 6000 yr BP and 7000 yr BP shorelines as slightly warped. © 1998 John Wiley & Sons, Ltd.     

Volume partition between the plinian and co-ignimbrite air fall deposits of the Campanian Ignimbrite eruption

Summary ¶Large-scale volcanic plumes, either generated by discharge of material directly from a vent or developed from the top of pyroclastic flows, produce laterally spreading umbrella-shaped clouds that disperse pyroclastic material over large areas. During plinian eruptions followed by pyroclastic flows, an enormous quantity of ash particles produced both by sustained plumes and by the buoyant portion of pyroclastic flows settle far from the source and form widespread fall deposits. To fully evaluate the magnitude of the plinian phase for this kind of eruptions is fundamental for distinguishing between the different sources of fine ash. In this paper we demonstrate that the plinian and ignimbrite contribution to the distal ash fall can be discriminated based on thickness versus distance relationships. The Campanian Ignimbrite eruption (CI; 39,000 yr B.P.) in southern Italy, provides an important case study. This was a huge ignimbrite-forming explosive event preceded by a plinian outburst. We present a new distribution of the thick, stratified pumice fall deposit formed immediately before the emplacement of the ignimbrite and reconstruct the distribution of the CI-correlated tephra fall dispersed in eastern Europe and in the eastern Mediterranean Sea over an area exceeding 3×10⁶km². The volumes calculated for the proximal plinian, co-plinian and co-ignimbrite deposits of the CI eruption are respectively: 4km³, 16km³ and almost 100km³.Received March 3, 2002; revised version accepted June 4, 2003     

鄂尔多斯地块北部中、新生代玄武岩地球化学特征及其地质意义

通过对分布于鄂尔多斯地块北部杭锦旗与和林格尔玄武岩地球化学特征的研究,探讨了该区中、新生代岩浆源区的组成、变化及其所反映的地质意义。杭锦旗与和林格尔分别有早白垩世(Ar-Ar年龄为126.2Ma)和晚中新世(Ar-Ar年龄为6.4Ma)玄武岩分布。杭锦旗早白垩世玄武岩的SiO2(46.93%～47.93%)较低而碱含量较高(K2O+Na2O为5.75%～6.21%),组合指数σ为6.7～8.0,K2O(Na2O-2),属于碱性系列的钾质粗面玄武岩;其Mg#值为32.4～32.8,Ni、Cr含量低于20μg/g,反映玄武岩浆形成后经历过橄榄石和单斜辉石分离结晶等后期演化作用;其Nb、Ta相对于La亏损,初始87Sr/86Sr为0.7062,εNd(t)为-12.25,反映岩浆源区主要为富集EMI型地幔。和林格尔晚中新世玄武岩为橄榄拉斑玄武岩,其组合指数σ为2.1～2.8,Mg#值变化于46.7～52.4,Ni含量变化于111.1～125.8μg/g,Cr为123～178μg/g,Mg#值和Ni、Cr含量的变化反映岩浆原生程度随时间变新有所增大;其Nb、Ta相对富集,具有相似于OIB的微量元素特征,但仍表现相对富集的Sr-Nd同位素性质,初始87Sr/86Sr比值变化于0.7051～0.7053,εNd(t)为-1.91～-0.74,推测为软流圈与EMI型岩石圈地幔相互作用的产物。杭锦旗与和林格尔玄武岩的207Pb/204Pb比值都较低,△207/204为3.6～6.5,△208/20460,均具EMI型Dupal异常。玄武岩地球化学特征进一步表明,华北克拉通西部的鄂尔多斯地块所处的岩石圈自早白垩世以来发生过较小规模的伸展减薄作用,但其伸展减薄和被改造的程度远弱于华北东部。     

IODP 311航次底栖有孔虫碳稳定同位素对天然气水合物地质系统的指示

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周口店洞穴堆积物及大同火山烘烤层的热发光年龄

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