琼北老城剖面记录的马袅—铺前断裂西段晚更新世活动历史

马袅-铺前断裂为1605年海南琼山7.5级大地震的发震断裂之一,其活动历史研究对琼北地区地壳稳定性评价、防震减灾以及琼州海峡跨海大桥等重大工程建设有重要意义。地质地貌调查结果表明,马袅-铺前断裂西段由三条近东西向平行展布的北倾阶梯状正断层组成,并构成南北宽约2.5 km的断裂带。老城人工开挖南北宽达70 m的断裂带剖面揭露了该断裂晚更新世活动历史,道堂组光释光(OSL)年代学测试结果表明断裂在距今16~31 ka期间经历了两期活动:第一期表现为南、北相向倾斜的正断活动,累计垂直位移3.3 m;第二期为南倾的正断活动,活动强度较大。马袅-铺前断裂错断不同时代地层的位移量表明该断裂自上新世以来开始活动,第四纪活动强烈,现今仍是琼北控制地震活动的重要断裂。     

Late Pleistocene arctic fox (Alopex lagopus) from Crimea,Ukraine

The teeth and bone fragments of Alopex lagopus of early Weichselian age from Mousterian layers of grotto Prolom 2 in Crimea have been studied. The Crimean fossil arctic fox was found to be smaller than the late Weichselian subspecies, A. l. rossicus, from the East European Plain, but it seems to be similar in dimensions to the recent insular subspecies, A. l. spitzbergenensis. From the latter, the Crimean arctic fox differs in the relatively longer carnassial teeth and relatively wider m1. In the Late Pleistocene of Europe, a progressive increase in size of A. lagopus is observed, that makes it possible to recognize two subspecies, stratigraphically replacing one another. The arctic fox from Prolom 2 is presumably referable to the subspecies A. l. meridionalis, while the animals from another Crimean Upper Paleolithic site, Siuren 1, are referred to A. l. fossilis.     

晚更新世以来冲绳海槽天文驱动的气候变化: 来自CSHC-15钻孔的证据

东海冲绳海槽是一个年轻的弧后盆地,自中新世以来接受了来自长江、黄河以及陆架输送的物质,具有高沉积速率和富有机质等沉积特征,但是沉积记录的年代学约束较为薄弱,影响了对气候信号变化的解读。本研究以冲绳海槽中北部CSHC-15钻孔的60 m连续样品为对象,选取高分辨率的主微量元素含量作为古气候替代指标开展天文年代学分析,采用碳同位素测年数据和底栖有孔虫氧同位素记录作为年龄约束,建立该钻孔约200 ka以来的沉积记录变化。通过对沉积物时间域Al、K、Ti等主微量元素含量序列进行频谱分析,观察到显著的100 ka短偏心率、41 ka斜率、约23 ka岁差以及10 ka半岁差周期。由于该钻孔的底栖有孔虫种属存在差异,在没有放射性同位素年龄的约束下,氧同位素值与国际标准曲线LR04的对比结果效果不佳。因此,本研究利用La04天文轨道模型的岁差周期进行约束,进行精细的天文调谐,以获得可靠的地层年代框架;此外,结合贝叶斯统计的年龄模型分析方法,计算了该天文年代标尺的误差范围,从而进一步提高了对冲绳海槽晚更新世以来沉积记录年代的可靠性,其结果有助于深入探究气候变化和环境演化的影响。

     

辽东湾LDD7孔晚更新世以来的沉积层序与古环境演化

对取自渤海辽东湾中部LDD7孔的300个沉积物样品进行了微体古生物分析,对196个样品进行了粒度分析,并选取8个层位的底栖有孔虫混合种进行了AMS¹⁴C测年,利用线形插值方法建立了该孔的年代地层框架。研究结果表明:自晚更新以来辽东湾中部保持了相对连续的沉积序列,LDD7孔记录了该区约60.85 cal.kaBP以来的沉积环境演化过程。根据垂向上微体化石组合和岩性的变化,将全长50.1 m的沉积物柱状样划分为9个沉积单元,分别代表晚更新世冰期旋回中随着海平面的变化,辽东湾中部区域在不同阶段分别处于海相、陆相或海陆过渡相沉积环境;LDD7孔中共识别出两次主要的海侵过程,分别对应着渤海中部Bc-1孔所记录的献县海侵与黄骅海侵;此次测年结果进一步明确了辽东湾中部两次海侵持续的确切时间,分别是45.84~27.66 cal.kaBP和10.64~0 cal.kaBP。此外,几个相关岩心的年代框架计算结果表明,献县海侵过程中辽东湾南部沉积速率低于中部,而献县海侵之后辽东湾南部的沉降总量和平均沉积速率都明显高于中部。     

The First Data on Late Pleistocene Ostracods from the Kurai Depression (Gornyi Altai)

Doklady Earth Sciences - In the sections of Late Pleistocene deposits of the Kurai Depression of Gornyi Altai studied, an ostracod assemblage, including Leucocythere sp. 1, L. sp. 2, Leucocythere...     

Silicoflagellates of the middle-early Late Eocene of the Kronotskii Bay (Eastern Kamchatka)

The most complete characterization of Dictyochophyceae (silicoflagellate) assemblages from sediments of the Kronotskii Bay, Eastern Kamchatka, which are typical of the Corbisema hexacantha (Middle Eocene) and Naviculopsis foliacea (terminal middle-initial Late Eocene) zones in the tropical/subtropical zonation by Bukry (1981), is considered for the first time. In total, 43 silicoflagellate species of 8 genera are identified. The prevalence of species of the genera Corbisema and Dictyocha in the assemblages suggest warm, close to subtropical conditions in a sea basin that existed in the Eastern Kamchatka region during the Middle-Late Eocene.     

南海北部晚更新世以来的古海洋环境演化特征——来自N-31柱样的沉积记录

对南海北部N-31柱状样沉积物进行了浮游有孔虫定量分析鉴定、氧碳同位素、碳酸盐含量和粒度测试以及AMS14C测年,并采用古生态转换函数计算了表层海水古温度和温跃层深度,揭示了该海区约55 ka以来的古海洋环境特征.转换函数计算的表层海水古温度结果表明,夏季温度的变化范围为27.0～29.6℃,变化幅度为2.6℃,冬季温...     

Late Pleistocene large mammal faunas from the Urals

The 121 local faunas of large mammals from Late Pleistocene sites of the South (56–51°N), Middle (59–56°N) and North (64–59°N) Urals have been studied. All local faunas were combined into eight chronological groups on the basis of radiocarbon dates and the evolutionary level of rodents present in them. On the basis of species composition analysis of the faunas, three chronological complexes have been distinguished: Mikulino, Early–Middle Valdai and Late Valdai. The first is characterized by the presence of Hystrix vinogradovi and Ursus thibetanus; the second, by the presence of a large form of horse (Equus (E.) cf. latipes), Crocuta crocuta, Ursus spelaeus and U. savini; the third, by the presence of a small horse (E. uralensis) and absence of U. spelaeus, U. savini and C. crocuta. The latter two complexes were represented by three geographical variants: southern (South Urals), northern (North Urals) and transitional (Middle Urals). Differences between theriocomplexes are related to changes in morphology and areas and extinctions of a series of species. The existence of chronological theriocomplexes and their geographical variants was determined by chronological and geographical change in structure of paleophytocoenoses. It should be noted that the role of human in changes of chronological complexes and species extinctions in the Late Pleistocene has not been demonstrated in the Urals. In the Urals U. savini probably became extinct at the end of the Middle Valdai, C. crocuta at the beginning of the last glacial maximum (LGM), U. spelaeus at the end of the LGM, Coelodonta antiquitatis at the beginning of the Preboreal and Megaloceros giganteus at the middle of the Atlantic.     

Late Pleistocene(MIS 2) climate change on the Northern Tibetan Plateau inferred from pollen and geochemical records from Lake Gomo Co

正Introduction A 405-cm sediment section GM02 from Gomo Co salt lake in the northern Tibetan Plateau was used to reconstruct climate changes during marine isotope stage(MIS)2,including the Last Glacial Maximum(LGM)and last     

Genesis of Oils in Eastern Kamchatka: Evidence from Hydrocarbon Biomarkers

Gas chromatography and gas chromatography–mass spectrometry data on oils from wells and seeps in the Eastern Kamchatka Basin indicate that, according to their composition and the distributions of biomarker molecules, these oils can be classified into three groups, which differ in the composition of the parent organic matter, litho–facies sedimentation conditions, and catagenetic transformations. Oils from the wells were determined to be produced by organic matter of the sapropel type of marine facies in the main oil window (MC₂). Condensate from the natural seep was generated at higher catagenesis grades (MC_2–3) by organic matter of the sapropel–humus type of littoral facies. Uzon oil shows are demonstrated to be formed in a continental environment by organic matter of the humus–sapropel type and were not genetically related to oil from the Paleogene–Neogene source rocks of the Bogachevka Formation.     

Late Pleistocene climate of the northern Iberian Peninsula: New insights from palaeoglaciers at Fuentes Carrionas (Cantabrian Mountains)

New ¹⁰Be dates for glacial landforms in the Fuentes Carrionas area (Cantabrian Mountains, nothern Spain) are presented. Mapped and dated landforms in Fuentes Carrionas made possible a palaeoglacier reconstruction for four glacial stages. Results were compared to other nearby palaeoenvironmental proxies, so a final approximation on the mean annual temperature and annual precipitation that caused the four glacial advance stages is proposed. Glaciers reached their maximum extension at 36 ka, in a cold and dry environment. A second advance stage took place between 18.5 and 19.5 ka, during the Last Glacial Maximum (LGM), when glaciers advanced in a wet environment, with positive rainfall anomalies. A third glacial advance was dated during the Oldest Dryas, in which climate shifted to extremely cold and dry conditions. Finally, a last stage has been identified and proposed to the Younger Dryas, in which precipitation anomalies are negligible. Our results confirm some of the previously made palaeoglacial and palaeoenvironmental inferences for the Iberian Peninsula, as well as provide valuable and accurate anomalies, which are useful for climate modelling.     

Dated Paleontological cave sites of Central Europe from Late Middle Pleistocene to early Upper Pleistocene (OIS 5 to OIS 8)

Caves are terrestrial depositories that preserve a large variety of organic and inorganic remains. These may contain important Quaternary climatic and ecological information. Most of the faunal remains, however, cannot be linked to any Interglacial or Glacial period exclusively. Reliable dating of such remains is therefore required. Experience has, however, shown that ESR dating of speleothems or ²³⁰Th/U dating of bones are of disputable value. Only TIMS-²³⁰Th/U dating of speleothems appears to yield reliable ages. Dating the bottom and top of speleothem layers permit assigning Pleistocene faunal remains to the OIS chronology if the deposition of the speleothems and the faunal remains are clearly correlated. Care must be taken to consider the depositional situation of each site before interpreting any age dates. In this paper we present an overview of all numerically dated paleontological cave sites in Central Europe between OIS 5 and OIS 8. A total of 25 strata were dated from 13 sites, most of them deposited during OIS 5; the rest belonging to OIS 6 and 7. Numerically dated paleontological sites older than OIS 8 are not known.     

Granitization and magmatic replacement in the contact aureole of the Yurchik gabbronorite massif (Ganal Ridge, Kamchatka)

It is shown that formation of high-temperature granulite-like rocks in the contact aureole of the Yurchik gabbronorite intrusion of the Ganal Ridge in East Kamchatka was caused by contact metamorphism, metasomatism, and local melting of the primary sedimentary-volcanogenic rocks of the Vakhtalkinskaya Sequence of the Ganal Group. The temperature in the inner part of the aureole reached 700–800°C and caused transformation of basic rocks into two-pyroxene-plagioclase, clinopyroxene-amphibole-plagioclase, and amphibole-plagioclase rocks, while sedimentary rocks were replaced by garnet-biotite and garnet-cordierite-biotite hornfelses. Locally, basic volcanic hornfelses were subjected to metasomatic alteration with the formation of bodies of biotite-orthopyroxene-plagioclase metasomatites. In the zones of the most intense fluid filtration, the metasomatites experienced local magmatic replacement resulting in the formation of biotite-orthopyroxene-plagioclase ± garnet migmatite veinlets and patches. Bodies of garnet enderbites were formed after sedimentary interlayers at temperatures of 700–800°C and a lithostatic pressure of 3.2–4.8 kbar. The comparison of the chemical composition of the Vakhtalkinskaya basic volcanics and the products of their transformation indicates that, in terms of chemistry, the metasomatic alterations and magmatic replacement correspond to siliceous-alkaline metasomatism (granitization) causing a subsequent and uneven influx of Si, Al, Na, K, Rb, Ba, Zr, Nb, and Cl and removal of Fe, Mg, Mn, Ca, and some trace elements (Cr, Co, Ti, Y, and S). The processes of metamorphism and metasomatism were presumably provoked by highly mineralized mantle fluids that were filtered through magmatic channels that served as pathways for gabbroid magma.     

Morphological Chronoclines among Late Pleistocene Muskrats (Ondatra zibethicus: Muridae, Rodentia) from Northern Florida

The muskrat (Ondatra zibethicus) is presumed to have undergone a rapid phyletic size decrease near the end of the Pleistocene. Evolutionary changes in the size of middle to late Wisconsinan (ca. 32,000–12,300 ¹⁴C yr B.P.) muskrats from the Aucilla River, Jefferson County, Florida, were reconstructed by examining length and width of the lower first molar (m1). Body mass, estimated from m1 length, was relatively stable from 32,000 to 16,000 ¹⁴C yr B.P. and decreased only slightly by 12,300 ¹⁴C yr B.P. If the size trend found in the Aucilla River material is characteristic of the southeastern United States, a body size decrease after 12,300 ¹⁴C yr B.P. is needed to explain the smaller size of modern populations. It was previously thought that the length/width (l/w) ratio of the muskrat m1 was a paleoenvironmental indicator based on its presumed correlation with latitude in modern populations. We examined the length and width of modern muskrats from several geographic regions and found only a very weak trend in the size of the m1 between northern and southern populations; however, highly significant differences were found between regions of similar latitude. Our data indicate that chronoclines in the m1 of the Aucilla muskrat material and other such documented trends among fossil muskrats have paleoenvironmental significance, but it is not yet clear which environmental variables can best be predicted from them.     

A Late Pleistocene transgression in Thailand: A marine molluscan fauna from Ban Praksa (Samut Prakan Province)

A Late Pleistocene molluscan fauna sampled at Ban Praksa, near the Chao Phraya River mouth (Lower Central Plain of Bangkok, Thailand) is herein analyzed and paleoecologically characterized, revealing a shallow infralittoral, coarse/hard-bottomed environment. The comparison of the Ban Praksa association with several coeval ones recovered from Phra Pradaeng Formation seems to be evidence of a 10,000 year hiatus between two separate groups of marine faunas, possibly belonging to different interstadial transgressive peaks that occurred during the long-term sea-level regression following the Last Interglacial.     

西北冰洋阿尔法脊晚第四纪的陆源沉积物记录及其古环境意义

通过西北冰洋阿尔法脊B84A孔中—晚第四纪以来的沉积物颜色旋回,Mn、Ca元素相对含量、颜色反射率、有孔虫丰度、冰筏碎屑(IRD)含量、粒度组分及其敏感性分析的综合研究,建立了B84A孔的地层年代框架,其沉积物被划分为MIS 12～MIS 1的沉积序列。阿尔法脊B84A孔可以识别出12个IRD事件,它们大多出现在冰消期,并认为其源区为加拿大北极群岛地区。这些IRD事件反映了加拿大北极冰盖的崩塌和气候变化。阿尔法脊B84A孔沉积物的环境敏感组分分别为细组分(4～9μm)和粗组分(19～53μm),两者的变化趋势相反,主要由海冰和洋流进行搬运,指示了洋流的强度变化。B84A孔的平均沉积速率约为0.4 cm/ka,与阿尔法脊周围地区沉积速率相近。相比于近岸的高沉积速率,其限制因素主要为大面积海冰覆盖造成的较低的生产力和由于长距离搬运造成的较低的陆源输入量。     

Late Pleistocene history of the North Pacific: Evidence from a quantitative study of radiolaria in core V21-173

Objective quantitative estimates of paleo-oceanographic conditions in the North Pacific can be made by analyses of radiolarian assemblages. With appropriate computation, transfer functions developed in a study of surface sediments can be used to estimate oceanographic conditions in cores containing late Pleistocene radiolarian faunas. Analysis of core V21-173 indicates that conditions as warm as the Holocene were rare during the past 800,000 yr, and that the region experienced marked near-surface temperature drops correlative with Caribbean and continental records for the past 250,000 yr. A major world-wide warm event at about 400,000 yr is also indicated.     

Late Pleistocene and Holocene cool‐water carbonates of the Western Mediterranean Sea

Post‐glacial, neritic cool‐water carbonates of the Western Mediterranean Sea were examined by means of hydroacoustic data, sediment surface sampling and vibrocoring to unravel geometries and to reconstruct sedimentary evolution in response to the last sea‐level rise. The analysed areas, located on the Alboran Ridge, in the Bay of Oran, and at the southern shelf of the island of Mallorca, are microtidal and bathed by oligotrophic to weakly mesotrophic waters. Seasonal water temperature varies between 13 °C and 27 °C. Echosounder profiles show that the Bay of Oran and the southern shelf of Mallorca are distally steepened ramps, while the Alboran Ridge forms a steep‐flanked rugged plateau around the Alboran Island. In the three areas, an up to 10 m thick post‐glacial sediment cover overlies an unconformity. In Oran and Mallorca, stacked lowstand wedges occur in water depths of 120 to 130 m. On the Alboran Ridge and in the Bay of Oran, highstand wedges occur at 35 to 40 m. Up to 5 m long cores of upper Pleistocene to Holocene successions were recovered in water depths between 40 and 81 m. Deposits contain more than 80% carbonate, with mixed carbonate‐volcaniclastics in the lower part of some cores in Alboran. The carbonates consist of up to 53% of aragonite and up to 83% of high magnesium calcite. Radiocarbon dating of bivalve shells, coralline algae and serpulid tubes indicates that deposits are as old as 12 400 cal yr bp . The carbonate factories in the three areas are dominated mostly by red algae, but some intervals in the cores are richer in bivalves. A facies rich in the gastropod Turritella, reflecting elevated surface productivity, is restricted to the Mallorca Shelf. Rhodoliths occur at the sediment surface in most areas at water depths shallower than 70 m; they form a 10 to 20 cm thick veneer overlying rhodolith‐poor bioclastic sediments which, nonetheless, contain abundant red algal debris. This rhodolith layer has been developing for the past 800 to 1000 years. Similar layers at different positions in the cores are interpreted as reflecting in situ growth of rhodoliths at times of reduced net sedimentation. Sedimentary successions in the cores record the post‐glacial sea‐level rise and the degree of sediment exposure to bottom currents. Deepening‐upward trends in the successions are either reflected by shallow to deep facies transitions or by a corresponding change of depth‐indicative red algae. There are only weak downcore variations of carbonate mineralogy, which indicate that no dissolution or high magnesium to low magnesium calcite neomorphism occurs in the shallow subsurface. These new data support the approach of using the Recent facies distribution for interpretation of past cool‐water, low‐energy, microtidal carbonate depositional systems. Hydroacoustic data show that previous Pleistocene transgressive and highstand inner ramp deposits and wedges were removed during sea‐level lowstands and accumulated downslope as stacked lowstand wedges; this suggests that, under conditions of high‐amplitude sea‐level fluctuations, the stratigraphic record of similar cool‐water carbonates may be biased.     

晚更新世以来台湾浅滩西部地层结构与古环境演化

根据对台湾浅滩西部地质浅钻的沉积相、粒度和AMS 14C年代分析及高分辨率浅地层剖面解释,本文研究了浅滩大型沙波区的地层结构与沉积环境演化.台湾浅滩西部保存了三期海相层和两期陆相层.下部的海相层(DU6)可能形成于氧同位素5.1期,以潮间带—潮下带浅海沉积为主;中间的海相层(DU4)可能形成于氧同位素3期,以滨岸—潮间带沉积为主;上部的海相层(DU2和DU1)为形成于末次冰消期以来的海侵砂和潮流砂.两期陆相层(DU5和DU3)为沟谷充填沉积,可能形成于氧同位素4和2期.冰后期海侵过程形成的中粗砂层构成了沙波的基底部分(DU2).沙波的主体部分(DU1)形成于全新世高海平面以来,主要由中粗砂和含砾中粗砂组成.沙波的粒度频率分布曲线主要众数组分-1~3 Φ,形态尖陡;概率累积曲线多为两段式,跃移组分含量高于80%,悬移组分不足20%,滚动组分缺失或很少.潮流砂(DU1)的平均粒径与分选系数呈良好的正相关,反映潮流的淘洗作用越强,沉积物粒径越粗、分选越好.     

Evidence of rainfall variations in Southern Brazil from trace element ratios (Mg/Ca and Sr/Ca) in a Late Pleistocene stalagmite

Trace element ratios in the Bt2 stalagmite from Botuverá cave, Southern Brazil, are explored as a proxy for changes in the local rainfall recharge during the last 116 ky. BP Mg/Ca and Sr/Ca ratios, measured with an electron microprobe, are significantly positively correlated with one another throughout the entire record, and vary in a way that is very consistent with variations of δ¹⁸O in the same speleothem during the last glacial period. We suggest that prior calcite precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of Mg and Sr into calcite of the stalagmite. This interpretation is supported by trace element correlation patterns and by results from a hydrochemistry study performed in a cave located in the same region and in a similar environmental setting. Therefore, we conclude that higher (lower) Mg/Ca and Sr/Ca values are associated with lower (higher) levels of recharge into the karstic aquifer, as such conditions lead to an increase (decrease) in the volume of calcite precipitated in the unsaturated zone above the cave during dry (wet) climate periods.Trace element variations point to generally dryer (wetter) conditions during lower (high) phases of summer insolation in the southern hemisphere. These periods coincide with decreased (increased) activity of the South American summer monsoon, as revealed by δ¹⁸O stalagmite records. In addition trace element variations show that rather wet conditions persisted throughout most of the last glacial period from approximately 70 to 17 ky BP. We suggest that during this period the glacial boundary conditions, especially ice volume buildup in the northern hemisphere, played an important role for monsoon rainfall intensification in the region.