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61.
ZHAO Quanhong WANG PinXian CHENG Xinrong Wang Jiliang Huang Baoqi XU Jian ZHOU Zhen JIAN Zhimin 《中国科学D辑(英文版)》2001,44(10):943-951
High-resolution δ13C records are presented for the Miocene benthic foraminifersCibicidoides wuellerstorfi andC. kullenbergi (24-5 Ma) and the planktonic foraminiferGlobigerinoides sacculifer (18-5 Ma) from ODP Site 1148A (18° 50.17’N, 116° 33.93’E, water depth 3308.3 m), northern South China Sea. The general pattern of parallel benthic and planktonic δ13C shows a decrease trend of δ13C values from the early-middle Miocene to the middle-late Miocene. Two distinct δ13C positive excursions at 23.1-22.2 and 17.3-13.6 Ma, and two negative excursions at 10.2-9.4 and 6.9-6.2 Ma have been recognized. All these events are cosmopolitan, providing the good data for the stratigraphic correlation of the South China Sea with the global oceans as well as for studying the changes of the global carbon reservoir and its corresponding climate. 相似文献
62.
A 33 Ma lithostratigraphic record of tectonic and paleoceanographic evolution of the South China Sea
Qianyu Li Pinxian Wang Quanhong Zhao Lei Shao Guangfa Zhong Jun Tian Xinrong Cheng Zhimin Jian Xin Su 《Marine Geology》2006,230(3-4):217-235
The 853 m thick sediment sequence recovered at ODP Site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the South China Sea over the past 33 Ma. Litho-, bio-, and chemo-stratigraphic studies helped identify six periods of changes marking the major steps of the South China Sea geohistory. Rapid deposition with sedimentation rates of 60 m/Ma or more characterized the early Oligocene rifting. Several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 Ma late Oligocene record, providing solid evidence of tectonic transition from rifting/slow spreading to rapid spreading in the South China Sea. Slow sedimentation of 20–30 m/Ma signifies stable seafloor spreading in the early Miocene. Dissolution may have affected the completeness of Miocene–Pleistocene succession with short-term hiatuses beyond current biostratigraphical resolution. Five major dissolution events, D-1 to D-5, characterize the stepwise development of deep water masses in close association to post-Oligocene South China Sea basin transformation. The concurrence of local and global dissolution events in the Miocene and Pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas. A return of high sedimentation rate of 60 m/Ma to the late Pliocene and Pleistocene South China Sea was caused by intensified down-slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low-stands. The six paleoceanographic stages, respectively corresponding to rifting (33–28.5 Ma), changing spreading southward (28.5–23 Ma), stable spreading to end of spreading (23–15 Ma), post-spreading balance (15–9 Ma), further modification and monsoon influence (9–5 Ma), and glacial prevalence (5–0 Ma), had transformed the South China Sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi-enclosed marginal sea in the past 33 Ma. 相似文献
63.
Mitchell J Malone Jonathan B Martin Ulysses S Ninnemann Timothy S White 《Earth and Planetary Science Letters》2004,222(1):275-283
We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ18Osw from the pore water δ18O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ18Osw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ18Osw of 1.0-1.1‰.Using the calculated bottom-water δ18Osw, we have extracted the temperature component from the benthic foraminiferal δ18O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern. 相似文献
64.
白垩纪典型的"温室"气候和海洋一直是地学界关注的焦点之一.与现今地球"冰室"状态相比,温室状态下的气候和海洋遵循着不同的运行模式.本文在近年来取得的大量同位素、古生物以及气候和海洋模拟实验数据的基础上,评述了白垩纪古气候和古海洋研究中取得的重要进展.化石氧同位素数据揭示白垩纪全球平均气温比现今高3～10℃,海洋纬向温度梯度仅0.15～0.3℃/1°,全球海洋结构和大洋环流可能与现今完全不同,大洋环流的驱动很可能是盐度变化而不是温度差异.白垩纪深水沉积显示出从早白垩世碳酸盐台地相、含黑色页岩夹层、黑色页岩和大洋红层大规模出现一直到晚白垩世整体以大洋红层为主的转变.对该沉积转变机制及其与古海洋、古气候关系的研究正是IGCP463/494的主要科学目标. 相似文献
65.
CHEN Lan ZHONG Hong HU Ruizhong XIAO Jiafei TSAI Louis Loung-Yie LIN Andrew Tien-Shun ZOU Yanrong 《《地质学报》英文版》2012,86(5):1143-1153
The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province (China). All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 (C 23 for sample Gzh00-1). The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values (<0.7) suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise. 相似文献
66.
Weiguo Wang Mengwei Zhao Yanguang Liu Min Jiang Chengqiang Wu Yang Liu 《海洋学报(英文版)》2021,40(10):106-117
The grain size distribution of bulk sediment samples was decomposed in a core to reconstruct paleoceanographic evolution over the past 60 ka in the northern Norwegian Sea. The results show that sediments consisted of 3–4 grain populations derived from the North Atlantic Current (NAC) and Barents Ice Sheet (BIS). The grain size data suggest three palaeoceanographic evolution stages: (1) an environment affected by BIS and NAC and changed with the interstadial/stadial transition in phase with the Greenland ice-core record at 60–31 ka BP, during which discharge of icebergs and the content of the coarsest population containing ice-rafted debris (IRD) in the sediments increased significantly during stadial, while the fine silt population containing volcanic glasses increased with the enhancement of NAC during the interstadial; (2) an extreme environment controlled by BIS at 31–13 ka BP. BIS reached to its maximum at about 31 ka BP and the turbid plumes that formed at the leading edge of BIS contributed to a significant increase in the clayey population in sediments. Icebergs drained into the northern Norwegian Sea with periodical calving of the BIS at 31–19 ka BP. Subsequently, the ablation of the BIS discharged massive floods with clayey sediments and icebergs into the Norwegian Sea at 19–13 ka BP, resulting in a constant increase in clay and IRD in sediments; and (3) a marine environment similar to the present one under the strong influence of NAC following the complete melting of the BIS after 13 ka BP, NAC is the dominant transport agent and no IRD occurred in sediments. The fine silt populations containing volcanic glasses transported by NAC significantly increased. 相似文献
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68.
深海沉积重晶石在古海洋研究中的应用 总被引：2，自引：0，他引：2
深海沉积成因重晶石作为重要的古海洋环境指示物,被广泛应用于新生代海洋化学和古生产力的重建,成为全球变化研究的重要分析对象之一。近年来,在重构古海洋生产力和古海水锶含量、锶同位素组成等方面的研究中取得了显著的进展。从目前该领域的研究实践来看,利用深海沉积重晶石进行古海洋研究还需要针对性地解决两方面问题:①形成重晶石沉淀的海洋微环境的时空分布及其物理化学条件;②深海沉积重晶石的采样、筛选和分析方法。上述问题是当前研究的难点,也是制约重晶石广泛用于古海洋研究的基本问题。 相似文献
69.
海陆交互作用下的南黄海沉积环境复杂,其沉积机制一直是古海洋研究的重点和难点。本文以取自南黄海中部泥质区的Z1岩心为载体,对196个样品的粒度和整体有机质指标(TOC、TN、TOC/TN和δ13Corg)进行了详细分析,并对5个层位进行AMS14C年龄测定,分辨率高达11 a/cm。研究结果显示,6.1 ka BP以来南黄海中部沉积过程可分为3个阶段:(1) 6.1～5.2 ka BP,沉积物粒度较粗,以残留砂和陆源粗粒物质为主,有机质含量较低且主要为陆源输入,本阶段多受东亚季风强盛的影响,动荡海洋环境下有机质保存效率低,大量陆源输入冲淡作用显著;(2) 5.2～3.9 ka BP,沉积物粒度变细且波动较大,有机质呈增加趋势且以海源为主,主要受东亚冬季风减弱的影响,海源有机质含量增加,与黄海暖流影响增强有关;(3) 3.9～0 ka BP,沉积物粒度最细且相对稳定,有机质含量继续增加,直至1.9 ka BP趋于稳定,主要受现代环流系统和东亚冬季风影响。结果表明,南黄海粒度和整体有机质指标变化过程复杂,显示中全新世以来南黄海中部泥质区沉积环境演化的复杂性。本研究获得了南黄海高分辨率的沉积环境演化记录,不仅为沉积机制研究提供更多数据支撑,还可为区域古气候和古海洋演化提供关键的指示证据。 相似文献
70.
对我国第五次北极科考在北欧海所采集的两根岩芯样品进行了冰筏碎屑(Ice-Rafted Debris,IRD)丰度、AMS 14C测年、有孔虫丰度统计、浮游有孔虫Neogloboquadrina pachyderma(sin.)(Nps)稳定氧碳同位素及其Mg/Ca重建的次表层海水古温度等指标分析,建立了20ka以来的年代框架。结果表明,在末次盛冰期(20.0~17.5kaBP),次表层温度整体较低(~3℃),钙质生产力下降,冰筏碎屑输入增加;在冰消期(17.5~11.7kaBP)的Heinrich Stadial 1(HS1)事件中较轻的δ^18O和δ^13C指示大量淡水输入,水体分层加剧,向北输送的北大西洋水聚集在次表层,导致次表层水温逐渐升高。从B?lling-Aller?d(B/A)事件开始,次表层水温度达到4.5℃,表明北大西洋水流入增强。早全新世(11.7~8.2kaBP)早期次表层温度达到6.5℃,钙质生产力升高,冰筏碎屑输入降低;在中全新世(8.2~4.2kaBP)早期(8.2~5.6kaBP),钙质生产力逐渐升高反映通风作用增强,导致营养盐供应增加;6.6~5.6kaBP,明显降低的次表层温度(~4℃)反映夏季太阳辐射量降低以及大西洋水流入减弱;5.6~4.2kaBP期间次表层水变暖导致δ^18O偏轻,而δ^13C轻值反映生产力降低。晚全新世(4.2~0.8kaBP)的新冰期(4.2~3.0kaBP),次表层温度逐渐降低,Nps-δ^13C偏轻反映生产力下降,Nps-δ^18O偏轻以及IRD增加反映冰融水排放。3.0kaBP以来,生产力上升,次表层水体温度不断上升,可能是向北输送的北大西洋水增强。 相似文献