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101.
冷泉区底栖有孔虫研究进展 总被引:1,自引:0,他引:1
海底冷泉区是海洋能源和生物资源同时富集的一类特殊区域。底栖有孔虫群落及其地球化学组成是海底冷泉区发育的重要指示标志之一。海底冷泉区的底栖有孔虫及其碳同位素研究,对于探讨冷泉演化、评估古冷泉甲烷排放对全球气候变化的影响有重要的研究意义。综述了全球一些主要冷泉区的底栖有孔虫研究方法及其进展,对比了各冷泉区底栖有孔虫群落结构的主要特征及地域差异,评述了冷泉区底栖有孔虫的碳同位素记录特征、影响因素及其对冷泉活动的潜在指示意义,最后提出了南海北部冷泉活动区底栖有孔虫方面的研究展望。 相似文献
102.
壳体大小对浮游有孔虫生物地球化学记录的影响 总被引:1,自引:0,他引:1
徐建 《矿物岩石地球化学通报》2010,29(2):109-118
在浮游有孔虫壳体稳定同位素及Mg/Ca和Sr/Ca值的相关研究中,人们常因各种原因而选择不同粒径的壳体进行分析测试,而很少注意壳体大小可能导致研究结果的分歧。针对这一问题,本文分析了位于低纬度海区钻孔中不同粒径的Glo-bigerinoides ruber(白色,sensu stricto)和Pulleniatinaobliquiloculata壳体,结果表明G.ruber壳体的δ13C值受壳体大小的影响最为强烈,表现为正相关关系,不同粒径壳体的δ13C绝对平均差值可达0.48‰±0.12‰和0.25‰±0.09‰;P.obliquiloc-ulata400μm与315~400μm和250~315μm壳体Mg/Ca值的差异相当于1.8℃的海水温度;相对而言,G.ruberδ18O和Mg/Ca值以及P.obliquiloculataδ13C受壳体大小的影响较小,但它们的Sr/Ca值与壳体大小的关系不显著。本文推测,壳体大小相同时厚重的壳体可能成壳速度较快,相对优先吸收轻的同位素,且壳体Mg/Ca值可能更接近周围海水的水平。据此,本文认为较大个体P.obliquiloculata的壳体分泌可能与周围海水达到了平衡分馏。 相似文献
103.
Holocene paleoenvironmental changes have been interpreted on the basis of benthic foraminifera and calcareous nannofossils recovered in samples from Napostá Grande Stream, Bahía Blanca estuary, southern Buenos Aires Province. Samples are fine sands and clay sediments from a Holocene outcrop and were studied with quantitative techniques. The benthic foraminiferal assemblage is dominated by Ammonia parkinsoniana, Ammonia tepida, Bolivina pseudoplicata, Bolivina striatula, Bolivina sp., Buccella peruviana, and Elphidium spp. The calcareous nannofossil assemblage recovered is a typical cold-water association, dominated by Calcidiscus leptoporus, Coccolithus pelagicus, Emiliana huxleyi and Gephyrocapsa oceanica. A dendrogram classification by cluster analysis was made for each microfossil group. The results of these analyses were coincident, showing a liaison between changes in the assemblages of benthic foraminifera and calcareous nannofossils. Those results, jointly with the sedimentological information, lead to the identification of three different paleoenvironments along the Napostá N1 site. The lower part of the succession represents an estuarine environment with larger marine connection. The middle part represents a gradual passage to a more restricted estuarine environment, and the upper part represents the establishment of the modern continental fresh-water environment. 相似文献
104.
Manish Tiwari Rengaswamy Ramesh Ravi Bhushan Madavalm S. Sheshshayee Bammidipati L. K. Somayajulu A. J. Timothy Jull George S. Burr 《第四纪科学杂志》2010,25(7):1179-1188
A few studies from the western Arabian Sea indicate that the Indian summer (or southwest) monsoon (ISM), after attaining its maximum intensity at ca. 9 ka, declined during the Holocene, as did insolation. In contrast, earlier and later observations from both the eastern and the western Arabian Sea do not support this inference. Analysis of multiple proxies of productivity in a new sediment core from the western Arabian Sea fails to confirm the earlier, single‐proxy (e.g. abundance of Globigerina bulloides) based, inference of the Holocene weakening of ISM, following insolation. The reason for the observed decreasing trend in foraminiferal abundance – the basis for the earlier inference – could be the favouring of silicate rather than carbonate productivity by the increased ISM wind strength. Although ISM exhibits several multi‐millennial scale fluctuations, there is no evidence from several multi‐proxy data to conclude that it declined during the Holocene; this is consistent with the phase lag analysis of longer time series of monsoon proxies. Thus, on sub‐Milankovitch timescales, ISM did not follow insolation, highlighting the importance of internal feedbacks. A comparison with East Asian summer monsoon (EASM) records suggests that both ISM and EASM varied in unison, implying common forcing factors on such longer timescales. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
105.
ZHAO Quanhong JIAN Zhimin Wang Jiliang CHENG×inrong Huang Baoqi XU Jian ZHOU Zhen FANG Dianyong WANG Pin×ian 《中国科学D辑(英文版)》2001,44(10):934-942
A detailed stable isotopic study based on benthic foraminifera from 1165 samples of ODP Site 1148 (18° 50.17.3’N, 116° 33.93’E,
water depth 3308.3 m), northern South China Sea, provides an excellent oxygen isotopic record with an average resolution of
30 ka. It contains the most continuous δ18O data with highest resolution for the whole Neogene sequence in the world. The δ18O curve shows a step-like increasing upwards and records 5 increases, 3 decreases and 2 stable stages during the Neogene,
reflecting the general trend of global cooling. Among these events the δ18O decrease at 17.2–14.5 Ma, and two δ18O increases at 14.5-13.6 and 3.0-2.4 Ma are most marked and globally comparable. The intervals at 13.6-10.2 and 6.0-3.0 Ma
with the lowest-amplitude and least fluctuation in δ18O represent the most stable bottom water periods for the South China Sea. 相似文献
106.
Qian JianxingThe Second Institute of Oceanography SO A Hangzhuu Zhejiang Liu Linqun 《《地质学报》英文版》1995,69(2)
Based on a comparison between the oxygen isotope records of benthic and plank tonic foraminifers from core 8KL of the South China Sea and sea-level change records derived from the Huon Peninsula, New Guinea, it is found that both records are very similar from 72 K a B.P. to the present, especially for the benthic oxygen isotope record. The linear regression shows that δ18O changes (0.9995‰ for benthic foraminifers and 1.022‰ for planktonic foraminifers) are equal to 100 m in sea-level fluctuation. After making temperature correction in the δ18O record of benthic foraminifers from 72 to 120 Ka B.P., the curve of sea-level oscillation of the South China Sea since 186 Ka B.P. has been reconstructed. The lowermost sea - level that occurred in the last glacial maximum and oxygen isotope stage 6 is approximately - 130 m. 相似文献
107.
108.
渤海湾牡蛎礁平原中部兴坨剖面全新世地质环境变迁 总被引:9,自引:8,他引:9
渤海湾牡蛎礁平原中部兴坨剖面的有孔虫组合划分为5种沉积环境7个带(亚环境),从下向上依次为晚更新世陆相(Ⅶ带)、早全新世海陆过渡相(Ⅵ带:沿海低地与潮间带)、中晚全新世海相(Ⅴ带:潮下带-浅海,Ⅳ带:低潮线附近)、晚全新世海陆过渡相(Ⅲ带:开放潮间带,Ⅱ带:渴湖)和河流泛滥相(Ⅰ带:古土壤及洪积层)。^14C确定了全新世底泥炭始于9486 cal BP,Ⅳ带始于约4696 cal BP。Ⅱ带所处的渴湖环境,从约4000 cal BP直至隋唐温暖期之前,历时约2700年。隋唐暖期古土壤发育向南东减弱至逐渐消失,说明在比兴坨更靠近渤海湾的地方,潟湖持续的时间更长。广泛存在的潟湖,是牡蛎礁平原晚全新世的重要地貌景观。 相似文献
109.
Marie Alexandrine Sicre Laurent Labeyrie Ullah Ezat Josette Duprat Jean Louis Turon Sabine Schmidt Elisabeth Michel Alain Mazaud 《Earth and Planetary Science Letters》2005,240(3-4):724-731
The lack of temporal resolution and accurate chronology of Southern Ocean marine cores has hampered comparison of glacial millennial-scale oscillations between the Southern Ocean, Antarctic ice and other records from both hemispheres. In this study, glacial climate variability is investigated over the last 50 ka using a multi-proxy approach. A precise chrono-stratigraphy was developed on the high-sedimentation rate core MD94-103 (Indian Southern Ocean, 45°35′S 86°31′E, 3560 m water depth) by geomagnetic synchronization between the later core and NAPIS75, and 14C dates. High-resolution time-series of δ18O in planktonic foraminifera Globigerina bulloides and Neogloboquadrina pachyderma, and sea surface temperatures (SSTs) estimated from the alkenone UK′37 index and foraminifera assemblages have been generated. Temporal evolution of the two temperature proxy records is notably different during the last glacial period. While foraminifera data indicate a consistent cooling towards the last glacial maximum, anomalous warm glacial alkenone temperatures suggest a strong advection of warm “detrital” alkenones by surface waters of the Agulhas current. Superimposed to this general trend, during Heinrich events, foraminiferal SSTs point to warmer surface waters, while concurrent alkenone SSTs exhibit apparent coolings probably caused by enhanced local alkenone production. By analogy to modern observations, possible influence of ENSO-like conditions on the subantarctic Southern Ocean SSTs is discussed. 相似文献
110.
Sediment production and dispersal on foraminifera-dominated early Tertiary ramps: the Eocene El Garia Formation, Tunisia 总被引:4,自引:0,他引:4
Larger benthic foraminifera Nummulites are common within Eocene, circum-Tethyan limestones. Despite their importance as sediment producers, contradictions in the literature constrain current understanding about the location of the Nummulites‘factory’. The El Garia Fm was deposited on a ramp with localized palaeohighs, and whilst some authors suggested that the locus of Nummulites production was in shallow water across the palaeohighs, others concluded that production was significantly reduced over these palaeohighs, and concentrated in the surrounding deeper (30–60 m) water. There are also marked dissimilarities between recent models in terms of the continuity, correlation and resolution of depositional sequences. To assess these models, we integrate studies of the architecture and geometry of the El Garia Fm with detailed taphonomic, biometric, biofabric and palaeoecological characterization of Nummulites tests. We conclude that the highest rates of sediment production occurred in euphotic water over the palaeohighs and in nearshore environments. Nummulites on the palaeohighs were transported into the surrounding deeper water by oceanic and storm currents that swept the platform top, producing a nummulitic sediment package that thickened and became increasingly fine-grained and fragmented into outer ramp environments. This transport exerted a major control on development of the ramp-like geometries often seen at outcrop. Our findings question the validity of a recent sequence stratigraphic model that identifies decimetre-scale Milankovitch cycles, even in largely allochthonous, ‘bio-retextured’, mid/outer ramp sediments. Our findings also suggest that the thin packages of El Garia Fm on the palaeohighs, which have previously been interpreted as condensed sections that can be correlated with thicker, more distal accumulations, actually represent remnants of the sediment that was produced on the highs and ‘exported’ into the basin. 相似文献