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391.
J Jouzel R Vaikmae J R Petit M Martin Y Duclos M Stievenard C Lorius M Toots M A Mélières L H Burckle N I Barkov V M Kotlyakov 《Climate Dynamics》1995,11(3):151-161
The two-step character of the last deglaciation is well recognized in Western Europe, in Greenland and in the North Atlantic. For example, in Greenland, a gradual temperature decrease started at the Bölling (B) around 14.5 ky BP, spanned through the Alleröd (A) and was followed by the cold Younger Dryas (YD) event which terminated abruptly around 11.5 ky BP. Recent results suggest that this BA/YD sequence may have extended throughout all the Northern Hemisphere but the evidence of a late transition cooling is still poor for the Southern Hemisphere. Here we present a detailed isotopic record analyzed in a new ice core drilled at Dome B in East Antarctica that fully demonstrates the existence of an Antarctic cold reversal (ACR). These results suggest that the two-step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences. Thus, the coldest part of the ACR, which shows a temperature drop about three times weaker than that recorded during the YD in Greenland, may have preceded the YD. Antarctica did not experienced abrupt changes and the two warming periods started there before they started in Greenland. The links between Southern and Northern Hemisphere climates throughout this period are discussed in the light of additional information derived from the Antarctic dust record. 相似文献
392.
Jiamo Fu Guoying Sheng Deyu Chen Dehan Liu S. C. Brassell A. Gowar G. Eglinton 《中国地球化学学报》1987,6(4):289-296
A preliminary study of newly discovered sphagnum brown coal from the Jingsuo Basin, Yunnan Province, China, which is quite
rich in montan wax, indicates the predominance of highern-alkane homologues and aromatized triterpenoid components. Aromatic hydrocarbons are composed mainly of pentacyclic and tetracyclic
di-, tri- and tetra-aromatic components, which are obviously diagenetically related to higher plant-derived triterpenoids
naturally occurring in the biosphere. Because the sphagnum brown coal still remains in the highly immature stage, it seems
that the progressive diagenetic aromatization of the higher plant-derived triterpenoids may start at a very early stage. 相似文献
393.
Sulphur-containing compounds in sulphur-rich crude oils from hypersaline lake sediments and their geochemical implications 总被引:1,自引:0,他引:1
Guoying Sheng Jiamo Fu S. C. Brassell A. P. Gowar G. Eglinton Jaap S. Sinninghe Damste Jan W. de Leeuw P. A. Schenck 《中国地球化学学报》1987,6(2):115-126
Three sulphur-rich commercial crude oils have been studied, which contain sulphur as high as up to 4–12%. These samples were
collected from Tertiary hypersaline lake sediments of the Jianghan Basin, Hubei Province at different depths, but above the
oil generation threshold (2200m). FPD-GC and GC-MS data show that aromatic fractions of the crude oils are composed of different
homologues of sulphur-containing compounds, including long-chain normal alkyl-thiophenes and-thiolanes, long-chain isoprenoid-thiophenes
and -thiolanes, and benzothiophenes. It is worth noting that the distribution patterns of long-chain alkyl-thiophenes and
-thiolanes from two shallow-seated crude oils are quite similar to those of normal alkanes showing marked even-odd predominance.
It seems that the even-odd predominance of sulphur-containing compounds decreases with increasing burial depth of the crude
oils. The major component of aliphatic fraction is phytane, and similarly the major peaks of aromatic fractions also represent
C20 isoprenoid thiophenes.
Some preliminary conclusions have been drawn from the above discussion: (1) Abundant sulphur-containing compounds may be used
as an indicator of low mature or immature crude oils produced from hypersaline lake sediments; (2) Sulphur-containing compounds
are considered to be early diagenetic products of reactions between elemental sulphur or sulfides and alkanes or their precursors
(phytols, fatty acids, alcohols, etc.), or of bacterial activities, but not direct inputs of organisms. 相似文献
394.
分布在五台山区的早前寒武纪五台群和滹沱群,遭受了多期变形和变质,小型构造发育。层理配置反映变形性质和程度;片理(劈理)为早世代挤压-剪切褶皱的轴面片理,又成为晚世代弯滑褶皱的滑动面;线理(压扁拉长的砾石、杏仁体和矿物集合体)垂直于早世代褶皱枢纽,为a线理;这一运动学特征在显微组构中亦有反映。本区发现了“折射变位”、“非共面反射变位”和“共面反射变位”等褶皱枢纽变位轨迹。上述构造形迹可为运动学分析提供依据,可对造山带的重要性质获得广泛的理解。 相似文献
395.
396.
包气带土体生物地球化学特征与氮转化研究—以河北平原正定试验场剖面为例 总被引:7,自引:1,他引:6
为研究氮素的生物地球化学循环问题,通过对河北平原典型试验场贯穿包气带18.5m钻孔剖面土样的物理性质,地球化学指标,有机质含量的测试和微生物的培养鉴定,发现土体的氮素,可溶盐含量(TDS),Cl^-含量以及微生物细菌的变化随深度不呈简单的线性分布。经分析认为,剖面中的粘性土层是生物的活性层,在氮素转化过程中起主导作用;剖面中多种指标的变化与地质结构呈良好 对应关系,反映环境演化的过程,同时表明,包气带存在着更多尚待提取的全球变化对比研究信息。 相似文献
397.
398.
根据苏北地区大地电磁勘探环境特点进行了电极距长度、磁场位置和采集时长的试验工作,确定了大地电磁测深勘探技术参数设置下限,电极距长度不能小于50m,采集时间要大于8h,磁距应控制在2km范围内。 相似文献
399.
分析了2004年7月10日北京城区暴雨、灾情及其成因,提出了既能缓解城市短历时暴雨灾情、又能充分利用城市雨水的减灾措施。 相似文献
400.
通过对不同温度、盐分和干旱胁迫对刚毛柽柳种子萌发实验研究影响,结果表明:刚毛柽柳种子的适宜萌发温度范围为10~35℃,萌发率高达80%以上,且萌发迅速。不同浓度NaCl溶液对刚毛柽柳种子萌发有明显抑制作用,种子萌发率随NaCl溶液浓度的增大而下降,到0.7 mol/L时,萌发率仅为1.67%,种子发芽受到抑制。相同渗透势PEG-6 000溶液中的萌发率低于NaCl溶液,渗透势为-0.5 MPa是二者影响作用的分界点。渗透势为-1.8 MPa时,萌发率已急剧下降到0,其对种子萌发的抑制作用大于NaCl溶液。将在两溶液中处理10天的种子转移至蒸馏水后,随着NaCl溶液浓度的增大,萌发恢复率逐渐升高,0.7 mol/L时,萌发恢复率为60%;随着PEG-6 000溶液浓度增大,萌发恢复率先升高后降低,渗透势为-1.4 MPa时,种子萌发恢复率达到最大为67.5%,但两种处理下种子的最终萌发率(总萌发率)都低于在蒸馏水中的。 相似文献