排序方式： 共有4条查询结果，搜索用时 15 毫秒
1
1.
通过对日本海Ulleung盆地KCES-1孔元素地球化学分析,探讨了过去48 ka以来日本海古生产力和古氧化还原环境的变化规律和影响因素。多种替代指标质量累积速率(总有机碳、CaCO3,磷、过剩钡、镉含量)显示日本海古生产力自48 ka以来发生了显著的变化。在48~18 ka低海平面和有限的水体交换导致表层水古生产力相对较低。在18~11 ka随着海平面的上升,富营养盐水团(亲潮和东海沿岸流水团)的流入导致古生产力逐渐增大,在12.6~11.5 ka古生产力达到最大值。在全新世对马暖流成为影响古生产力变化的重要因素,并且自5 ka以来古生产力保持相对稳定。古氧化还原替代指标(总有机碳、钼、铀、锰、碳与硫含量之比、自生铀、自生钼含量)显示在12~9 ka日本海底层水可能为无氧环境。古生产力高和底层水体有限的交换是诱发底层水缺氧的主要因素,而这又与全球气候变化和海平面变化有关。 相似文献
2.
Rubidium‐strontium and strontium isotope data for eight whole‐rock samples of granite varieties from the Encounter Bay area, South Australia, yield an isochron age of 487 ± 37 m.y. Two specimens of albitised granite, formed as a result of late‐stage metasomatic alteration of original megacrystic granite, conform to this isochron. These data support a genetic relation between granites and late‐stage metasomatic alteration as suspected from field, petrographical and geochemical studies. Eight samples from contiguous Kanmantoo Group metasedimentary rocks have an isochron age of 487 ± 60 m.y. Thus this metamorphic event is coincident with emplacement of the Encounter Bay Granite. The initial Sr87Sr86 ratio for the Encounter Bay Granite (0.719) is significantly higher than initial ratios for the Palmer (0.709) and Anabama (0.705) Granites from the same region and can be attributed to either remobilisation or incorporation of strontium from older crustal material in the intrusion. The apparent initial Sr87/Sr86 ratio for the Kanmantoo Group metasedimentary rocks (0.722) can not be distinguished from that for the Encounter Bay Granite within the analytical uncertainties. Compatability of ages and high initial Sr87Sr86 ratios suggest that the granites formed by remobilisation of associated crustal rock. 相似文献
3.
Since the Xiagou Formation was confirmed to be the primary source rock of the crude oil discovered in the Yumen oilfield, geologists have performed many studies on the sedimentology of the formation, source rock evaluation and migration, as well as petroleum accumulation. In this study, the carbonate-bearing mudstones were investigated using synthetic organic and inorganic geochemical analyses to reconstruct the paleo-environment and study the origin of organic matter during deposition in correlation with organic matter enrichment. The analysed samples have total organic carbon (TOC) and S1 + S2 values in the range of 0.20–3.39 wt% and 0.07–19.50%, respectively, which indicate fair to good hydrocarbon potential. Biomarker studies on the pyrolysis data of the samples suggest that the predominant origin of the organic matter is terrigenous high plants with partial aquatic algae and micro-organisms, primarily oil- and gas-prone. The trace elements P and Ba are considered to be the main proxies for paleoproductivity, and values for the two elements hosted in samples range from 48 to 1724 ppm (a mean of 658 ppm) and from 322 to 1701 ppm (a mean of 550.34 ppm), respectively, which indicates that the sediments in the Xiagou Formation have high paleoproductivity. Additionally, organic geochemical studies reveal that the sediments were deposited in a lacustrine environment with brackish water (low C31-22R-homohopane/C30-hopane ratios; moderate gammacerane and β-carotane), which is consistent with the medium degree of the Sr/Ba ratio, which ranges from 0.22 to 1.42 (a mean of 0.64). Furthermore, the wide range of Cu/Zn and Rb contents are important indicators of a suboxic to relatively anoxic paleoredox condition. This outcome is consistent with the biomarker parameter Pr/Ph, which ranges from 0.05 to 1.37. Moreover, the major oxides and trace elements [high Fe/Mn, low Mg/Ca, low CIA and the plot of SiO2 vs (Al2O3 + K2O + Na2O)] also indicate that the sedimentary paleoclimate was semiarid to arid. Lack of correlation between TOC content and paleo-environment (suboxic, brackish and semiarid) or productivity indicators indicates that the accumulation of organic matter was controlled by combined action, rather than a single factor, such as redox condition or productivity. 相似文献
4.
鱼骨状方解石是一种特殊的碳酸盐沉积,由锯齿状亮暗交互的亚毫米级条带组成,主要见于太古宙。以往认为,鱼骨状方解石属无机化学沉淀成因,形成于水体缺氧、碳酸盐过饱和、富Fe2+、Mn2+等碳酸盐沉淀抑制剂的环境条件;在地质记录中其丰度随时间的减少反映了海洋的长期氧化趋势。文中首次在华北地台中元古界高于庄组四段微生物礁内发现了大量鱼骨状方解石。宏观观察表明,这些鱼骨状方解石主要以微生物礁孔洞充填物形式产出,明显区别于太古宙以海底沉淀形式直接产出在海底的鱼骨状方解石。显微研究发现,鱼骨状方解石晶体纤维具有沿晶体生长方向旋转消光特征,证明其内部亚晶的光学C轴从纤维底部的随机排列逐步旋转至上部垂直纤维生长方向。这符合球状晶体生长模式,需要方解石沉淀抑制剂的参与。鱼骨状方解石产出具有丰度随时间减少以及产出形式由海底沉淀向孔洞胶结物转变的特征。这些特征与海洋氧化逐渐增强以及具氧化还原敏感属性的碳酸盐沉淀抑制剂逐渐从水体中移除相吻合。笔者认为鱼骨状方解石的沉淀抑制剂为Fe2+和Mn2+,这与微生物岩无明显Ce异常和Fe2+极强的抑制能力相一致。因此,鱼骨状方解石可用于指示缺氧环境条件。此外,显微和超微研究也表明鱼骨状方解石晶体内存在有大量与其生长方向一致的菌丝体残余和与之密切伴生的有机矿物,表明微生物为鱼骨状方解石成核和初始沉淀提供了重要垫板。 相似文献
1