Relationship between chemical composition and magnetic susceptibility in sediment cores from Central Indian Ocean Basin

Three sediment cores in a north-south transect (3°N to 13°S) from different sediment types of the Central Indian Ocean Basin (CIOB) are studied to understand the possible relationship between magnetic susceptibility (χ) and Al, Fe, Ti and Mn concentrations. The calcareous ooze core exhibit lowest χ (12.32 × 10⁻⁷ m³ kg⁻¹), Al (2.84%), Fe (1.63%) and Ti (0.14%), terrigenous clay core with moderate χ (29.93 × 10⁻⁷ m³ kg⁻¹) but highest Al (6.84%), Fe (5.20%) and Ti (0.44%), and siliceous ooze core with highest χ (38.06 × 10⁻⁷ m³ kg⁻¹) but moderate Al (4.49%), Fe (2.80%) and Ti (0.19%) contents. The distribution of χ and detrital proxy elements (Al, Fe, and Ti) are identical in both calcareous and siliceous ooze. Interestingly, in terrigenous core, the behaviour of χ is identical to only Ti content but not with Al and Fe suggesting possibility of Al and Fe having a non-detrital source. The occurrence of phillipsite in terrigenous clay is evident by the Al-K scatter plot where trend line intersects K axis at more than 50% of total K suggesting excess K in the form of phillipsite. Therefore, the presence of phillipsite might be responsible for negative correlation between χ and Al (r = −0.52). In siliceous ooze the strong positive correlations among χ, Al_exc and Fe_exc suggest the presence of authigenic Fe-rich smectite. High Mn content (0.5%) probably in the form of manganese micronodules is also contributing to χ in both calcareous and siliceous ooze but not in the terrigenous core where mean Mn content (0.1%) is similar to crustal abundance. Thus, χ systematically records the terrigenous variation in both the biogenic sediments but in terrigenous clay it indirectly suggests the presence of authigenic minerals.     

Systematic biotic responses to palaeoenvironmental change in the Late Pleistocene southern South China Sea: a preliminary study

Oxygen and carbon isotopes from the planktonic foraminifer Globigerinoides sacculifer, trace element contents, calcium carbonate, biogenic silica, grain size, and abundances of diatoms, radiolarians and foraminifera in a deep‐sea core from the southwestern South China Sea were analysed to investigate the response of various marine ecological communities to environmental changes over the last 200 ka. The synthesised results show that the quality of the palaeoecological environment for biological growth is primarily affected by nutrient supply and terrigenous disturbance. Ba and P are important nutrient elements for the growth of diatoms, radiolarians and planktonic foraminifera. Together with dissolved silica and calcium carbonate in sea water, these elements may control microbiotic development. However, variations in Fe content appear to affect diatom and radiolarian abundance. Optimal biotic growth occurs when nutrients are abundant and when there is minimal terrigenous disturbance. Biotic growth decreases when sea water is highly oligotrophic and terrigenous input is high. Maximum biological growth occurred in the mid Holocene, but deteriorated soon afterwards owing to increased terrigenous input, causing a decrease of biological abundance and productivity in the late Holocene. The results also indicate how the Toba volcanic eruption ca. 74 ka ago contributed to changing the ecological environment in the southern South China Sea. Copyright © 2008 John Wiley & Sons, Ltd.     

Late Pleistocene ice export events into the Arctic Ocean from the M'Clure Strait Ice Stream, Canadian Arctic Archipelago

Rapidly-flowing sectors of an ice sheet (ice streams) can play an important role in abrupt climate change through the delivery of icebergs and meltwater and the subsequent disruption of ocean thermohaline circulation (e.g., the North Atlantic's Heinrich events). Recently, several cores have been raised from the Arctic Ocean which document the existence of massive ice export events during the Late Pleistocene and whose provenance has been linked to source regions in the Canadian Arctic Archipelago. In this paper, satellite imagery is used to map glacial geomorphology in the vicinity of Victoria Island, Banks Island and Prince of Wales Island (Canadian Arctic) in order to reconstruct ice flow patterns in the highly complex glacial landscape. A total of 88 discrete flow-sets are mapped and of these, 13 exhibit the characteristic geomorphology of palaeo-ice streams (i.e., parallel patterns of large, highly elongated mega-scale glacial lineations forming a convergent flow pattern with abrupt lateral margins). Previous studies by other workers and cross-cutting relationships indicate that the majority of these ice streams are relatively young and operated during or immediately prior to deglaciation. Our new mapping, however, documents a large (> 700 km long; 110 km wide) and relatively old ice stream imprint centred in M'Clintock Channel and converging into Viscount Melville Sound. A trough mouth fan located on the continental shelf suggests that it extended along M'Clure Strait and was grounded at the shelf edge. The location of the M'Clure Strait Ice Stream exactly matches the source area of 4 (possibly 5) major ice export events recorded in core PS1230 raised from Fram Strait, the major ice exit for the Arctic Ocean. These ice export events occur at 12.9, 15.6, 22 and 29.8 ka (¹⁴C yr BP) and we argue that they record vigorous episodes of activity of the M'Clure Strait Ice Stream. The timing of these events is remarkably similar to the North Atlantic's Heinrich events and we take this as evidence that the M'Clure Strait Ice Stream was also activated around the same time. This may hold important implications for the cause of the North Atlantic's Heinrich events and hints at the possibility of a pan-ice sheet response.     

Neoproterozoic terrigenous deposits of the Tuva–Mongolian massif: geochemical correlation, sourcelands, and geodynamic reconstruction

We have established that the terrigenous deposits of the Haisuin Formation and metamorphic deposits of the Shutkhulai block are similar in geochemical characteristics to the rocks of the Oka Group. The volcanics of the Sarkhoi Group and, to a lesser extent, the crystalline deposits of the Gargan block and rocks of the Dunjugur ophiolite complex served as sourcelands for the studied deposits. The terrigenous deposits of the Oka Group and Haisuin Formation and the pararocks of the Shutkhulai block accumulated in the same sedimentary basin localized on the margin of the Tuva–Mongolian massif in the setting of an island-arc system.     

末次冰消期以来白令海盆的冰筏碎屑事件与古海洋学演变记录

通过对白令海盆中部BR02岩芯高分辨率的颜色、粒度和元素地球化学地层的研究发现:(1)该岩芯较为完整地记录了末次盛冰期结束以来(约16.3 ka BP)的多期冰筏碎屑事件,包括H1、OD、YD和北方2期,其中以H1和YD最为显著,反映了末次冰消期以来该地区海冰/冰山以及区域性冰川的消长变化;(2)BR02岩芯上部17—25 cm段出现富Mn、富Ba的氧化型沉积,说明在全新世高海面时期,白令海与北太平洋、北冰洋之间的水体交换达到极点,白令海环流加强,海盆底层水含氧状况明显改善,并引发海洋生产力增加;(3)CaO、Na2O、Sr、Zr及Na2O/K2O比值的分布说明,海盆冰筏碎屑主要来自富碳酸盐的育空河流域,其次为阿拉斯加半岛和阿留申群岛等火山岩区;岩芯上部Na2O/K2O比值的递增暗示10 ka BP以来与火山物质输运有关的北太平洋入流(阿拉斯加流)可能增加。     

Use of biomarkers indices in a sediment core to evaluate potential pollution sources in a subtropical reservoir in Brazil

The presence of PAHs, n-alkanes, pristane, and phytanes in core sediment from the Vossoroca reservoir (Parana, southern Brazil) was investigated. The total concentration of the 16 PAHs varied from 15.5 to 1646 μg kg⁻¹. Naphthalene was present in all layers (3.34–74.0 μg kg⁻¹). The most abundant and dominant n-alkanes were n-C₁₅ and n-C₃₆, with average concentrations of 198.1 ± 46.8 and 522.9 ± 167.7 μg kg⁻¹, respectively. Lighter n-alkanes were distributed more evenly through the layers and showed less variation, specially n-C₉, n-C₁₂, and n-C₁₈, with average concentrations of 14.6 ± 3.0, 31.6 ± 1.9, and 95.0 ± 5.2 μg kg⁻¹, respectively; heavier n-alkanes were more unevenly distributed.     

南海北部神狐海域现代沉积物正构脂肪酸来源:加权平均碳同位素的建立与应用

对南海北部神狐海域表层沉积物中脂肪酸组分进行了分析,检测到的总正构脂肪酸含量为1.80~10.16μg/g(μg脂肪酸/g干沉积物),碳数分布为C12—C32,呈偶奇优势分布,以C16和C18为主峰碳。将90cm以上层位样品进行归一化,建立加权平均碳同位素讨论正构脂肪酸来源,结果表明,短链脂肪酸(n-C14~18)具有较正的碳同位素组成(加权平均为-26.7‰^-28.2‰),反映了化学自养细菌来源;大部分长链脂肪酸(n-C21~23,nC25,n-C29~32)具有偏负的碳同位素组成(加权平均为-29.6‰^-34.1‰),反映了陆源C3高等植物来源;而另外的长链脂肪酸(n-C24&n-C26~28)和n-C19~20中链脂肪酸(加权平均碳同位素为-26.1‰^-29.3‰)则可能反映了混合来源输入。沉积物75~80cm层位陆源输入和海洋输入含量达到最低,可能和Younger Dryas冷期旋回事件有关。     

陆源碎屑与碳酸盐混积岩及其油气地质意义

根据混积岩的分类命名、沉积环境和沉积模式等的研究现状及其在石油地质领域的研究进展,综合分析得出：有利 于混合沉积的沉积相主要是滨海相、滨浅湖相,其次是浅海陆棚、陆表海、三角洲相等;对其沉积环境的分析表明,滨海 相混积岩发育的控制因素是潮汐作用、相对比较强的水动力条件以及有利于低等生物发育的浅海环境,控制滨浅湖相混积 岩发育的因素是频繁的湖平面和气候的变化;因此认为深入探讨混积岩的沉积微相及其环境因素,对于完善和统一混积岩 独立的分类方案和命名体系是一有效途径。在此基础上,结合柴西北区古近系和新近系中深层湖相混积岩的研究实例,初 步提出了湖相和海相的混合沉积综合模式示意图;根据与混积岩相关的烃源岩和油气储层的研究资料认为,滨、浅海相和 滨、浅湖等海（湖）陆过渡地带的混合沉积,也可成为优质储层和烃源岩的勘探靶区。