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1.
It has been established that important changes in the marine environment and the biosphere occurred during the Cambrian. However, the relationships between the so-called “Cambrian Explosion” and the concomitant environmental changes are not yet fully understood. This study presents new geochemical data from the black shale successions from different facies belts of the Yangtze Platform in South China. Variations in the concentrations of REE and trace elements (varying Ce/Ce*, Th/U, V/Sc, and V/Cr ratios) in kerogen as well as in bulk rocks from different depositional environments along a transect from platform to basin indicate two oxidation events, which led to the oxygenation of the water column in shallow-marine environments and euxinic conditions (weak correlation between TOC, V, U, and Mo) in the deeper sea. During the first oxidation event in the late Terreneuvian, anoxic conditions in bottom waters rapidly changed to euxinic conditions. Subsequently, the second oxidation event during the early Epoch 2 of the Cambrian led to oxic–suboxic conditions in deeper seawater. 相似文献
2.
岩石显微构造分析现代技术——EBSD技术及应用 总被引：10，自引：0，他引：10
EBSD技术的发展，为岩石显微构造分析开辟了一个全新的领域。它与现代扫描电子显微镜和能谱分析等设备配合，可以同时对块状样品进行晶体结构与成分分析,从而使显微构造、微区成分与结晶学数据分析有机结合起来。
EBSD技术可以精确、快速定量标定包括各种晶系晶体颗粒的晶格方位和描述晶体颗粒的边界、形态等特征，对于具有低角度边界的晶体颗粒提供精确数据,为阐述岩石变形机制提供重要约束，并为高级晶族和不透明矿物结晶学组构与变形机制研究提供了有效的手段。EBSD尤其使获取微米级甚至纳米级尺度上颗粒（亚颗粒）或相之间的定向差别（达到20 nm的空间分辨率和0.3度角度分辨率）成为可能。EBSD技术在矿物相鉴定、亚微域内的应变分析、矿物出溶作用等方面的应用，进一步证明了这一新技术在显微构造分析及相关领域的应用前景。其广泛应用必将带来岩石显微构造研究的新突破，也将成为未来岩石变形机制与岩石圈流变学研究取得飞速发展不可或缺的技术手段。 相似文献
3.
Shangyue Shen Qinglai Feng Wenqiang Yang Zhibin Zhang Chongpom Chonglakmani 《中国地球化学学报》2010,29(4):337-342
Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were
analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating
that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is
basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite
series coming next. The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the
enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf.
The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks
in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic
rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed
in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great
significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone. 相似文献
4.
Zhou W. D. Xie S. Y. Bao Z. Y. Carranza E. J. M. Wang Y. Tang M. L. 《Mathematical Geosciences》2022,54(1):131-150
Mathematical Geosciences - Inorganic pore structures are critical to understand the oil and gas transport and storage properties of unconventional reservoirs. However, it can be difficult to... 相似文献
5.
Itaru Yamashita Adichat Surinkum Yutaka Wada Makoto Fujihara Masao Yokoyama Haider Zaman Yo-ichiro Otofuji 《Journal of Asian Earth Sciences》2011,40(3):784-796
Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α95 = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α95 = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin. 相似文献
6.
Xianyu Huang Shucheng Xie Chuanlun L. Zhang Dan Jiao Junhua Huang Jianxin Yu Fang Jin Yansheng Gu 《Organic Geochemistry》2008,39(12):1765
Aliphatic des-A-triterpenoids have been tentatively assigned in samples taken from a 260 cm thick peat sequence from the Dajiuhu Basin of southern China using gas chromatography–mass spectrometry (GC–MS). The compounds, possessing the carbon skeletons of oleanane, ursane or lupane, are generally considered as the microbial degradation products of plant triterpenoids under anoxic conditions. Abundant aliphatic des-A-triterpenoids were observed only in peat samples during the transitional period from the last glaciation to the early Holocene (9.5–11.6 cal 14C ka BP). Among these, des-A-lupane is the only saturated ring A-degraded compound, whilst mono- and di-unsaturated des-A-triterpenes are dominated by oleanane and ursane derivatives. The mono- and di-unsaturated des-A-triterpenes show a strong correlation (R2 0.94) in abundance, indicating that they may be derived from the same source or process. Des-A-lupane shows no correlation in abundance with the mono- or di-unsaturated des-A-triterpenes (R2 < 0.25) and may be derived from a different source or process in the catchment. The period with abundant aliphatic des-A-triterpenoids corresponds to the interval with relatively high sedimentation rate (> 0.3 mm per year). These data indicate that the abundance of aliphatic des-A-triterpenoids in the Dajiuhu peat deposit in the early Holocene may result from the prevailing reducing conditions in the water table or surficial sediment and/or rapid preservation of the early diagenetic products. Our study highlights the potential application of des-A-triterpenes in the reconstruction of palaeoenvironments based on peat sequences. 相似文献
7.
This study was undertaken in the south and western regions of the Amazonas Basin to describe the conodont biostratigraphy and paleoecology of Pennsylvanian carbonate rocks of the marine portion of the Tapajós Group comprising the upper Monte Alegre, Itaituba, and lower Nova Olinda formations.The analyzed area includes one outcrop along the Tapajós river (TAP), two carbonate quarries (QI, QII), and 18 wells (dots 1–18). The conodont fauna is dominated by Idiognathoides sinuatus and Neognathodus symmetricus in the Monte Alegre Formation, followed by Idiognathodus incurvus, Diplognathodus coloradoensis and Neognathodus bassleri in the Itaituba and Nova Olinda formations. The conodont association suggests an Early to Middle Pennsylvanian age to the analyzed section. Relative ages attributed to the three lithostratigraphic units using conodonts, palynomorphs, and foraminifers are consistent.Herein are proposed one local taxon-range zone of Idiognathodus incurvus in the Itaituba and lower part of the Nova Olinda Formation and one local taxon-range subzone of Diplognathodus coloradoensis in the Itaituba Formation, suggesting a late Bashkirian – Moscovian (Atokan – early Desmoinesian) age to these strata.The Itaituba Formation marks the establishment of large Pennsylvanian marine conditions in the Amazonas Basin and is composed primarily of marine carbonates of abundant fossil content, tidal flat evaporites and siliciclastic thin intervals. Its lower limit, with the Monte Alegre Formation, is characterized by the predominant occurrence of fluvial-deltaic sandstones superimposed on an extensive sequence of aeolian sandstones, siltstones and shales intercalated with the interdune and lakes. From the upper strata of Itaituba Formation the faunal and lithological characteristics indicate the occurrence of a regressive phase culminating in a restricted environment, arid which indicates the Nova Olinda Formation. This is characterized by the occurrence of evaporites increasingly abundant to the top of carbonates, also shales and siltstones intercalated with the sabkha plain. The carbonate strata have similar marine fossils to those of Itaituba Formation, however, the fauna becomes impoverished in abundance and diversity. The conodont fauna of Early-Middle Pennsylvanian of Amazonas Basin suggests similarities of species with the North American Midcontinent region and the Illinois Basin indicating their probable cosmopolitism; however in a slightly different paleogeographic context, probably due to latitudinal differences, coal deposits are present in North America, whereas widespread evaporitic deposits are registered to the Tapajós Group, Amazonas Basin. 相似文献
8.
分子地层学的原理、方法及应用实例 总被引：2，自引：1，他引：2
当前分子地层学研究已涉及蛋白质、核酸、碳水化合物、类脂物和木质素等多种生物化学组分。在地层中,分子化石具有分布的广泛性、定量的准确性、应用的指纹性和信息的多样性等特点,其地层学应用的主要原理是依据分子化石的生物源信息和其离开生物体后发生的一系列转化途径来实现的,其表述方法可以是含量、相对丰度、碳数分布和单体同位素特征等。在各类年代学框架下,由这些分子化石参数所揭示的各类生物事件和环境事件可以成为区域性乃至全球性地层对比的主要依据。分子地层学与分子古生物学、生物地球化学、有机地球化学密切相关,它与传统三大地层学分支学科明显不同,目前还没有明确的分子地层单位,也没有进行广泛的分子地层划分与对比工作。对各类生物事件与环境事件有重要指示作用的分子地层学,与生态地层学、事件地层学等地层学分支学科类似,其主要任务是在传统生物地层学或其他年代学框架下,提高地层划分和对比的精度。以浙江长兴煤山二叠纪-三叠纪界线地层和第四纪泥炭为例,以高分辨率的生物事件与环境事件为切入点,分别探讨在生物地层学或其他年代学框架下的分子地层工作,由此提出了分子地层学的分类单位——分子化石带。 相似文献
9.
Yang Pu Hucai Zhang Guoliang Lei Fengqin Chang Mingsheng Yang Xianyu Huang 《Frontiers of Earth Science》2009,3(3):327-335
Lipids extracted from lacustrine deposits in the paleolake Qarhan of the Qaidam basin in the northeastern Tibetan Plateau
were determined by conventional gas chromatography-mass spectrometry. Several series of biomarkers were identified, mainly
including n-alkanes, n-alkan-2-ones, n-alkanoic acids, branched alkanes, triterpenoids and steroids, indicative of various biogenic contributions. On the basis
of cluster analysis, the n-C15, n-C17, n-C19 alkanes were proposed to be derived from algae and/or photosynthetic bacteria, the n-C21, n-C23, n-C25 homologues from aquatic plants, and the n-C29, n-C31 homologues from vascular plants. In contrast, the n-C27 alkane is not categorized in the n-C29 and n-C31 group of alkanes, probably due to more complex origins including both aquatic and vascular plants, and/or differential biodegradation.
Stratigraphically, layers-2, 4 and 5 were found to show a close relationship in n-alkane distribution, associated with a positive shift in carbon isotope composition of bulk organic matter (δ13Corg), inferring a cold/dry period. Layers-1 and 6 were clustered together in association with a negative δ13Corg, excursion, probably indicating a relatively warm/humid climate. The potential coupling between the n-alkane distributions and δ13Corg, suggests a consequence of vegetation change in response to climate change, with the late MIS3 being shown to be unstable,
thought to be the climatic optimum in the Tibetan Plateau. Our results suggest that the cluster analysis used in this study
probably provides an effective and authentic method to investigate the n-alkane distribution in paleolake sediments. 相似文献
10.
Chong pom Chong lakmani 《中国地球化学学报》2010,29(2):175-181
Field investigations and laboratory integrated research as indicated that ophiolite mélange in the Nan-Uttaradit zone, northern Thailand, consists of fragments of tectonites such as metamorphic peridotite (extremely silicified serpentinite), cumulates (pyroxenolite, gabbro, and gabbro-diorite), ocean-ridge basalt, oceanic-island ba-salt and radiolarian silicalite, and it was formed during D3-P. The rock series, rock types and petrogeochemical characteristics of metamorphic tholeiites in the Nan area of the Nan-Uttaradit zone are similar to those of ocean-ridge basalts (C1) in China's Ailaoshan zone. As for the Hawaiites in the Nan area of the Nan-Uttaradit zone, their major elements, REEs and trace elements are similar to those of oceanic-island basalts in China's Jinshanjiang zone (P11). In the Uttaradit area of this zone the metamorphic alkaline basalts show transitional petrogeochemical characteristics between ocean-ridge basalts and oceanic-island basalts, which were still formed in oceanic-island environments. The above-described basalts are all oceanic volcanic rocks and they are the most important part of the Paleo-Tethys oceanic crust in the Nan-Uttaradit zone. 相似文献