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DOI	10.6038/cjg20150322
	Magnetic properties of a Miocene paleosol section in Long Reef Beach, Sydney, Australia and their environmental implications
	Wang Tao; Guo Hui; Liu Xiu-Ming; Lu Bin; Mao Xue-Gang; Zhou Zi-Bo; Wen Chang-Hui; Hou Shun-Min; Su Long-Jian
发表日期	2015
ISSN	0001-5733
卷号	58 期号:3
英文摘要	Early Miocene paleosols, dated back to 17 Ma BP, are prevalently distributed in the Sydney area, of which laterite strata was previously thought to form in tropic environments with high temperature and humidity. However, the Australia plate did not yet drift to current position during the early Miocene when Sydney paleolatitude was 45 degrees S-50 degrees S, thus belonging to the temperate zone. So, what were the paleoenvironments like during the laterite development remains controversial. In order to better understand and investigate the paleoclimate of Sydney during the early Miocene, a typical paleosol profile with laterite, located at the Long Reef Beach (LRB) town (northeast of Sydney), was taken for analysis, which was divided into three parts: Holocene part, Miocene Ultisol part and Miocene Laterite part. Environmental magnetism, an efficient approach to acquire environment information recorded by magnetic minerals, has been successfully used in study of loess-paleosols. Herein, this approach is first introduced to study the Miocene paleosol, i. e. LRB. Rock magnetic measurements on all samples (n=55) include low field magnetic susceptibility (X), saturation isothermal remanent (SIRM), saturation magnetization (M-s), anhysteretic remanent magnetization (ARM), magnetic hysteresis loops, and thermomagnetic analysis (i.e. M-T & (kappa)-T curves). Magnetic assemble in the Holocene part, which is compatible with counterparts in the Chinese loess plateau (CLP), is dominated by magnetite in the multi-domain (MD). For the Miocene Ultisol part, a trend of magnetic transformation from magnetite into maghemite against depth was observed, which coexisted with appearance of hematite. It is characteristic of higher magnetic concentration than developed paleosol in CLP and a large grain size distribution ranging from single domain (SD) to MD, and the most important is psuedo-single domain (PSD). The part of Miocene Laterite is much higher magnetic concentration and characteristic of predominant hematite with slight concentration of maghemite and goethite. The grain size of hematite is dominated by SD, at the same time showing a bit of PSD and MD. LRB Miocene paleosol is speculated to have formed in a context of exceeding rain precipitation and high temperature, where intense chemical weathering on the Earth surface occurred. The gradual alternation of magnetite into maghemite and hematite seen in the part of Miocene Ultisol can be attributed to low temperature oxidation due to eluviation caused by abundant rainfall. Maghemite, formed in the part of Miocene Ultisol, leached downwards and was transformed into stable hematite due to high temperature and recrystallization in the part of Miocene Laterite. The conversion process of magnetic minerals with increasing chemical weathering can be summarized as magnetite-magnetite core wrapped by maghemite shell-maghemite-hematite. Maghemite thermal stability was observed in a part of samples, which might be due to its coarser grain size or Fe3+ replacement by Al3+
关键词	Environmental magnetism Long Reef Beach Miocene paleosol Rock magnetism
学科领域	Geochemistry & Geophysics
语种	英语
WOS研究方向	Geochemistry & Geophysics
来源期刊	CHINESE JOURNAL OF GEOPHYSICS-CHINESE EDITION
来源机构	中国科学院西北生态环境资源研究院
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/111787
作者单位	Fujian Normal Univ, Coll Geog Sci, Key Lab Subtrop Mt Ecol, Minist Sci & Technol & Fujian Prov Funded, Fuzhou 350007, Peoples R China
推荐引用方式 GB/T 7714	Wang Tao,Guo Hui,Liu Xiu-Ming,et al. Magnetic properties of a Miocene paleosol section in Long Reef Beach, Sydney, Australia and their environmental implications[J]. 中国科学院西北生态环境资源研究院,2015,58(3).
APA	Wang Tao.,Guo Hui.,Liu Xiu-Ming.,Lu Bin.,Mao Xue-Gang.,...&Su Long-Jian.(2015).Magnetic properties of a Miocene paleosol section in Long Reef Beach, Sydney, Australia and their environmental implications.CHINESE JOURNAL OF GEOPHYSICS-CHINESE EDITION,58(3).
MLA	Wang Tao,et al."Magnetic properties of a Miocene paleosol section in Long Reef Beach, Sydney, Australia and their environmental implications".CHINESE JOURNAL OF GEOPHYSICS-CHINESE EDITION 58.3(2015).