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Procedia Environmental Sciences 10 ( 2011 ) 1869 – 1875
2011 3rd International Conference on Environmental Science and InformationConference Application Title Technology (ESIAT 2011) Comparative Study on the Grain Size Characteristics of Loess Deposit both on Miaodao Islands and on the Laizhou Bay plain and its implications for provenance
Xu Shujian a* and Wang Tao b
a Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, 730000, P. R. China bShandong Provincial Key Laboratory of Soil Conservation and Environmental Protection, Linyi University, Linyi, 276000, P. R. China [email protected]
Abstract
The grain size records of loess-paleosol deposit in China are some of the most important terrestrial records of the Quaternary. It systematically carried out fieldwork on loess profile of Tuoji Island on Miaodao Islands and Changyi profile on the Laizhou Bay plain, analyzed grain size of 220 and 86 samples respectively. It shows the grain size of loess in Tuoji Island profile coarser than Changyi profile. The environment-sensitive size fractions of Tuoji Island and Changyi loess section respectively are 89.1-100.0ȝm and 70.8-79.4ȝm, by analyzing grain-size class vs. standard deviation values method. The changes of grain size characteristics of loess-paleosol recorded in different sections implicated the much plentiful materials in the Changyi profile on Laizhou Bay plain than Tuoji profile on Miaodao Islands.
© 20112011 Published Published by by Elsevier Elsevier Ltd. Ltd. Selection Selection and/or and/or peer-review peer-review under under responsibility responsibility of Conference of [name organizer]ESIAT2011 Organization Committee.
Keywords: loess; grain size characteristics; environmental sensitive size fractions; Laizhou Bay plain; Miaodao Islands.
ĉ.Introduction
The extensive and continuous loess-paleosol eolian deposits in northern China, with some sections as old as 22 Ma, are an important marker of this Late Cenozoic environmental transition[1-2]. The Chinese loess-red clay archived continental-scale climatic and environmental changes during the Pliocene through Pleistocene. The Chinese loess, a widespread wind-blown deposit in northern China, covers an area of about 500,000km2 with a thickness of 150–300m [3]. The continuous loess-palaeosol deposits in northern China are divided into four stratigraphic units from the top to the bottom: Black Loam (Holocene),
1878-0296 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Conference ESIAT2011 Organization Committee. doi: 10.1016/j.proenv.2011.09.292 1870 Xu Shujian and Wang Tao / Procedia Environmental Sciences 10 ( 2011 ) 1869 – 1875
Manlan Loess (late Pleistocene), Lishi Loess (middle Pleistocene), Wucheng Loess (late Pliocene to early Pleistocene). By applying proxy indices derived from the loess–palaeosol sequences (e.g., magnetic susceptibility and grain size), changes in the East Asian monsoon can be reconstructed over the past 2.6 Ma [2]. Many studies on the grain size characteristics of loess deposits suggest that stronger winter monsoon strength generally results in coarser median grain size and coarse fraction content of loess and red clay samples [4-5]. Moreover, grain size parameters are also used to determine variations in desert extent [6, 7]. Some authors, based on ¿eld observations or grain size measurements, have suggested explicitly or implicitly that the loess formation in the Shandong area could be eolian origin [8, 9]. Some researches show that the loess mounds (a type of landforms just like a high ridge) were formed in the late period of the Late Pleistocene when Bohai sea was exposed in the period of the late warm ice age and the plain was formed, because the exposed area is not protected by vegetation, the sediments at the sea bottom are blown and transported southward by strong northern winds, and are deposited on the coastal plain [8]. However, no systematic study concerning its depositional processes and comparisons on the grain size characteristics has been done in Shandong province. In this study, we investigate a continuous loess- palaeosol sequence deposit at Tuoji Island, middle of Miaodao Islands and Changyi profile on the Laizhou Bay plain. Unlike previous studies, we carry out grain size analyses by laser diffraction particle sizer and extract environment-sensitive size fractions using grain-size class vs. standard deviation values method, and discuss further fluctuations of its implications for provenance since the last glacial epoch.
2. Materials and Methods
The Changyi loess section(36°52ƍ08ƎN, 119°24ƍ29ƎE, 8.1m above sea level) is located at Changyi city on the Laizhou Bay plain south of Bohai Sea(Fig.1). In the field outcrops, we took samples at 10-cm intervals at the loess section. A total of 86 samples were collected for grain size analyses. This area belong to Mid-latitude warm temperate monsoon climate, annual average temperature is 11.9ć , annual average precipitation is 660.1mm for the present, the terrain is higher in the north and lower in the south, the rivers such as Wei River, Yu River, Di River, are flowing from the south to the north. Having had a high deposition rate, its response to climate changes has been sensitive, and it has recorded the rapid changes of climate events during the last glaciation. Miaodao Islands, lying across the Bohai Gulf between Jiaodong Peninsula and Liaodong Peninsula, are also called Changshan Islands. They consist of 32 big and small islands, aligned in NNE direction. Because of the fall of the sea level, Miaodao Islands formed a land bridge linking Jiaodong Peninsula and Liaodong Peninsula during the Quaternary period, thus playing an important role in the development of mankind and exchange of culture. The Tuoji Island loess section (38°10ƍ49.30ƎN, 120°45ƍ23.50ƎE, 25.1m above sea level) is located at Tuoji Island, Changdao County in Shandong province (Fig. 2). In the field outcrops, we took samples at 5 cm intervals at the loess section which thickness is 900cm. A total of 181 samples were collected from the bottom to top for grain size analyses. There is a red clay deposit profile about 500m north to the loess section, we took 39 samples at 10 cm intervals at the red clay section which thickness is 390cm. This area belongs to Mid-latitude warm temperate monsoon climate, annual average temperature is 11.8ć , annual average precipitation is 560mm for the present. Having had a high deposition rate, its response to climate changes has been sensitive, and it has recorded the rapid changes of climate events during the last glaciation. The grain size of 220 samples in Tuoji Island loess section and 86 samples in Changyi loess section was determined using a Mastersizer 2000 laser grain-size meter made by Malvern Instrument Co., UK. Xu Shujian and Wang Tao / Procedia Environmental Sciences 10 (2011 ) 1869 – 1875 1871
The grain size ranged from 0.02 to 2000ȝm, with an experimental error of less than 3%. For grain size measurement, samples were pretreated by removing the organic matter and carbonate, and by heating with chemicals H2O2 and HCl, (NaPO3)6 was added and ultrasonic machine was used in order to fully separate the finer particles. They were determined at the Shandong Provincial Key Laboratory of Soil Conservation and Environmental Protection, in Department of Science & Technology of Shandong Province at Linyi University.
Fig. 1 Photo of Changyi loess section
Fig. 2 Photo of Tuoji loess section
3. Results
On the basis of field geomorphologic investigation, stratigraphic correlation, as well as absolute OSL dating, the Changyi loess–paleosol deposits are judged to have formed during the last glacial period. The grain-size distributions of loess–paleosol sequences may provide valuable information on provenance, transport and paleoclimate variability. 3.1 Grain-size curve 1872 Xu Shujian and Wang Tao / Procedia Environmental Sciences 10 ( 2011 ) 1869 – 1875
Grain-size curves of fine and coarse populations in Changyi profile are showed in Fig. 3. Obviously there is only one type grain-size distributions biomid model in this sectionˈthat is with the feature of double peaks(the higher mode and the lower mode)and one valley. Grain size distribution at 240cm and 620cm depth of Changyi profile shows the the higher mode value is about 79-89ȝm and the lower mode value is about 10ȝm, whereas the valley value appers at about 25ȝm. The grain-size curves of fine and coarse populations in Tuoji loess profile are showed in Fig. 4. Obviously there are tree grain-size distributions in Tuoji loess deposit and only one type grain-size distribution biomid model in red clay section. Grain size distribution at 225cm, 780cm and 850cm depth of loess profile in Tuoji Island shows the tree models of loess, the mode is 70.8ȝm, 56.2ȝm and 39.8ȝm respectively, and grain size distribution at 100cm,
240cm )
620cm
Volume percent(% Volume
Grain size classes˄ȝm˅
Fig. 3 Grain size distribution at 240 cm, 620 cm depth of Changyi profile
FP FP FP
˅ % ˄
Volume percent
Grain s ize˄ȝm˅
Fig. 4 Grain size distribution at 225 cm, 780 cm and 850 cm depth of Houkou loess profile in Tuoji island. 3.2 Environmental Sensitive Grain-size It is first presents the method by Boulay S to extraction environmental sensitive grain-size populations is using grain-size class vs. standard deviation values[10], then this method is widely used at marine sediment sand aeolian deposits[10-15]. Grain-size class vs. standard deviation values of 86 samples from Xulinzhuang section in Changyi City are displayed in Fig.5. One significant peak with larger standard deviations are observed at about 70.8 - 79.4ȝm, suggesting there is single environmental sensitive grain-size population in this section, so we can think above 79ȝm is the environmental sensitive grain-size population. Xu Shujian and Wang Tao / Procedia Environmental Sciences 10 (2011 ) 1869 – 1875 1873
1 79ȝm 0.8
0.6
0.4 112ȝm 50 m
Standard deviation Standard ȝ 0.2
0 1 10 100 1000 Grain size classes˄ȝm˅
Fig. 5 Grain-size classes vs. standard deviation of Changyi section Grain-size class vs. standard deviation values of 181 and 39 samples from Tuoji loess and red clay profile in Tuoji island are displayed in Fig.6. There are double modes (peaks) and one valley model at the distribution of grain-size class vs. standard deviation, the values of main peak and secondary peak of loess are 89.1-100.0ȝm and 22.1-28.1ȝm, whereas the value of valley is 44.7-50.1ȝm. Correspondingly, the peak values of red clay are 56.2-63.1ȝm and 15.9-17.8ȝm, the valley value is 25.1-28.1ȝm. One significant peak with larger standard deviations in loess are observed at about 89.1-100.0ȝm, suggesting there is single environmental sensitive grain-size population in this section, so we can think 89.1-100.0ȝm is the environmental sensitive grain-size population in loess deposit, Likewise, the environmental sensitive grain-size population in red clay profile 56.2-63.1ȝm.
Loess Red clay
Standard deviation Standard Grain size˄ȝm˅
Fig. 6 Grain-size class vs. standard deviation of Tuoji loess and red clay profile 3.3 Grain Size records Table1 give grain-size and relative percentage series of coarse and fine components at Changyi section and Tuoji section. It shows that median grain size(Md) is 75.80ȝm in Changyi profile, it is much coarser than the Md of Tuoji profile. The sand contents(>63ȝm percent) is 73.78 %, , it is also coarser than sand contents of Tuoji profile. The clay contents(<5ȝm percent) is 5.55%, , it is finer than clay contents of Tuoji profile.
Table 1. Comparison of the grain size in different profiles Changyi ProfileTuoji Profile Md/ȝm 75.80 38.01 1874 Xu Shujian and Wang Tao / Procedia Environmental Sciences 10 ( 2011 ) 1869 – 1875
Sand/% 73.78 28.30 Silt/% 20.67 61.19 Clay/% 5.55 10.51
4. Conclusions
Through investigation and analysis of Tuoji loess profile on Miaodao Islands and Changyi profile on the Laizhou Bay plain,, the following understandings are mainly obtained: (1) The grain size frequency curves of loess in Tuoji profile and Changyi profile are mainly one type of biomid, and they are eolian deposits. (2) By the method of grain-size class vs. standard deviation values, the environmental sensitive grain- size populations in Tuoji profile and Changyi profile were 89.1-100.0ȝm and 70.8-79.4ȝm. (3) The grain size of loess in Tuoji Island profile coarse than Changyi profile, The changes of grain size characteristics of loess-paleosol recorded in different sections implicated the much plentful matertals in the Changyi profile on Laizhou Bay plain than Tuoji profile on Miaodao Islands.
Acknowledgements
The project was supported by China Postdoctoral Science Foundation Funded Project (No.20100470889), Shandong Province Natural Science Foundation (No.Y2007E10), the open foundation of the Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources (No. MRE201006) and Doctoral Research start-up funding of Linyi Normal University (No. BS07010) Xu Shujian and Wang Tao / Procedia Environmental Sciences 10 (2011 ) 1869 – 1875 1875
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