Analysis on sedimentary cycle characteristics of the late pleistocene section in xiadian, sanhe

Scientific Journal of Earth Science December 2014, Volume 4, Issue 4, PP.191-195

Analysis on Sedimentary Cycle Characteristics of the Late Pleistocene Section in Xiadian, Sanhe Zhirong Liu, Jun Shen, Jingyi Huang, Yanping Wang, Xiaohui Yu* Institute of Disaster Prevention Science and Technology, Beijing 101601, China

Abstract Through detailed measurement of the late Pleistocene section in Xiadian, Sanhe, combined with sedimentare lithology, sedimentary structures and dating results, research on the characteristics of cyclic sedimentation is carried out. The results show that the strata in Sanhe, Hebei Province formed at 12~20Ka, belonging to the late Pleistocene; the strata of this section is composed of a series of “fine sand-silt” and “silt-clay” cycles; and there are two possible causes about the sedimentary cycles: change of river course, or climate change, further studies are needed to determine the cause of sedimentary cycles.

Keywords: The Late Pleistocene; Sedimentary Cycle; Change of River Course

1 INTRODUCTION Xiadian, in Sanhe county , Hebei province is well-known by geologist by the 8-magnitude earquake in 1679, then a lot seismological research were carried out. However, researcher didn’t pay sufficient attention on stratigraphy and sedimentary aspects. This paper study on the sedimentary characteristics of the late Pleistocene stratigraphic cycles, and then determines the sedimentary environment and influencing factors.

2 SURVEY OF THE STUDY AREA Xiadian is located in the alluvial plain of Chaobai river, eastern Beijing, belonging to the Dachang sunken in geological structure (Fig 1). Due to the impact of Xiadian normal dip slip movement, Dachang sunken continuous subsidence, in which deposit about 600~700m thick quaternary loose sediments. The main landform in late Pleistocene is fine grained deposits of meandering river, with fine packing, unconsolidated fine sand, silt and clay.

Fine sand and silt, can be used as building material. There is one artificial scarp, locating in the lower wall of the Sanhe-Pinggu fault, vertical drop of 10 meters. The specific location of the scarp is latitude 39°58′27.6", the east longitude 116°55′50.03", and the strata occurrence is nearly horizontal, developing vertical joint(Fig 2).

3 MEASURED STRATIGRAPHIC SECTIONS The starting point coordinates of measured stratigraphic section is: N39°58′27.60″ and the end coordinates: N39°58′27.60″ E116°55′52.94″.

Measured stratigraphic sections from top to bottom are described as follows: (1) Silty clay, brown, with rust spots, loose, developing plant root( modern soil layer), the layer may be for the artificial accumulation layer…………………………………………………………………………………0.24m (2) Shallow brown clayey silt with rust spots, semi-consolidated, medium layered, bedding agenesis …………………………………………………………………………………………………………….…0.15m (3) Brown silty clay with rust spots, thin bed………………………………………………………………...…0.03m *

Supported by Narural Science Fund Project (41372216) and Central University team innovation Project (ZY20120102) - 191 http://www.j-es.org

(4) Brown clayey silt with rust spots, silty sand fine practices, medium layered, bedding is not development…………………………………………………………………………………………………0.26m

FIG.1 PROFILE AND MAJOR GEOLOGICAL FEATURES IN XIADIAN, SANHE COUNTY ( ACCORDING TO GAO ZHANWU, 2001, MODIFIED)

FIG.2 PHOTO OF THE SECTION SCARPS, IN XIADIAN - 192 http://www.j-es.org

(5) Shallow brown silty sand with rust spots, no bedding, the layer is obvious different from the overlying and underlying strata…………………………………………………………………………………………..…0.73m (6) Brown silty clay, the hand rubs into the mud. The layer is obvious different from the underlying and overlying strata after weathering, the layer distribution is stable, then can be used as a marker of transverse contrast layer……………………………………………………………………………………………………….…0.16m (7) Brown clayey silt with rust spots and plant roots, clay content is higher than 25%, with compaction…………………………………………………………………………………………….….…1.38m (8) Grey brown Silty clay………………………………………………………………………………….……0.40m (9) Thin interbedded silty sand and clay layer, developing horizontal bedding, occasionally inclined bedding. A layer of clay and silt in the formation of light and shade different bands, the layer is formed of wet and dry different bands in the weathered surface, fine particles of wet strip, dry strip for silty sand……………………………………………………………………………………………………….…0.66m (10) Yellowish-brown silty clay, relatively loose, medium thick bedded, with apparent boundary with the overlying layer and underlying layer……………………………………………………………………………….…0.80m (11) Yellowish-brown clayey silt with rust spots, loose, with silty patch , fawn, hand rubbing a greasy feeling…………………………………………………………………………………………………….…0.55m (12) Deep brown clay, can be a marker bed, horizontal bedding. High content of clay lead to fragmentation or a garlic like after weathering……………………………………………………………………………….…0.30m (13) Silty clay containing snail fossils, loose. The top layer of clay content is significantly higher than that in the lower part, clamping 8-9cm brown silty sand layer, horizontal bedding not development, and in which there are snail fossils……………………………………………………………………………………………..……1.28m (14) Brown muddy silty sand with snail fossils and rust spots with compaction…………………………..……1.16m (15) Pale yellow brown fine sand with clay, with fine horizontal bedding. Particle is changed from thin to thick form the upper layer to lower layer, and the upper surface is uneven erosion discontinuity…………………………………………………………………………………………………0.37m (16) Pale yellow brown Silt to fine sand with fine horizontal bedding, good sorting, grinding medium, mainly consist of quartz, feldspar, and other dark minerals……………………………………………………..…0.42m (17) Brown fine sand with rusts spots, developing horizontal bedding, containing 10% clay ………………………………………………………………………………………………………..…….0.20m (18) Brown fine and silty sand, developing horizontal bedding, cross bedding and wavy bedding, the monolayer thickness of 0.5-1cm………………………………………………………………………………………..0.40m (19) Grey brown medium thick bedded fine sand, with no bedding………………………………………….…0.25m (20) Grey brown sandy clay, outcropped thickness of 10cm, containing organic matter and ancient vertebrate fossils, hand rub the clay into the mud……………………………………………………………………..Bottoming out Total thickness of 9.76m The second layer of the OSL age is 12.23±1.32Ka, and the nineteenth layers of the OSL age is 19.35±2.10ka.

Therefore this section belongs to late Pleistocene. (Ages tested by the Key Laboratory of Crust Dynamics, the Institute of Crustal Dynamics)

4 SEDIMENTARY CHARATERISTICS OF CYCLES According to the observation, measurement and indoor comprehensive analysis of the stratigraphic section, it reach a conclusion that late Pleistocene in Xiadian, Sanhe, is meandering river sedimentary environment. In addition to the - 193 http://www.j-es.org

first artificial bed and the twentieth bed (no bottoming), High frequency cycle statistics suggest that the section is mainly composed of 6 coarse-fine cycles (Fig 3), and each cycle consists of a combination of deposition causes related.

FIG. 3THE STRATA HISTOGRAM AND SEDIMENTARY CYLCES OF THE LATE PLEISTOCENE SECTION IN XIADIAN, SANHE

4.1 Fine Sand-Silt Cycle In the lower part of the section, the 15-19 layers, the lower part of the cycle is fine sand or fine sand with silt, with rust spots, and the upper part is siltstone, the overall upward tapering.

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4.2 Silt-Clay Cycle Sedimentary cycles of the late Plieocene section in Xiadian, Sanhe are dominated by Silt-clay cycle, and the overall features are the lower part of the cycle is silt or muddy silty sand, silt contene reduced upward, gradually transition to silty clay or clay, the overall upward tapering too.

5 ANALYSIS OF CYCLES There are two possible reasons for the formation of cycles.

One is the swing of Chaobai River. As everyone knows that river has a typical dual structure, the upper part thin and the lower part coarse. Therefore, transformation of the meandering river can be superimposed to form a plurality of positive cycles from coarse to fine, and which is consistent with the characteristics of the sedimentary cycle of of the late Plieocene section in Xiadian, Sanhe.

The other is climate change. We know that the cold and warm, dry and wet climate alternately changed during the late glacial peak ( about 10~23ka),which also can form a plurality of positive cycles from coarse to fine.

So the causes of the sedimentary cycles of the late Plieocene section in Xiadian, Sanhe need further study.

6 CONCLUSIONS â‘ The late Plieocene section in Xiadian, Sanhe is mainly composed of fine sand, silt and clay. There are two types of sedimentary cycle, respectively fine sand-silt cycle and silt-clay cycle, tapering upward. â‘Ą There are two possible origins of the sedimentary cycles of the late Plieocene section in Xiadian, Sanhe. One is change of river course, the other is climate change. The exact cause remains to be further studied.

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[2]

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[5]

Liu Baojin, Zhang Xiankang, Chen Yong, Feng Shaoying, Ji Jifa, Yuan Hongke, Zuo Ying. Research on crustal structure and active fault in the Sanhe-Pinggu earthquake(M8.0) zone based on single-fold deep seismic reflection and shallow seismic reflection profiling. Chinese Journal of Geophysics, 2011, 54(5): 1251-1259

AUTHORS 1

Zhirong Liu, born in February 1978 Hebei

3

Jingyi Huang, female, the Han nationality, Master, Lecture,

province, female, the Han nationality, Phd

mainly engaged in Mineralogy and Mineral deposit geology.

in Paleontology and Stratigraphy in June

Email: 50645345@qq.com.

2007 from China University of Geosciences

4

(Beijing).

Associate

professor

mainly

engaged in Sedimentology and Stratigraphy.

Email: 13069615@qq.com.

Yanping Wang, female, the Han nationality, Doctor, Associate

professor, mainly engaged in Remote sensing geology.

Email: 327829751@qq.com.

5

2

Jun Shen, male, the Han nationality, Doctor, Professor, mainly

engaged in Seismic geology and Remote sensing geology.

Email: Amethy10@163.com

Xiaohui Yu, male, the Han nationality, Master, Lecture, mainly

engaged in Petrology and Seismic geology.

Email: 4325551@qq.com.

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