Analysis of the Grain-size Characteristics of Dammed Lake’s Outburst Deposits: An Example from Diexi Paleolandslide-dammed Lake in the Upper Minjiang River

Abstract

Abstract:

Several burst events of Diexi paleo-lanslide-dammed lake occurred during a prehistory period (between 20 and 30 ka BP) in the upper Minjiang River, which formed an abundance of outburst deposits (appropriately 5 km in length). Based on field investigation and measurement and sampling, and laboratory sieving test, the material composition, and the grain-size distribution and parameters were analyzed. The results showed the following aspects: (1) the deposits were mainly composed of gravel, cobble, sand, and a small amount of silt and clay; (2) from the upper segment to the lower segment, the mean particle size and sorting of the deposits gradually decreased; the skewness became larger, and the kurtosis of the sediment was distributed in all the types; and (3) the grain-size frequency curves were all found to be bimodal; the granularity accumulated curves were all convex, and gradually became compact from the upper to the lower segments. These characteristics indicated that the subpopulations reflected the detrital characteristics of the source area, which was characterized by gravels as the main component. Moreover, from the upper segment to the lower segment, the gravel sediment gradually became lessened while the fine-grained sediment was found to be increased. Also, the hydrodynamic intensity of outburst floods displayed a gradually weakening, and the sorting of sediments was improved. The study results had important guiding significance for the understanding of the sedimentary characteristics and sedimentary environment of outburst deposits induced by dammed lake.

Key words: dammed lake, paleolandslide, outburst deposit, grain-size parameter, Minjiang River

CLC Number:

P642.2

MA Junxue, CHEN Jian, CUI Zhijiu, LIU Chao, CHEN Song. Analysis of the Grain-size Characteristics of Dammed Lake’s Outburst Deposits: An Example from Diexi Paleolandslide-dammed Lake in the Upper Minjiang River[J]. Geoscience, 2017, 31(06): 1261-1268.

Figures/Tables 10

Fig.1 Outline of the active tectonics in the east Tibetan Plateau and the location of the study area[19]

Fig.2 Distribution of the outburst deposits of the Diexi paleolandslide-dammed lake

Table 1 Original sample statistics (average percentage of mass per layer) for the outburst deposits in the upper segment

粒径/mm	粒径 /?	组分	质量百分比/%
			U1							U2
			U1-01	U1-02	U1-03	U1-04	U1-05	U1-06		U2-01		U2-02		U2-03		U2-04		U2-05		U2-07		U2-08		U2-09		U2-10
4~ 64	-2	砾石	69.59	51.49	53.86	46.01	46.9	48	71.83		53.04		66.74		40.59		53.66		50.13		29.95		57.53		52.15
2~ 4	-1	砂	11.57	18.82	18.88	21.92	15.57	21.92	8.03		21.92		14.48		4.35		16.47		15.09		8.73		16.59		11.19
1~ 2	0	砂	5.81	10.45	10.67	13.68	11.98	13.06	6.1		9.79		7.14		6.66		10.3		10.01		10.41		9.81		7.61
0.5~ 1	1	砂	4.47	8.31	7.07	8.7	11.5	8.37	5.4		6.08		4.36		13.04		7.78		10.33		17.48		7.79		9.41
0.25~ 0.5	2	砂	2.77	4.77	3.5	3.95	6.72	3.9	4.09		3.91		3.01		16		5.64		7.97		19.93		4.75		9.19
0.125~ 0.25	3	砂	1.94	2.63	2.13	2.27	3.66	2.1	2.7		2.67		2.38		11.88		3.29		3.41		8.86		2		5.79
0.062 5~ 0.125	4	砂	1.93	1.94	2.01	1.9	2.18	1.43	1.24		1.57		1.25		5.16		1.88		1.66		2.89		0.91		2.69
<0.062 5	8	粉/黏土	1.91	1.59	1.88	1.58	1.49	1.24	0.6		1.03		0.64		2.32		0.98		1.38		1.75		0.62		1.99

Table 2 Original sample statistics (average percentage of mass per layer) for the outburst deposits in the middle segment

粒径/mm	粒径/?	组分	质量百分比/%
			M1							M2
			M1-01	M1-02	M1-03	M1-04	M1-05	M1-06		M2-01		M2-02		M2-03		M2-05		M2-06		M2-07
4~ 64	-2	砾石	52.93	56.63	37.86	58.87	60.46	49.24	67.01		54.55		50.61		33.27		49.37		62.2
2~ 4	-1	砂	20.72	10.98	24.42	11.79	16.63	31.82	13.9		15.88		15.88		23.63		8.19		12.76
1~ 2	0	砂	11.68	7.7	15.88	8.14	9.49	12.08	6.4		9.45		11.06		17.62		6.82		7.73
0.5~ 1	1	砂	7.88	6.9	12.29	7.79	5.22	3.87	4.69		7.93		10.01		12.97		10.41		6.86
0.25~ 0.5	2	砂	3.71	5.96	5.59	6.04	2.34	1.5	2.95		5.03		5.69		7.61		11.85		4.36
0.125~ 0.25	3	砂	1.53	5.11	2.17	3.47	1.5	0.72	1.95		2.9		2.94		2.94		8.04		2.68
0.062 5~ 0.125	4	砂	0.9	3.8	1.22	2.2	1.81	0.48	1.59		2.16		1.97		1.25		3.56		1.75
< 0.062 5	8	粉/黏土	0.65	2.91	0.58	1.71	2.55	0.3	1.5		2.1		1.85		0.72		1.75		1.67

Table 3 Original sample statistics (average percentage of mass per layer) for the outburst deposits in the lower segment

粒径/mm	粒径/?	组分	质量百分比/%
			L1							L2
			L1-01	L1-02	L1-03	L1-05	L1-06	L1-07		L2-01		L2-03		L2-04		L2-05		L2-06
4~ 64	-2	砾石	54.8	45.16	36.61	26.9	53.57	57.27	55.8		47.31		41.21		62.53		46.87
2~ 4	-1	砂	14.07	23.75	25.01	29.05	14.32	22.1	16.18		21.1		24.67		11.5		15.19
1~ 2	0	砂	9.92	12.23	18.96	22.21	10.55	7.45	10.63		13.85		15.34		9.78		15.97
0.5~ 1	1	砂	8.96	8.26	10.96	10.87	8.84	2.89	8.21		9.81		9.07		8.18		14.27
0.25~ 0.5	2	砂	7.61	6.03	4.92	6.32	6.34	3.54	4.15		4.71		4.55		4.41		5.22
0.125~ 0.25	3	砂	2.78	2.53	1.85	2.65	3.44	3.24	2.22		1.85		2.43		1.89		1.42
0.062 5~ 0.125	4	砂	1.12	1.21	1.03	1.25	1.68	1.95	1.5		0.82		1.47		1.02		0.66
<0.062 5	8	粉/黏土	0.73	0.84	0.67	0.75	1.26	1.57	1.31		0.56		1.25		0.69		0.4

Table 4 Interpretations of graphical measurements (Refs. of [23-24])

粒度参数	计算公式	评判标准
平均粒径M_z	M_z= $? 16 + ? 50 + ? 84 3$	/
分选系数S_d	S_d= $? 84 - ? 16 4$ + $? 95 - ? 5 6.6$	<1.27	分选性极好
		1.27~1.41	分选性好
		1.41~1.62	分选较好
		1.62~2.00	分选中等
		2.00~4.00	分选较差
		4.00~16.0	分选差
		>16.00	分选极差
偏度S_k	S_k= $? 16 + ? 84 - 2 ? 50 2 (? 84 - ? 16)$ + $? 5 + ? 95 - 2 ? 50 2 (? 95 - ? 5)$	0.3~1.0	极负偏
		0.1~0.3	负偏
		-0.1~0.1	近对称
		-0.3~-0.1	正偏
		-1.0~-0.3	极正偏
峰度K_u	K_u= $? 95 - ? 5 2.44 (? 75 - ? 25)$	<0.67	很平坦
		0.67~0.90	平坦
		0.90~1.11	中等(正态)
		1.11~1.50	尖锐
		1.50~3.00	很尖锐
		>3.00	极尖锐

Table 4 Interpretations of graphical measurements (Refs. of [23-24])

粒度参数	计算公式	评判标准
平均粒径M_z	M_z= $? 16 + ? 50 + ? 84 3$	/
分选系数S_d	S_d= $? 84 - ? 16 4$ + $? 95 - ? 5 6.6$	<1.27	分选性极好
		1.27~1.41	分选性好
		1.41~1.62	分选较好
		1.62~2.00	分选中等
		2.00~4.00	分选较差
		4.00~16.0	分选差
		>16.00	分选极差
偏度S_k	S_k= $? 16 + ? 84 - 2 ? 50 2 (? 84 - ? 16)$ + $? 5 + ? 95 - 2 ? 50 2 (? 95 - ? 5)$	0.3~1.0	极负偏
		0.1~0.3	负偏
		-0.1~0.1	近对称
		-0.3~-0.1	正偏
		-1.0~-0.3	极正偏
峰度K_u	K_u= $? 95 - ? 5 2.44 (? 75 - ? 25)$	<0.67	很平坦
		0.67~0.90	平坦
		0.90~1.11	中等(正态)
		1.11~1.50	尖锐
		1.50~3.00	很尖锐
		>3.00	极尖锐

Table 5 Sample statistics of the logarithmic graphical measurements of the outburst deposits

分段	平均粒径M_z/mm		分选系数S_d		偏度S_k		峰度K_u
分段	变化范围	平均值	变化范围	平均值	变化范围	平均值	变化范围	平均值
上段	11.07~24.73	18.98	16.08~21.35	20.17	0.21~0.96	0.65	0.61~0.78	0.70
中段	12.79~23.47	18.33	16.92~21.02	19.82	0.31~0.90	0.67	0.63~1.25	0.75
下段	10.48~21.89	16.86	14.86~20.83	19.16	0.42~0.90	0.75	0.63~3.04	0.97

Fig.3 Grain-size distribution curves of the outburst deposits obtained using a graphic method

Fig.4 Frequency curves of the grain-size samples from the outburst deposits

Fig.5 Accumulated probability curves of the grain-size samples from the outburst deposits

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