黔中乌当盆地阶地沉积特征及其对盆地演化的指示

doi:10.11821/dlyj020190515

摘要/Abstract

摘要：

黔中乌当盆地是贵州省山间盆地的典型代表,四级河流阶地清晰地记录了新构造运动中区域地壳抬升和盆地演化。通过阶地沉积物砾组统计、粒度分析、光释光（OSL）测年,探讨盆地的发育和演化。结果显示,阶地砾石排列指示盆地水系古流向与现代河流基本一致,砾石磨圆度变化大,分选较差,岩性继承了区域地层。砾石组合特征反映了构造抬升期盆地内强烈的冲刷剥蚀。漫滩沉积物粒度表明盆地在稳定阶段河流水动力整体呈增大趋势。T4和T3发育阶段区域以冲刷剥蚀为主并塑造了盆地雏形。T2阶地沉积特征及测年结果（177.4 ka~87.6 ka）表明中更新世末期持续数万年的沉积夷平作用使盆地基本成型。T1阶地形成时代约25ka,指示了黔中地区最近一次构造抬升和盆地的最终定型。

关键词: 乌当盆地, 阶地, 砾组统计, 粒度分析, OSL测年

Abstract:

Studying river terrace is an important way to explore regional evolution of hydrology, paleoclimate and geomorphology. There is few reports about terraces of Guizhou because intense weathering results in poor profile preservation in this area. In Wudang Basin, a typical intermountain basin located in central Guizhou, Neotectonic movement resulted in a well-preserved sequence of four terraces, which indicates the regional crustal uplift and basin evolution clearly. In this article, measurements on gravel fabric and grain size of sediments are used to analyze the sedimentary environment of terraces. And then, combined with optical luminescence (OSL) dating, the discussion is focused on evolution age and process of Wudang Basin. The results show that in the study area, the gravels are poorly sorted and varying roundness but well orientated with river flows. The fact that lithology of gravels possess distinct inheritance indicates that they come from the surrounding stratum. Based on the gravel fabric analysis, it is concluded that the basin experienced an intense erosion during tectonic uplift. Grain size measurements on floodplain sediments present that dynamics of the rivers have an increasing tendency, which indicates regional climatic changes during a relatively tectonic stable stage. In stages of T4 and T3, there was erosion and denudation in Wudang Basin, which formed the embryo of the modern geomorphology. OSL dating shows that the age of T2 terrace is from 177.4 ka to 87.6 ka, which is consistent with the last interglacial in the sequence of Chinese glaciations and MIS5 (125 to 75 ka). So it is held that in stage of T2, warm and humid climate was important for terrace deposit up to a 10-m thickness. Based on sediment characteristics and time series, it is believed that at the late stage of Middle Pleistocene, there was a sedimentary leveling lasting for tens of thousands of years before Wudang Basin basically formed. The age of T1 terrace is about 25 ka, indicating the last tectonic uplift of Guizhou and the final shaping of Wudang Basin.

Key words: Wudang Basin, terrace, gravel fabric analysis, grain size analysis, OSL dating

蒋玺, 陈文奇, 宁凡, 郑军, 罗维均, 周涌. 黔中乌当盆地阶地沉积特征及其对盆地演化的指示[J]. 地理研究, 2020, 39(6): 1242-1254.

JIANG Xi, CHEN Wenqi, NING Fan, ZHENG Jun, LOU Weijun, ZHOU Yong. Sediment characteristics of terraces in Wudang Basin and their implications on basin evolution[J]. GEOGRAPHICAL RESEARCH, 2020, 39(6): 1242-1254.

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阶地	拔河高度(m)	阶地描述	研究分层	沉积物基本特征	研究内容	样品数 (件)
LW-T1	3.6	位于洛湾南明河东岸,上部为砂泥层,下部为砾石层	LW-T1-2	砂泥质层,局部夹少量砾石（<5%）,厚度1.7 m	粒度分析 OSL测年	17 2
LW-T1	3.6	位于洛湾南明河东岸,上部为砂泥层,下部为砾石层	LW-T1-1	砾石层,砾石含量约60%,厚度>1.2 m	砾组统计	114
LK-T2	16.0	距鱼梁河西岸约500 m,阶地顶部为砂泥层,中上部为砾石层,中部为砂泥层,下部为砾石层	LK-T2-4	砂泥质层,厚度0.3~1.5 m
			LK-T2-3	砾石层,砾石磨圆差,含量约85%,厚度0.8 m	砾组统计	133
			LK-T2-2	砂泥质层,厚度4.2 m	粒度分析 OSL测年	42 2
			LK-T2-1	砾石层,砾石含量约80%,厚度>1.6 m	砾组统计	117
YDX-T2	18.0	距渔洞河东岸约30 m,上部为砂泥层,下部为砾石层	YDX-T2-2	砂泥质层,厚度2.3 m	粒度分析 OSL测年	23 1
YDX-T2	18.0	距渔洞河东岸约30 m,上部为砂泥层,下部为砾石层	YDX-T2-1	砾石层,砾石含量约85%,厚度1.1 m	砾组统计	129
LW-T3	30.0	位于洛湾砖厂东侧,距南明河东岸约150 m	LW-T3	仅残存少量阶地沉积物,砾石、砂泥混合沉积,砾石含量约40%,厚度约0.8 m	砾组统计	109
DW-T4	57.0	距南明河约500 m,由上至下分砂泥层、粗砾石层、细砾石层、粗砾石层共4层	DW-T4-4	砂泥质层,局部夹少量砾石（<5%）,厚度1.7 m。	粒度分析	17
			DW-T4-3	砾石层,砾石粗大,磨圆好,含量约85%,厚度约2.5 m	砾组统计	116
			DW-T4-2	砾石层,砾径明显小于上下两层,砾石含量约85%,厚度约2.5 m	砾组统计	111
			DW-T4-1	砾石层,砾石粗大,磨圆好,含量约80%,厚度约3.2 m	砾组统计	134

沉积层	测点数 (个)	a轴平均走向(°)	ab面平均倾向(°)	平均倾角 (°)	最大倾角 (°)	古水流来向
LW-T1-1	58	200±	219±	22±	60	SW
LK-T2-1	58	205±	147±	25±	69	SE
LK-T2-3	26	119±	119±	12±	40	SEE
YDX-T2-1	56	165±	151±	22±	67	SE
DW-T4-1	56	145±	152±	18±	47	SE
DW-T4-2	56	166±	153±	18±	56	SE
DW-T4-3	57	177±	205±	21±	57	SSW

沉积层	砾石形态百分比(%)					砾石岩性百分比(%)
沉积层	棱角状	次棱角状	次圆状	圆状	极圆状	硅质岩	碳酸盐岩	砂岩	粉砂岩	泥质岩
LW-T1-1		29.36	26.61	44.04		21.10	55.04	16.51	6.42	0.92
LK-T2-1		18.75	19.64	55.36	6.25	21.43	43.75	34.82
LK-T2-3	39.84	48.43	11.72			8.59	47.65	3.13	9.38	31.25
YDX-T2-1	24.22	36.72	38.28	0.78		39.06	23.44	32.03	4.69	0.78
LW-T3		51.85	25.00	23.15		15.74	69.45	5.56	9.26
DW-T4-1		23.31	30.83	40.60	5.26	18.80	74.44	6.02	0.74
DW-T4-2		16.36	44.55	38.18	0.91	9.09	90.91
DW-T4-3		17.54	29.83	44.74	7.89	14.91	77.20	7.89

样品编号	埋深 (m)	U-238 (Bg/Kg)	Th-232 (Bg/Kg)	K-40 (Bg/Kg)	含水量 (%)	环境剂量率 (Gy/ka)	等效剂量 (Gy)	年龄 (ka)
LW-1	1.6	39.5±5.8	29.2±0.4	231.6±5.1	17	2.1±0.2	48.7±2.1	23.6±1.8
LW-2	0.7	55.1±7.2	39.5±0.5	282.3±6.2	18	2.7±0.2	71.2±1.7	26.7±1.8
LK-1	4.8	40.9±6.7	31.6±0.4	306.6±6.5	26	2.1±0.1	362.9±19.7	177.4±17.0
LK-2	1.8	48.1±7.1	41.1±0.5	302.0±6.4	15	2.6±0.2	301.1±25.1	114.0±11.9
YDX-1	2.3	40.7±5.9	25.6±0.4	102.2±3.4	12	1.6±0.1	138.5±7.0	87.6±6.8