Applicability of OSL Dating to Fine-Grained Fluvial Deposits in the Mekong River Floodplain, Cambodia

Yuji Ishii; Toru Tamura; Daniel S. Collins; Bunnarin Ben

doi:10.2478/geochr-2020-0006

Figures & Tables

(A) Map showing the drainage basin (shaded) of the Mekong River. (B) Relief map of the study area. Sampling locations for the modern flood sediments are shown by red circles, which are labelled with the residual doses of fine-grained quartz samples. The white circle represents the location of MEK-2 and MEK-2B. (C) Digital Surface Model (DSM) around the MEK-2 and MEK-2B sites. The DSM used is ALOS World 3D – 30 m (AW3D30), released from the Japan Aerospace Exploration Agency (JAXA). (D) Photograph of the section at site MEK-2B.

Examples of decay curves and dose-response curves (insets) for (A) fine-grained quartz, (B) IR50 of polymineral fine grains, (C) pIRIR150 of polymineral fine grains, and (D) pIRIR150 of K-feldspars. White points in the insets denote recycling points.

(A) Preheat plateau tests and (B) preheat dose recovery tests for samples gsj18031 (4–11 μm) and gsj18032 (62–90 μm).

Depth profiles of water content in the dry and wet seasons at site MEK-2.

Sedimentary columns of sites MEK-2 and MEK-2B. Vertical grain size profile and age-depth plots are also shown. The OSL ages are shown with 1 σ errors. The age-depth model was constructed by Bacon software (Blaauw and Christen, 2011). The dashed line shows ‘best’ model from the weighted average age and the shaded area indicates the 95% confidence interval. The single-grain ages calculated using the minimum age model (10% overdispersion value) are shown.

Quartz equivalent doses obtained from different grain size fractions of sand sample (gsj18034).

Frequency distribution of equivalent doses obtained from multi-grain measurements of (A) 62–90 μm fractions and (B) 211–250 μm fractions of gsj18034, and (C) single-grain measurements of 211–250 μm fractions of gsj18034.

Bleaching rates for OSL and IR50 of fine-grained and sand-sized samples (gsj18033 and gsj18034). The error bars represent one standard error.

Summary of dated samples and dosimetry data_ The number of measured and accepted aliquots is shown_ We added 5% to the water content values obtained from samples collected during dry season to account the seasonal changes_ The “Q”, “F”, and “P” denotes quartz, K-feldspar, and polymineral fine grains, respectively_

Laboratory code	Depth (m)	Grain size (μm)	K (%)	U (ppm)	Th (ppm)	Rb (ppm)	Water content (%)	Dose rate
Laboratory code	Depth (m)	Grain size (μm)	K (%)	U (ppm)	Th (ppm)	Rb (ppm)	Water content (%)	Quartz (Gy/ka)	F or P (Gy/ka)
*MEK-2*

gsj18025	0.85–1.00	4–11	2.2	3.0	14.9	138.0	27.5	3.79 ± 0.19	4.39 ± 0.22

gsj18026	1.90–2.05	4–11	1.4	1.9	11.2	77.7	14.0	2.93 ± 0.15	3.43 ± 0.17

gsj18027	2.90–3.05	4–11	1.6	2.3	12.6	100.0	24.8	2.99 ± 0.15	3.50 ± 0.17

gsj18028	3.85–4.00	4–11	1.5	2.1	11.8	86.6	31.4	2.61 ± 0.13	3.04 ± 0.15

gsj18029	4.90–5.05	4–11	1.7	2.5	13.7	109.0	38.9	2.86 ± 0.14	3.34 ± 0.16

*MEK-2B*

gsj18035	4.75	120–150	1.2	2.0	14.5	62.0	8.9	2.51 ± 0.15	-
gsj18035	4.75	211–250	1.2	2.0	14.5	62.0	8.9	2.45 ± 0.14	-

gsj18034	6.6	62–90	1.2	1.6	9.0	60.3	9.5	2.04 ± 0.10	2.78 ± 0.19
gsj18034	6.6	211–250	1.2	1.6	9.0	60.3	9.5	1.96 ± 0.12	2.92 ± 0.15

gsj18033	7.4	4–11	1.7	3.0	13.8	104.0	36.6	3.06 ± 0.17	3.65 ± 0.17

gsj18032	8.2	62–90	1.3	1.3	7.0	64.2	30.4	1.62 ± 0.10	2.19 ± 0.14
gsj18032	8.2	211–250	1.3	1.3	7.0	64.2	30.4	1.55 ± 0.09	2.46 ± 0.12

gsj18031	9.0	4–11	1.8	3.0	13.9	108.0	43.0	2.86 ± 0.14	3.38 ± 0.16

gsj18030	10.0	211–250	1.0	0.8	3.8	50.3	10.7	1.34 ± 0.09	-

Summaries of OSL, IRSL and post-IR IRSL SAR protocols used in this study_

Step	OSL	IRSL and post-IR IRSL
1	Preheat at 200 or 220°C for 10 s	Preheat at 180°C for 60 s
2	Blue stimulation at 125°C for 20 s	IR stimulation at 50°C for 100 s
3	Test dose	IR stimulation at 150°C for 100 s
4	Cut-heat at 160°C	Test dose
5	Blue stimulation at 125°C for 20 s	Preheat at 180°C for 60 s
6	Dose and return to step 1	IR stimulation at 50°C for 100 s
7		IR stimulation at 150°C for 100 s
8		Dose and return to step 1

Results of single-grain measurements_ The number of measured and accepted grains is shown_ The ages were calculated using central age model (CAM) and minimum age model (MAM) assuming the overdispersion values of 10% (OD = 10) and_20% (OD = 20)_ OD is calculated as part of central age model_

Laboratory code	Depth (m)	Grain size (μm)	Number of grains	CAM		MAM (OD = 10)		MAM (OD = 20)		OD (%)
Laboratory code	Depth (m)	Grain size (μm)	Number of grains	D_e (Gy)	Age (a)	D_e (Gy)	Age (a)	D_e (Gy)	Age (a)	OD (%)
*MEK-2B*

gsj18034	6.6	211–250	30 (2400)	1.49 ± 0.24	800 ± 160	1.00 ± 0.06	510 ± 40	1.15 ± 0.07	590 ± 50	81.2

gsj18032	8.2	211–250	26 (2400)	1.57 ± 0.29	960 ± 160	0.98 ± 0.05	630 ± 50	1.01 ± 0.07	650 ± 60	96.3

Luminescence ages obtained from point-bar and natural levee deposits_ “OD” is overdispersion value of quartz sample calculated using central age model_ OSL ages with errors exceeding 10 a are rounded to the nearest decade_

Laboratory code	Depth (m)	Grain size (μm)	Number of aliquots		De			Age				OD (%)
Laboratory code	Depth (m)	Grain size (μm)	Q	F or P	Quartz (Gy)	IR₅₀ (Gy)	pIRIR₁₅₀ (Gy)	Quartz (a)	Uncorrected IR₅₀ (a)	Corrected IR₅₀ (a)	Uncorrected pIRIR₁₅₀ (a)	OD (%)

*MEK-2*

gsj18025	0.85–1.00	4–11	6 (6)	6 (6)	0.7 ± 0.02	1.7 ± 0.66	-	190 ± 10	390 ± 150	480 ± 180	-	5.2

gsj18026	1.90–2.05	4–11	6 (6)	6 (6)	1.67 ± 0.04	2.32 ± 0.14	-	570 ± 30	680 ± 50	840 ± 60	-	3.6

gsj18027	2.90–3.05	4–11	6 (6)	6 (6)	1.19 ± 0.04	1.91 ± 0.06	-	400 ± 20	550 ± 30	680 ± 40	-	5.9

gsj18028	3.85–4.00	4–11	5 (6)	6 (6)	1.22 ± 0.02	1.89 ± 0.05	-	470 ± 30	620 ± 30	770 ± 40	-	0

gsj18029	4.90–5.05	4–11	6 (6)	6 (6)	1.15 ± 0.04	1.97 ± 0.09	-	400 ± 20	590 ± 40	730 ± 60	-	6.7

*MEK-2B*

gsj18035	4.75	120–150	17 (20)	-	1.36 ± 0.10	-	-	540 ± 50	-	-	-	29.9
gsj18035	4.75	211–250	17 (20)	-	1.86 ± 0.24	-	-	760 ± 110	-	-	-	52.9

gsj18034	6.6	62–90	20 (20)	6 (6)	1.24 ± 0.06	1.92 ± 0.02	11.87 ± 0.27	610 ± 50	690 ± 50	910 ± 80	4270 ± 300	22.3
gsj18034	6.6	211–250	13 (20)	6 (6)	1.75 ± 0.24	2.46 ± 0.06	9.48 ± 0.50	890 ± 130	840 ± 50	1120 ± 70	3250 ± 240	48.6

gsj18033	7.4	4–11	6 (6)	5 (6)	1.47 ± 0.02	1.96 ± 0.15	-	480 ± 30	530 ± 50	650 ± 60	-	0.9

gsj18032	8.2	62–90	20 (20)	6 (6)	0.96 ± 0.03	1.81 ± 0.03	11.42 ± 0.30	590 ± 40	830 ± 50	1100 ± 70	5220 ± 350	11.8
gsj18032	8.2	211–250	17 (20)	6 (6)	1.55 ± 0.15	2.33 ± 0.21	9.02 ± 0.67	1000 ± 110	950 ± 100	1270 ± 120	3680 ± 330	38.2

gsj18031	9.0	4–11	6 (6)	5 (6)	1.57 ± 0.03	1.84 ± 0.18	-	550 ± 30	550 ± 60	680 ± 80	-	2.3

gsj18030	10.0	211–250	17 (20)	-	1.53 ± 0.25	-	-	1150 ± 200	-	-	-	66.6

Residual doses of modern flood deposits_ The “Q”, “F”, and “P” denotes quartz, K-feldspar, and polymineral fine grains, respectively_ “OD” is overdispersion value of quartz sample calculated using central age model_

Laboratory code	Grain size (μm)	Setting	Number of aliquots		*D_e*			OD (%)
Laboratory code	Grain size (μm)	Setting	Q	F or P	Quartz (Gy)	IR₅₀ (Gy)	pIRIR₁₅₀ (Gy)	OD (%)
*MO-1*

gsj18320	4–11	levee	6 (6)	6 (6)	0.02 ± 0.00	0.79 ± 0.03	-	32.2

gsj18321	4–11	levee	6 (6)	6 (6)	0.07 ± 0.00	0.82 ± 0.03	-	3.2

*MO-2*

gsj18322	90–120	bar	20 (20)	6 (6)	0.68 ± 0.20	3.89 ± 0.24	39.5 ± 2.4	131.6
gsj18322	211–250	bar	18 (20)	6 (6)	0.32 ± 0.20	3.91 ± 1.44	28.4 ± 6.0	263.7

gsj18323	4–11	bar	6 (6)	6 (6)	0.04 ± 0.00	1.38 ± 0.05	-	16.8

gsj18324	90–120	bar	20 (20)	6 (6)	0.62 ± 0.27	4.04 ± 0.62	42.5 ± 2.8	194.1
gsj18324	211–250	bar	20 (20)	6 (6)	0.32 ± 0.15	6.11 ± 1.19	33.6 ± 2.9	202.0

*MO-3*

gsj18325	4–11	levee	6 (6)	6 (6)	0.04 ± 0.02	1.22 ± 0.05	-	101.9

*MO-4*

gsj18326	4–11	levee	6 (6)	6 (6)	0.06 ± 0.00	0.93 ± 0.04	-	17.8

gsj18327	211–250	levee	20 (20)	6 (6)	0.43 ± 0.13	1.41 ± 0.13	15.3 ± 1.0	130.0

*MO-5*

gsj18328	62–90	bar	20 (20)	6 (6)	0.49 ± 0.12	4.02 ± 0.13	39.4 ± 1.0	110.0

gsj18329	4–11	bar	6 (6)	6 (6)	1.55 ± 0.05	3.36 ± 0.20	-	7.6

*MEK-1B*

gsj18330	4–11	levee	6 (6)	6 (6)	2.43 ± 0.04	1.87 ± 0.03	-	2.3

Applicability of OSL Dating to Fine-Grained Fluvial Deposits in the Mekong River Floodplain, Cambodia

Figures & Tables

Fig. 1

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Fig. 7

Fig. 8

Summaries of OSL, IRSL and post-IR IRSL SAR protocols used in this study_

Results of single-grain measurements_ The number of measured and accepted grains is shown_ The ages were calculated using central age model (CAM) and minimum age model (MAM) assuming the overdispersion values of 10% (OD = 10) and_20% (OD = 20)_ OD is calculated as part of central age model_

Luminescence ages obtained from point-bar and natural levee deposits_ “OD” is overdispersion value of quartz sample calculated using central age model_ OSL ages with errors exceeding 10 a are rounded to the nearest decade_

Residual doses of modern flood deposits_ The “Q”, “F”, and “P” denotes quartz, K-feldspar, and polymineral fine grains, respectively_ “OD” is overdispersion value of quartz sample calculated using central age model_

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