Using soil micromorphology to assess the reliability of radiocarbon and OSL dating of fluvial deposits

Figures & data

Figure 1. A) Inset map showing the state of Tennessee (shaded) and location of the two sediment profiles within the Chickamauga Reservoir. Black point in 1A corresponds to the location of the profiles shown in 1B. B) DEM of the study area with location of the sediment profiles. C) Geologic map of the study area. Information obtained from USGS Tennessee Geologic Map Data (https://mrdata.usgs.gov/geology/state/state.php?state=TN) and DEM interpretation.

Figure 2. Stratigraphic columns and field photographs with ages obtained from AMS radiocarbon (black font) and OSL (blue font). A) profile a (cut-bank) with zoomed-in photograph of horizons 3Ab/Bt, 3BCb, and 4Ab/Bt. B) profile B (point-bar).

Figure 3. Photomicrographs of oriented soil thin sections. A) Profile A, contact between Ap and Bt, PPL. Crescent and layered clay coatings composed of clay particles and iron oxides. B) Profile A, contact between Ap and Bt, XPL. C) Profile A, contact between Ap and Bt, PPL. Crescent and layered clay coatings composed of clay particles and iron oxides. Bottom right clay coating shows direction of soil water flow downward. D) Profile A, contact between Ap and Bt, NU. Root section fluorescent under UV. E) Profile A, 4BCb, PPL. Charcoal fragment and loose sand grains. F) Profile A, 3Ab/Bt, XPL. Several crescent clay coatings fill pore walls and coating grains. Well-developed coatings can be observed as the extinction of the clay coatings is the same in several layers of clay.

Figure 4. Photographs of whole thin sections for Profile A. Dark red to brownish red features are clay coatings. Spheroidal elements with distinct circular shapes are fecal pellets. Discolorations within the same thin section correspond to evidence of bioturbation as animal burrows. Root casts and walls can be observed as elongated and irregular pore spaces. Black features correspond to fragments of charcoal. A) Contact between Ap and Bt. B) BC. C) 3Ab. D) Contact between 3BCb and 4Ab/Bt. E) Contact between 4Ab and 4Btb. F) 4BCb.

Figure 5. Photomicrographs of paleosols and alluvium horizons. A) Profile B, Bw, PPL. Very few crescent and layered clay coatings. Soil matrix surrounding mineral grains of quartz, feldspar, plagioclase, amphibole, and micas. B) Profile B, Bw, PPL. Soil matrix surrounding grains. High clay content. Charcoal fragments of sand grain size. C) Profile B, contact between Bw and E/Bt, PPL. Soil matrix surrounding mineral grains. Root section. D) Profile B, contact between Bw and E/Bt, NU. Charred root section nonfluorescent under UV. Weakly developed thin clay coatings surrounding mineral grains. Fungi Mycelium in bottom of photomicrograph, fluorescent under UV NU light. E) Profile B, E/Bt, PPL. Lithic fragment. F) Profile B, contact between 6Btb and 6BCb, XPL. Several crescent clay coatings fill pore walls and coating grains. Well-developed coatings can be observed as the extinction of the clay coatings is the same in several layers of clay.

Figure 6. Photographs of whole thin sections for Profile B. Dark red to brownish red features are clay coatings. Spheroidal elements with distinct circular shapes are fecal pellets. Discolorations within the same thin section correspond to evidence of bioturbation as animal burrows. Root casts and walls can be observed as elongated and irregular pore spaces. Black features correspond to fragments of charcoal. A) Upper Bw. B) Lower Bw. C) Contact between Bw and E/Bt. D) Upper E/Bt. E) Middle E/Bt. F) Contact between 6Btb and 6BCb.

Table 1. Radiocarbon dates on charcoal in the profiles. Note: Shaded ages shown here are interpreted as ages that are overestimated due to erosion and transport of older charcoal.

Lab	Radiocarbon lab code	Profile	Depth (cm)	Horizon	Stratigraphic context	Conventional radiocarbon age ^a Yrs B.P.	Calibrated median age ^b (ka)^c B.P.	2σ probability ranges Cal yrs B.P. (probability)	Age range with Inbuilt-age ^d Cal Yrs B.P.	Age range for comparison with OSL ^e (Yrs.)
UGAMS	37418	A	21–26	Bt	Argillic horizon	3080±20	3292 (3.3)	3230–3362 (1.000)	3130–3362	3200–3432
UGAMS	37419	A	28–33	BC	Argillic horizon with remanent features of parent material	4470±20	5093 (5.1)	4979–5008 (0.068) 5034–5092 (0.172) 5095–5140 (0.165) 5162–5283 (0.595)	4879–5283	4949–5353
UGAMS	37420	A	55–60	2Btb-2BCb	Contact between argillic horizon and argillic horizon with remanent features of parent material	6690±20	7538 (7.5)	7510–7542 (0.535) 7560–7606 (0.465)	7410–7606	7480–7676
UGAMS	37421	A	61–69	2BCb-3Ab	Contact between argillic horizon with remanent features of parent material and buried A horizon	6300±20	7208 (7.2)	7165–7229 (0.684) 7231–7264 (0.316)	7065–7264	7135–7364
UGAMS	37422	A	70–74	3BCb	Buried A horizon	4080±20	4563 (4.6)	4446–4472 (0.076) 4518–4624 (0.792) 4639–4641 (0.001) 4642–4643 (0.001) 4681–4691 (0.014) 4761–4793 (0.115)	4346–4793	4416–4863
UGAMS	37423	A	90–97	4Ab-4Btb	Contact between A horizon and argillic horizon with remanent features of parent material	4280±20	4848 (4.8)	4832–4862 (1.000)	4732–4862	4802–4932
UGAMS	37424	A	120–127	Middle 4BCb	Argillic horizon with remanent features of parent material	4430±20	5013 (5.0)	4880–4936 (0.092) 4957–5054 (0.729) 5111–5122 (0.012) 5187–5239 (0.128) 5241–5267 (0.039)	4780–5267	4850–5337
UCIAMS	222302	B	50–58	E/Bt	Horizon with lamellae	4455±20	5136 (5.1)	4972–5075 (0.390) 5101–5136 (0.102) 5166–5279 (0.508)	4872–5279	4902–5349
UCIAMS	222303	B	77–83	E/Bt	Horizon with lamellae	7870±20	8636 (8.6)	8592–8724 (0.971) 8739–8754 (0.020) 8757–8764 (0.009)	8492–8764	8462–8834
UCIAMS	222304	B	110–112	E/Bt	Horizon with lamellae	14245±20	17326 (17.2)	17126–17250 (0.241) 17252–17419 (0.759)	17026–17419	17096–17489
UCIAMS	222305	B	118–121	E/Bt	Horizon with lamellae	24420±20	28694 (28.7)	28586–28791 (1.000)	28486–28791	28556–28861
UCIAMS	222306	B	170–180	6Ab/Bt	Buried A horizon	9490±20	10736 (10.7)	10602–10615 (0.016) 10657–10785 (0.806) 10969–11001 (0.122) 11036–11062 (0.056)	10502–11062	10572–11132
UCIAMS	222307	B	190–197	6BCb	Argillic horizon with remanent features of parent material	7685±20	8459 (8.5)	8414–8524 (0.956) 8527–8537 (0.044)	8314–8537	8384–8677

^aConventional radiocarbon age is expressed with standard error in years before present (Yrs B.P.).

^bMedian probability age calculated in Calib 8.2 Software (Stuiver et al., 2020), using the IntCal20 dataset of Reimer (2020).

^cAges in parentheses are rounded to nearest century and expressed as kiloannums (ka) B.P.

^dInbuilt-age error has been added to the calibrated 2σ age range to account for the time gap between carbon fixation and the occurrence of a fire. 100 years have been added to the youngest end of the calibrated age range following Horn and Underwood (2014) and their findings for the Appalachian region.

^eDatum for all ages in the last column is 2020 CE (+70 yr added to all of the BP-1950 calibrated ages after adjusting for inbuilt age).

Table 2. Single-grain OSL ages calculated in quartz grains for the soil profiles.

Profile	Sample Horizon	Lab Code	Depth (m)	Grain-size fraction (µm)	Number of grains^1	Dose rate (Gy/kyr)	Equivalent Dose^2 ± 2σ (Gy)	Over-dispersion (%)	Single-grain OSL age ± 2σ (ka)
A	BC	USU-3028	0.30	75–150	58 (900)	2.83 ± 0.11	12.48 ± 0.86	23 ± 3	4.40 ± 0.39
A	BC replicate	USU-3371	0.30	150–250	37 (1400)	2.86 ± 0.11	13.51 ± 1.48	23 ± 4	4.72 ± 0.46
A	2Btb	USU-3029	0.55	75–150	40 (1400)	2.79 ± 0.11	12.66 ± 1.10	25 ± 4	4.54 ± 0.42
A	2Btb replicate	USU-3372	0.55	150–250	26 (1500)	2.76 ± 0.11	13.15 ± 1.93	33 ± 4	4.76 ± 0.52
A	3Ab/Bt	USU-3030	0.70	75–150	42 (900)	2.80 ± 0.11	12.78 ± 1.18	26 ± 5	4.57 ± 0.42
A	3Ab/Bt replicate	USU-3373	0.70	150–250	27 (1400)	2.72 ± 0.11	12.30 ± 2.12^3	32 ± 6	4.52 ± 0.57
A	4Btb	USU-3031	0.93	75–150	53 (900)	2.79 ± 0.11	14.33 ± 1.45	29 ± 5	5.14 ± 0.49
A	4Btb replicate	USU-3374	0.93	150–250	36 (1400)	2.72 ± 0.11	15.55 ± 1.65	24 ± 5	5.72 ± 0.55
B	Bw	USU-3375	0.25	150–250	37 (1300)	2.75 ± 0.11	0.94 ± 0.23^4	31 ± 9	0.34 ± 0.05
B	Bw replicate	USU-3379	0.25	150–250	41 (1100)	2.75 ± 0.11	0.90 ± 0.25^4	25 ± 6	0.33 ± 0.05
B	Upper E/Bt interlamellae	USU-3376	0.60	150–250	36 (1200)	2.72 ± 0.11	1.64 ± 0.22	7 ± 5	0.60 ± 0.06
B	Upper E/Bt interlamellae replicate	USU-3380	0.60	150–250	24 (1100)	2.72 ± 0.11	1.73 ± 0.28	29 ± 5	0.64 ± 0.07
B	Lower E/Bt interlamellae	USU-3377	0.97	150–250	35 (1200)	3.23 ± 0.13	1.95 ± 0.12^4	57 ± 12	0.60 ± 0.05
B	Lower E/Bt interlamellae replicate	USU-3381	0.97	150–250	34 (1100)	3.23 ± 0.11	2.16 ± 0.25	28 ± 7	0.67 ± 0.07
B	5BCb	USU-3378	1.50	150–250	31 (2000)	2.38 ± 0.11	18.15 ± 2.20	27 ± 5	7.63 ± 0.77
B	5BCb replicate	USU-3382	1.50	150–250	44 (2000)	2.38 ± 0.11	18.26 ± 1.87	30 ± 4	7.67 ± 0.73

^aAge analysis using SAR procedure following Wintle and Murray (2000) on single-grains of quartz sand (G. T. Duller, 2004). Datum for all ages is BP 2020 CE.

^bEquivalent dose (D_E) calculated using the Central Age Model (CAM) following Galbraith and Roberts (2012), unless otherwise noted.

^cEquivalent dose (D_E) calculated using the Minimum Age Model (MAM) following Galbraith and Roberts (2012).

^dEquivalent dose (D_E) calculated using the unlogged CAM following Galbraith and Roberts (2012).

Figure 7. Age-depth diagrams for the two soil profiles based on AMS radiocarbon and OSL ages from Tables 1 and 2. Error bars represent the ± 2σ errors. Black hollow circles correspond to radiocarbon ages, red color stars correspond to OSL ages. A) Profile A. B) Profile B.

Figure 8. Schematic diagram of clay coating formation in both soil profiles. A) Pedogenesis starts forming soil and soil column develops three horizons, surface soil (Ap), argillic horizon (Bt), and parent material with argillic horizon features (BC). K-feldspar (Kfs), plagioclase (Pl), and muscovite (Ms) start to weather into clay minerals. Clay particles are also available as sediment load from the river. Clay particles travel downward when water infiltrates the soil. During drying periods, clay particles adhere parallel to mineral grain and biopore surfaces, forming clay coatings. B) a depositional event buries the initial soil column, and pedogenesis starts to act in the new fluvial deposits and continues to act in the initial fluvial deposits. Kfs, Pl, and Ms continue to chemically weather into clay minerals, that together with clay carried as suspended sediment from the river continue traveling downwards with water infiltration. New clay coatings form in mineral grain and biopore surfaces in the newer deposits. Older clay coatings receive more clay particles that keep adding and forming thick, and well-developed clay coatings. High permeability, porosity, and well-drained soils allow the newer and the older fluvial deposits to be connected after depositional events.

Table

Soil or paleosol	Depth	Description
Profile A (cut-bank)
Ap	0–19 cm	Topsoil. Dark brown (10 YR 3/3) sandy loam; weak subangular blocky ped structure, friable; many fine roots and several wide roots, abundant plant activity; clear and crenulated boundary.
Bt	19–29 cm	Light dark brown (10 YR 4/4) sandy loam; weak subangular blocky structure, friable; some fine roots; abrupt and wavy boundary. Illuviated clay as clay coatings observed in thin section.
BC	29–41.5 cm	Light dark brown (10 YR 3/4) silt loam; weak subangular blocky ped structure; friable; abrupt and crenulated boundary. Illuviated clay as clay coatings observed in thin section.
2Ab/Bt	41.5–46 cm	Buried A horizon. Dark brown (10 YR 3/3) sandy loam; single grain structure; very friable; abrupt and wavy boundary.
2Btb	46–57 cm	Light dark brown (10 YR 4/4) sandy loam; weak subangular blocky ped structure; friable; abrupt and crenulated boundary. Illuviated clay as clay coatings observed in thin section.
2BCb	57–63 cm	Yellowish dark brown (10 YR 4/6) sandy loam; weak subangular blocky structure; friable to very friable; abrupt and wavy boundary. Illuviated clay as clay coatings observed in thin section.
3Ab/Bt	63–74 cm	Buried A horizon. Dark brown (10 YR 3/3) sandy loam; angular blocky ped structure; firm; iron oxide staining; abrupt and crenulated boundary.
3BCb	74–83 cm	Bronze (10 YR 4/6) sandy loam; granular structure; very friable consistence; iron oxide staining; abrupt and wavy boundary. Illuviated clay as clay coatings observed in thin section.
4Ab/Bt	83–93 cm	Buried A horizon. Dark brown (10 YR 3/3) sandy loam; weak angular blocky ped structure; friable; abrupt and crenulated boundary.
4Btb	93–106 cm	Yellowish dark brown (10 YR 4/6) sandy loam; strong angular blocky ped structure; very friable; abrupt and smooth boundary. Illuviated clay as clay coatings observed in thin section.
4BCb	106–132 cm	Light dark brown (10 YR 3/4) sandy loam; granular structure; firm; abrupt boundary. Illuviated clay as clay coatings observed in thin section.
Profile B (Point-bar)
Ap	0–12.5 cm	Topsoil. Very dark brown (10 YR 3/2) fine sandy loam; granular to weak subangular blocky ped structure; very friable; many thin and wide roots, abundant plant activity; clear and smooth boundary.
Bw	12.5–45 cm	Yellowish dark brown (10 YR 4/6) sandy loam; granular to weak subangular blocky ped structure; very friable; several thin roots; clear and smooth boundary.
E/Bt	45–130.5 cm	Light dark brown (10 YR 3/4) fine sandy loam; angular blocky ped structure; firm; some thin roots; clear and smooth boundary. Presence of dark colored lamellae in this horizon. Translocated clay observed in thin section.
5Ab/Bt	130.5–147 cm	Buried A horizon. Light dark brown (10 YR 4/4) loam; angular blocky ped structure; firm; clear and smooth boundary.
5BCb	147–153.5 cm	Light dark brown (10 YR 4/4) sandy loam; strong angular blocky ped structure; firm; clear and wavy boundary. Illuviated clay as clay coatings observed in thin section.
6Ab/Bt	153.5–165 cm	Buried A horizon. Light dark brown (10 YR 4/4) sandy loam; angular blocky structure; friable; abrupt and wavy boundary. Illuviated clay as clay coatings observed in thin section.
6Btb	165–176 cm	Yellowish dark brown (10 YR 4/6) sandy loam; subangular blocky ped structure; friable consistence; abrupt and wavy boundary. Illuviated clay as clay coatings observed in thin section.
6BCb	176–197 cm	Light dark brown (10 YR 4/4) loam; angular blocky ped structure; friable to slightly firm consistence; roots casts extending downward. Illuviated clay as clay coatings observed in thin section.

Table

Grain size distribution (wt%)
Soil horizon	Clay	Silt	Very fine sand	Fine sand	Medium sand	Coarse sand	Very coarse sand
Profile A (cut-bank)
Ap	5.7	35.2	25.2	25.2	8.6	0.2	0.00
Bt	5.6	31.9	25.0	27.3	10.1	0.1	0.00
Bt	11.3	53.3	23.4	9.4	1.8	0.8	0.00
BC	5.2	32.1	26.4	27.1	9.1	0.2	0.00
2Ab/Bt	5.1	29.8	26.9	28.0	9.7	0.4	0.00
2Btb	5.0	31.4	26.7	27.6	9.1	0.2	0.00
2BCb	4.4	28.7	27.2	29.5	10.1	0.2	0.00
3Ab/Bt	5.5	30.5	28.0	27.0	8.7	0.3	0.00
3Ab/Bt	5.4	31.3	31.1	25.3	6.7	0.2	0.00
3BCb	3.7	23.1	30.1	33.0	10.0	0.2	0.00
4Ab/Bt	4.8	29.8	28.3	28.0	8.9	0.3	0.00
4Btb	5.4	31.0	28.4	26.9	8.2	0.2	0.00
4Btb	5.5	33.1	28.0	25.6	7.7	0.2	0.00
4Btb	6.2	34.4	27.4	25.6	6.4	0.0	0.00
4BCb	6.0	34.4	28.0	25.2	6.4	0.1	0.00
4BCb	7.1	38.8	27.2	21.2	5.5	0.2	0.00
Profile B (point-bar)
Ap*	-	-	-	-	-	-	-
Bw*	-	-	-	-	-	-	-
E/Bt	6.18	38.01	28.29	22.07	5.16	0.28	0.00
E/Bt	6.72	42.48	28.20	18.75	3.80	0.05	0.00
E/Bt	6.60	41.17	29.04	19.50	3.55	0.14	0.00
E/Bt	6.00	37.43	29.44	22.51	4.49	0.13	0.00
Lamellae	5.77	37.11	28.76	23.07	5.19	0.10	0.00
E/Bt	5.85	37.05	27.96	23.34	5.70	0.09	0.00
Lamellae	5.87	37.46	25.66	23.37	7.45	0.20	0.00
E/Bt	4.83	32.11	24.68	27.70	10.40	0.28	0.00
Lamellae	4.33	29.60	24.20	29.37	11.95	0.55	0.00
E/Bt	3.82	27.23	24.51	31.31	12.67	0.46	0.00
E/Bt	3.79	25.68	25.64	32.36	12.20	0.33	0.00
E/Bt	4.07	27.71	26.62	30.19	10.94	0.47	0.00
5Ab/Bt	4.40	30.63	27.80	27.83	9.14	0.19	0.00
5BCb	4.39	29.04	23.48	28.05	14.15	0.89	0.00
6Ab/Bt	6.09	37.98	21.81	19.92	13.03	1.17	0.00
6Btb	3.05	24.71	16.26	28.82	24.60	2.57	0.00
6BCb	7.07	39.13	21.58	20.36	11.06	0.79	0.00

*Ap and Bw horizons in profile B were significantly mixed by plant roots and the horizons were hanging from the roots. Bulk samples from these two horizons were not taken, but a differentiation between the modern topsoil and the underlying Bw horizon was visible.

PROFILE A, SAMPLE BC (USU-3028), n = 58 (900).

PROFILE A, SAMPLE BC replicate (USU-3371), n = 37 (1400).

PROFILE A, SAMPLE 2Btb (USU-3029), n = 40 (1400).

PROFILE A, SAMPLE 2Btb replicate (USU-3372), n = 26 (1500).

PROFILE A, SAMPLE 3Ab/Bt (USU-3030), n = 42 (900).

PROFILE A, SAMPLE 3Ab/Bt replicate (USU-3373), n = 27 (1400).

PROFILE A, SAMPLE 4Btb (USU-3031), n = 53 (900).

PROFILE A, SAMPLE 4Btb replicate (USU-3374), n = 36 (1400).

PROFILE B, SAMPLE Bw (USU-3375), n = 37 (1300).

PROFILE B, SAMPLE Bw replicate (USU-3379), n = 41 (1100).

PROFILE B, SAMPLE Upper E/Bt interlamellae (USU-3376), n = 36 (1200).

PROFILE B, SAMPLE Upper E/Bt interlamellae replicate (USU-3380), n = 24 (1100).

PROFILE B, SAMPLE Lower E/Bt interlamellae (USU-3377), n = 35 (1200).

PROFILE B, SAMPLE Lower E/Bt interlamellae replicate (USU-3381), n = 34 (1100).

PROFILE B, SAMPLE 5Bcb (USU-3378), n = 31 (2000).

PROFILE B, SAMPLE 5Bcb replicate (USU-3382), n = 44 (2000).

Table

Profile	Sample Horizon	Lab Code	In-situ water content^1 (%)	Dose rate horizons	Gamma DR proportion^2	K (%)^3	Rb (ppm) ^3	Th (ppm) ^3	U (ppm) ^3	Cosmic (Gy/kyr)
A	BC	USU-3028	16.8	BC2 C2 BC3	0.25 0.45 0.30	1.74 ± 0.04 1.75 ± 0.04 1.68 ± 0.04	75.9 ± 3.0 81.4 ± 3.3 83.4 ± 3.3	10.1 ± 0.9 10.3 ± 0.9 11.0 ± 1.0	2.3 ± 0.2 2.4 ± 0.2 2.4 ± 0.2	0.21 ± 0.02
A	BC replicate	USU-3371	13.5	C BC2	0.50 0.50	1.84 ± 0.05 1.74 ± 0.04	75.9 ± 3.0 76.9 ± 3.1	10.1 ± 0.9 10.3 ± 0.9	2.3 ± 0.2 2.4 ± 0.2	0.21 ± 0.02
A	2Btb	USU-3029	21.2	BC3 C3 BC4	0.30 0.50 0.20	1.68 ± 0.04 1.75 ± 0.04 1.80 ± 0.04	83.4 ± 3.3 77.1 ± 3.1 84.8 ± 3.4	11.0 ± 1.0 10.0 ± 0.9 10.6 ± 1.0	2.2 ± 0.2 2.4 ± 0.2 2.3 ± 0.2	0.20 ± 0.02
A	2Btb replicate	USU-3372	18.6	BC3 C3 BC4	0.25 0.45 0.30	1.74 ± 0.04 1.75 ± 0.04 1.68 ± 0.04	75.9 ± 3.0 81.4 ± 3.3 83.4 ± 3.3	10.1 ± 0.9 10.3 ± 0.9 11.0 ± 1.0	2.3 ± 0.2 2.4 ± 0.2 2.4 ± 0.2	0.21 ± 0.02
A	3Ab/Bt	USU-3030	23.2	BC4 C4 BC5	0.30 0.30 0.40	1.80 ± 0.05 1.73 ± 0.04 1.80 ± 0.05	84.8 ± 3.4 74.3 ± 3.0 83.5 ± 3.3	10.6 ± 1.0 10.1 ± 0.9 11.1 ± 1.0	2.3 ± 0.2 2.2 ± 0.2 2.5 ± 0.2	0.19 ± 0.02
A	3Ab/Bt replicate	USU-3373	22.9	BC4 C4 BC5	0.30 0.50 0.20	1.68 ± 0.04 1.75 ± 0.04 1.80 ± 0.05	83.4 ± 3.3 77.1 ± 3.1 84.8 ± 3.4	11.0 ± 1.0 10.0 ± 0.9 10.6 ± 1.0	2.4 ± 0.2 2.2 ± 0.2 2.3 ± 0.2	0.20 ± 0.02
A	4Btb	USU-3031	22.6	BC5 C5 BC6	0.35 0.35 0.30	1.68 ± 0.04 1.75 ± 0.04 1.80 ± 0.05	83.4 ± 3.3 77.1 ± 3.1 84.8 ± 3.4	11.0 ± 1.0 10.0 ± 0.9 10.6 ± 1.0	2.4 ± 0.2 2.2 ± 0.2 2.3 ± 0.2	0.20 ± 0.02
A	4Btb replicate	USU-3374	23.2	BC5 C5 BC6	0.35 0.35 0.30	1.80 ± 0.05 1.79 ± 0.04 1.77 ± 0.04	83.5 ± 3.3 73.1 ± 2.9 72.4 ± 2.9	11.1 ± 1.0 9.4 ± 0.8 9.3 ± 0.8	2.5 ± 0.2 2.2 ± 0.2 2.2 ± 0.2	0.19 ± 0.02
B	Bw	USU-3375	10.4	Ap Bw Bw/C2	0.25 0.50 0.25	1.47 ± 0.04 1.64 ± 0.04 1.96 ± 0.04	57.7 ± 2.3 65.4 ± 2.6 81.1 ± 3.3	9.1 ± 0.8 9.9 ± 0.9 9.7 ± 0.9	2.1 ± 0.1 2.3 ± 0.2 2.6 ± 0.2	0.21 ± 0.02
B	Bw replicate	USU-3379	10.1	Ap Bw Bw/C2	0.25 0.50 0.25	1.47 ± 0.04 1.64 ± 0.04 1.96 ± 0.04	57.7 ± 2.3 65.4 ± 2.6 81.1 ± 3.3	9.1 ± 0.8 9.9 ± 0.9 9.7 ± 0.9	2.1 ± 0.1 2.3 ± 0.2 2.6 ± 0.2	0.21 ± 0.02
B	Upper E/Bt Interlamellae	USU-3376	11.8	Bw/C2 C2 Bw/C3 C3	0.25 0.50 0.125 0.125	1.96 ± 0.05 1.74 ± 0.04 1.93 ± 0.05 2.15 ± 0.05	82.1 ± 3.3 70.1 ± 2.8 80.6 ± 3.2 97.5 ± 3.9	9.7 ± 0.9 8.0 ± 0.7 9.9 ± 0.9 12.0 ± 1.1	2.6 ± 0.2 2.0 ± 0.1 2.5 ± 0.2 2.9 ± 0.2	0.21 ± 0.02
B	Upper E/Bt Interlamellae replicate	USU-3380	11.9	Bw/C2 C2 Bw/C3 C3	0.25 0.50 0.125 0.125	1.96 ± 0.05 1.74 ± 0.04 1.93 ± 0.05 2.15 ± 0.05	82.1 ± 3.3 70.1 ± 2.8 80.6 ± 3.2 97.5 ± 3.9	9.7 ± 0.9 8.0 ± 0.7 9.9 ± 0.9 12.0 ± 1.1	2.6 ± 0.2 2.0 ± 0.1 2.5 ± 0.2 2.9 ± 0.2	0.21 ± 0.02
B	Lower E/Bt Interlamellae	USU-3377	14.2	C2 Bw/C3 C3 Bw/C4	0.25 0.50 0.125 0.125	1.93 ± 0.05 2.15 ± 0.05 2.07 ± 0.05 1.74 ± 0.04	80.6 ± 3.2 97.5 ± 3.9 96.4 ± 3.9 70.1 ± 2.8	9.9 ± 0.9 12.0 ± 1.1 12.9 ± 1.2 8.0 ± 0.7	2.5 ± 0.2 2.9 ± 0.2 2.9 ± 0.2 2.0 ± 0.1	0.20 ± 0.02
B	Lower E/Bt Interlamellae replicate	USU-3381	14.2	C2 Bw/C3 C3 Bw/C4	0.25 0.50 0.125 0.125	1.93 ± 0.05 2.15 ± 0.05 2.07 ± 0.05 1.74 ± 0.04	80.6 ± 3.2 97.5 ± 3.9 96.4 ± 3.9 70.1 ± 2.8	9.9 ± 0.9 12.0 ± 1.1 12.9 ± 1.2 8.0 ± 0.7	2.5 ± 0.2 2.9 ± 0.2 2.9 ± 0.2 2.0 ± 0.1	0.20 ± 0.02
B	5BCb	USU-3378	15.6	BC5 C5 BC6	0.25 0.50 0.25	1.65 ± 0.04 1.52 ± 0.04 1.47 ± 0.04	64.3 ± 2.6 57.6 ± 2.3 57.7 ± 2.3	9.3 ± 0.8 8.7 ± 0.8 9.1 ± 0.8	2.2 ± 0.2 2.0 ± 0.1 2.1 ± 0.1	0.18 ± 0.02
B	5BCb replicate	USU-3382	15.4	BC5 C5 BC6	0.25 0.50 0.25	1.65 ± 0.04 1.52 ± 0.04 1.47 ± 0.04	64.3 ± 2.6 57.6 ± 2.3 57.7 ± 2.3	9.3 ± 0.8 8.7 ± 0.8 9.1 ± 0.8	2.2 ± 0.2 2.0 ± 0.1 2.1 ± 0.1	0.18 ± 0.02

^aFor profile A samples, 15.0 ± 3.0% applied as water content in dose rate calculation. For profile B, the average of each pair is used as water content in dose rate calculation.

^bProportions used in gamma dose rate calculation. Beta dose rate is derived from Bw horizon minus De sample unit.

^cElemental concentrations determined using ICP-MS and ICP-AES techniques; dose rate is derived from concentrations by conversion factors from Guérin et al. (2011).

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Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.