240+239Pu depositional signatures as a viable geochronological tool in the Amazon Basin

Luciana M Sanders; Kathryn H Taffs; Debra Stokes; Alex Enrich-Prast; Christian J Sanders

doi:10.1515/geochr-2015-0068

Figures & Tables

Study area: A) South America; B) Porto Velho region showing study sites RM, PP, PZC floodplain lakes adjacent to the Madeira River and; C) Santarem region showing study sites PA2 and PA9 floodplain lakes located near the Tapajos River, PA10 sediment core from a floodplain lake directly influenced by the Amazon River.

239+240Pu, 210Pb, 226Ra and 210Pbex profiles from the six sediment cores in this work. The first occurrence of 239+240Pu indicates ~1950 when these radionuclides were first introduced into the atmosphere. The ~1950 mark on the 210Pbex profiles are based on the sediment accumulation rates dated through the Constant Initial Concentration (CIC) approach (Appleby and Oldfield, 1992). PP, PZC, RM, PA2, PA9, PA10 - study sites.

Sediment accumulation rates (mm year-1) and inventories (mBq cm-2)based on the 210Pb and 239+240Pu sediment dating methods_

StudySite	²¹⁰Pb(mm year^-1)	²¹⁰PbBq cm^-2	^239+240Pu(mm year^-1)	^239+240Pu(mBq cm^-2)	MajorRiver
PA2	2.7	6.5	2.4	4.9	Tapajos
PA9	18.6	7.0	10.2	1.0	Tapajos
PA10	8.2	53.6	2.3	0.5	Amazon
PP	6.2	22.4	3.4	2.7	Madeiras
PZC	5.8	3.1	4.2	2.0	Madeiras
RM	6.1	40.2	6.2	3.7	Madeiras

Depth profiles of dry bulk density (DBD) (g cm-3) and mass accumulation rates (MAR) (g cm-2year-1) of the six sediment cores (PA2, PA9, PA10, RM, PP, PZC) studied in this work_

Depth (cm)	PA2		PA9		PA10		RM		PP		PZC
Depth (cm)	DBD	MAR	DBD	MAR	DBD	MAR	DBD	MAR	DBD	MAR	DBD	MAR
0–2	0.54	0.18	0.48	0.53	1.01	0.34	0.65	0.37	0.89	0.28	0.74	0.33
2–4	0.55	0.19	0.53	0.58	0.89	0.30	0.63	0.36	0.81	0.26	0.56	0.25
4–6	0.58	0.20	0.60	0.66	1.03	0.35	0.77	0.44	0.83	0.26	0.62	0.28
6–8	0.59	0.20	0.56	0.61	1.07	0.36	0.69	0.39	0.84	0.27	0.72	0.32
8–10	0.62	0.21	0.58	0.63	1.04	0.35	0.71	0.40	0.77	0.25	0.72	0.32
10–12	0.61	0.21	0.59	0.65	1.05	0.36	0.75	0.43	0.78	0.25	0.76	0.34
12–14	0.57	0.19	0.63	0.70	1.14	0.39	0.70	0.40	0.94	0.30	0.72	0.32
14–16	0.62	0.21	0.66	0.72	1.10	0.37	0.68	0.39	1.02	0.33	0.91	0.41
16–18	0.58	0.20	0.63	0.69	0.99	0.34	0.66	0.37	1.05	0.33	0.71	0.32
18–20	0.57	0.19	0.62	0.68	1.07	0.36	0.64	0.36	1.00	0.32	0.77	0.34
20–22	0.59	0.20	0.63	0.70	0.96	0.33	0.74	0.42	0.90	0.29	0.78	0.35
22–24	0.59	0.20	0.62	0.68	1.00	0.34	0.70	0.40	1.06	0.34	0.72	0.32
24–26	0.58	0.20	0.61	0.68	0.97	0.33	0.67	0.38	1.00	0.32	0.81	0.37
26–28	0.58	0.20	0.66	0.73	1.05	0.36	0.77	0.44	0.94	0.30	0.96	0.43
28–30	0.59	0.20	0.72	0.79	0.95	0.32	0.71	0.40	0.96	0.31	0.81	0.37
30–32	0.62	0.21	0.71	0.78	0.95	0.32	0.81	0.46	0.96	0.31	0.78	0.35
32–34	0.55	0.19	0.68	0.75	1.30	0.44	0.81	0.46	1.09	0.35	0.81	0.37
34–36	0.57	0.19	0.63	0.69	1.57	0.53	0.77	0.44	1.05	0.34	0.92	0.41
36–38	0.56	0.19	0.70	0.77	1.36	0.46	0.74	0.42	1.00	0.32	0.72	0.33
38–40	0.53	0.18	0.69	0.76	1.36	0.46	0.70	0.40	0.99	0.32	0.77	0.35
40–42	0.54	0.18	0.70	0.77	1.45	0.49	0.72	0.41	0.98	0.31	0.82	0.37
42–44	0.55	0.19	0.69	0.76	1.55	0.53	0.72	0.41	0.98	0.31	0.90	0.40
44–46	0.69	0.23	0.70	0.77	1.75	0.60	0.84	0.48	1.06	0.34	0.95	0.43
46–48	0.68	0.23	0.72	0.79	1.47	0.50	0.77	0.44	0.44	0.32	0.86	0.39
48–50	0.62	0.21	0.68	0.75	1.36	0.30	0.74	0.42	0.42	0.32	0.72	0.39
Average	0.59	0.20	0.64	0.70	1.18	0.39	0.72	0.41	0.91	0.31	0.78	0.35
Stand Dev	0.04	0.01	0.06	0.07	0.23	0.08	0.05	0.03	0.17	0.03	0.09	0.04

240+239Pu depositional signatures as a viable geochronological tool in the Amazon Basin

Figures & Tables

Figure 1

Figure 2

Sediment accumulation rates (mm year-1) and inventories (mBq cm-2)based on the 210Pb and 239+240Pu sediment dating methods_

Depth profiles of dry bulk density (DBD) (g cm-3) and mass accumulation rates (MAR) (g cm-2year-1) of the six sediment cores (PA2, PA9, PA10, RM, PP, PZC) studied in this work_

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