240+239 Pu depositional signatures as a viable geochronological tool in the Amazon BasinPublié en ligne: 02 juin 2017 Pages: 142 - 149 Reçu: 01 janv. 2017 Accepté: 21 avr. 2017 © 2017 L. M. Sanders. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.
Figure 1 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. Figure 2 239+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. Study Site 210 Pb (mm year-1 )210 Pb Bq cm-2 239+240 Pu (mm year-1 )239+240 Pu (mBq cm-2 )Major River 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 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