Sedimentation rates and age modeling of Late Quaternary marine sediments with unsupported 230Th

Abstract

230 Th is a radionuclide of the 238 U decay series, characterized by natural abundance in sediments and a half-life of 75,380 years, suitable for direct evaluation of sedimentation rates and sediment ages in a time scale of 700,000 years before the present. 230 Th cycle creates a contrast between supported and unsupported 230 Th in the sedimentary matrix due to the different geochemical behaviors of 230 Th and its parent, 234 U. This study aimed at establishing and validating a mathematical model that evaluates sedimentation rates and age modeling based on 230 Th data retrieved from a sediment core sampled in the southeastern Brazilian continental margin. The validation of the age modeling of this method was made through a statistical comparison between its results and those of benthic foraminifera d 18 O record technique, widely used for sediment dating and determination of sedimentation rates. It was observed that the model of unsupported 230 Th was successful in determining Late Quaternary sedimentation rates and ages in a confidence level of 95 %. It was possible to determine several breaking points in unsupported 230 Th vertical profile, and it was shown that those divides correspond to some major intervals between glacial and interglacial periods when compared with the benthic foraminifera record.

100,000 years climatic cycles recorded on very high-resolution seismic data from the Santos Basin’s upper slope during the last 800 ka

“…All cores were retrieved by Petrobras. KF-18 (Ferreira et al, 2015) corresponds, in fact, to the same location of core GL 854. Cores GL 852 and GL 854 have very detailed plankton biochronology (Toledo et al, 2016), spanning respectively the last 321 ka (MIS 9 to MIS 1) and the last 772 ka (MIS19 to MIS1).…”

>b<Carbonate system and elementary geochemistry>/b<: Paleoceanographic and paleoclimatic implications in the South China Sea along the Late Quaternary

“…The chronology of the first 21 m of Hole U1431D was estimated using an excess 230 Th method described by Ferreira et al (2015). 230 Th (half-life = 75.380 yr) is suitable to assess mean sedimentation rates and core chronology for samples up to 700 ka old (Ferreira et al, 2015), especially in areas rich in Th, which originates from the fluvial discharges from several nearby river basins, and with high sedimentation rates. The technique is based on the fact that newly deposited sediments contain an excess of 230 Th ( 230 Thx), whose activity is not supported by its parent 234 U, which is also present in deposited sediments.…”

“…The activities of the radionuclides of interest ( 230 Th and 234 U) were determined in 16 samples distributed along the first 21 m Hole U1431D at the Laboratory of Inorganic Marine Chemistry (LaQIMar) of the Oceanographic Institute (IOUSP). The analysis was carried out in a high-resolution gamma spectrometer (EG&G ORTEC, model 25190P) following all analytical procedures described by Ferreira et al (2015). The analytical quality control was evaluated with the determination of these nuclides in certified reference materials (IAEA326, and IAEA327) (n = 4), and this determination showed satisfactory precision and accuracy, as neither the mean deviations nor errors exceeded 10%.…”

“…Chronology of the first 23 m of Hole U1432C was obtained using an excess 230Th method described by Ferreira et al (2015). Excess 230 Th ( 230 Thxs) values were used to estimate mean sedimentation rates (ν) (Eq.…”