5:15 PM - 6:45 PM
[MIS05-P06] Environmental changes during the Holocene based on element properties measured by XRF core scanner off the mouth of Kinokawa River in Kiisuido Strait, Southwest Japan.
Keywords:XRF core scanner, Kiisuidou Strait, Holocene, sea level change, anthoropogenic impact
The Kiisuido Strait is located between Tokushima and Wakayama Prefectures and is connected to the Seto Inland Sea and the Pacific Ocean. The environment of the Kiisuido Strait is influenced by the inflow of Kuroshio water from the Pacific Ocean and the supply from the land. The Kii Channel is shallower than 60 m and was land during the last glacial period. To demonstrate the environmental changes of the Kiisuido Strait during the Holocene, this study collected core sediment (core length 346 cm) offshore of the mouth of the Kinokawa River, Wakayama Prefecture, used by gravity corer in December 2021. The collected core was measured X ray CT image and then split in half. The split core was measured color and subsampled at 2.3 cm interval. These subsampled were used for grain size by laser diffraction particle size analyze (LA960, Shimadzu) and 210Pb and 137Cs dating. Shell fossiles from the subsampled were used for accelerator mass spectrometry radiocarbon dating (14C dating). The other split core was measured the elements by XRF core scanner. The measurement was 30kV, 55mA and 10 seconds of exposure times using Molybdenum X-ray tubes at 2 mm intervals, respectively. All the XRF spectra were reevaluated by the Q-Spec software (version 15.1) to obtain individual element counts. The element counts were normalized by the method of centered log-ratio(clr, Weltje and Tjallingii, 2008).
The collected core showed fining to upward lithological succession and mainly three sections. The lower section at the core depth of 320-346 cm was composited by poorly sorted fine sand with shell fragments, middle section at 119-320 cm depth by silty sand-sandy silt with shell and wood fragments, and upper section above 119 cm depth by silt. Age model estimated by 14C dating indicated 8.2-11.0 cal kyr BP in the lower section, 0.5-8.2 cal kyr BP in the middle and <0.5 cal kyr BP in the upper. The depositional age in the upper section estimated by 210Pb and 137Cs was harmonic with 14C dating result. The clr values of Si, K Ti decreased toward the middle section from the lower, meanwhile Br increased. These variations suggested that sand grain decreased and organic matter increased by sedimentary environment changes with sea level. Profiles of Cu and Zn showed the increasing toward the core surface in the upper section. These increasing trends suggested the anthropogenic impact in 20th century.
References: Weltje and Tjallingii (2008) Calibration of XRF core scanners for quantitative geochemical logging of sediment cores: Theory and application. Earth and Planetary Science Letters, 274, 423–438
The collected core showed fining to upward lithological succession and mainly three sections. The lower section at the core depth of 320-346 cm was composited by poorly sorted fine sand with shell fragments, middle section at 119-320 cm depth by silty sand-sandy silt with shell and wood fragments, and upper section above 119 cm depth by silt. Age model estimated by 14C dating indicated 8.2-11.0 cal kyr BP in the lower section, 0.5-8.2 cal kyr BP in the middle and <0.5 cal kyr BP in the upper. The depositional age in the upper section estimated by 210Pb and 137Cs was harmonic with 14C dating result. The clr values of Si, K Ti decreased toward the middle section from the lower, meanwhile Br increased. These variations suggested that sand grain decreased and organic matter increased by sedimentary environment changes with sea level. Profiles of Cu and Zn showed the increasing toward the core surface in the upper section. These increasing trends suggested the anthropogenic impact in 20th century.
References: Weltje and Tjallingii (2008) Calibration of XRF core scanners for quantitative geochemical logging of sediment cores: Theory and application. Earth and Planetary Science Letters, 274, 423–438