1:45 PM - 3:15 PM
[HQR03-P13] Sedimentary environmental changes since the Pleistocene based on concentrations of organic carbon, nitrogen and sulfur of elemental properties of boring cores in Ise Bay, Central Japan.
Keywords:Ise Bay, boring core, CNS elements, sedimentary environment
Nobi Plain is characterized by tilted to westward and thick deposited layer since Pleistocene formed by the Yoro Fault and the stratigraphic classifications and sedimentary processes have been demonstrated based on many boring core results. On the other hand, the information of sedimentary processes in Ise Bay is less than that of the plain.
To research the active faults, AIST collected two boring cores, GS-IB18-1 with 36 m of core length and GS-IB18-2 with 65 m across the Shirako-Noma fault in Ise Bay off Shirako, Suzuka City. Amano et al (2019) explained that these cores were consisted that sand to silt deposited in a fluvial channel and floodplain in the early Pleistocene to Pliocene, sand to silty sand in a fluvial to shallow marine in the middle Pleistocene, sand to silt in a delta to bay in the Last Interglacial stage, sandy gravel including silt with charcoal fragments in a fluvial in the Last Glacial stage, silt and sand in a bay to shallow marine at Holocene. This study analyzed the grain size, concentrations of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS), and stable isotope ratio of organic carbon (δ13Corg) of these cores and discuss the sedimentary environmental changes in Ise Bay since the Pleistocene.
The TOC and TN concentrations of silt in bays during the Holocene and Last Interglacial periods are relatively high, over 0.10% and 1.0% respectively. The total organic carbon to total nitrogen (C/N) ratios are about 10 and the 13Corg -23 to -22‰. These results indicate that most of organic matter in sediments was originated from marine plankton. On the other hand, the concentrations of TOC and TN in sandy gravel, sand and sandy silt in a fluvial channel to shallow marines are mainly low and show high variabilities. The C/N ratios are 20 to 30 and δ13Corg are -28 to -25‰. These results indicate to increase a contribution of organic matter originating from terrestrial higher plants.
The profiles of TS concentrations show relative higher in silt to sand in a bay to shallow marine and lower in sandy gravel, sand and sandy silt in a fluvial. The TS concentrations of silt during the Holocene and Last Interglacial periods show gradually decreases upward. The TS concentration of sediment indicates the amount of pyrite and become proxies of the influences of seawater and freshwater and the redox condition in the seafloor environment. The higher TS concentrations in a bay to shallow marine and lower in sandy gravel, sand and sandy silt in fluvial suggest variations of the influence of seawater and freshwater. The decreasing trends to upward of TS concentration in the Holocene and Last Interglacial periods suggest that the redox conditions in the seafloor have become a weak due to the increase of sea level rise.
To research the active faults, AIST collected two boring cores, GS-IB18-1 with 36 m of core length and GS-IB18-2 with 65 m across the Shirako-Noma fault in Ise Bay off Shirako, Suzuka City. Amano et al (2019) explained that these cores were consisted that sand to silt deposited in a fluvial channel and floodplain in the early Pleistocene to Pliocene, sand to silty sand in a fluvial to shallow marine in the middle Pleistocene, sand to silt in a delta to bay in the Last Interglacial stage, sandy gravel including silt with charcoal fragments in a fluvial in the Last Glacial stage, silt and sand in a bay to shallow marine at Holocene. This study analyzed the grain size, concentrations of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS), and stable isotope ratio of organic carbon (δ13Corg) of these cores and discuss the sedimentary environmental changes in Ise Bay since the Pleistocene.
The TOC and TN concentrations of silt in bays during the Holocene and Last Interglacial periods are relatively high, over 0.10% and 1.0% respectively. The total organic carbon to total nitrogen (C/N) ratios are about 10 and the 13Corg -23 to -22‰. These results indicate that most of organic matter in sediments was originated from marine plankton. On the other hand, the concentrations of TOC and TN in sandy gravel, sand and sandy silt in a fluvial channel to shallow marines are mainly low and show high variabilities. The C/N ratios are 20 to 30 and δ13Corg are -28 to -25‰. These results indicate to increase a contribution of organic matter originating from terrestrial higher plants.
The profiles of TS concentrations show relative higher in silt to sand in a bay to shallow marine and lower in sandy gravel, sand and sandy silt in a fluvial. The TS concentrations of silt during the Holocene and Last Interglacial periods show gradually decreases upward. The TS concentration of sediment indicates the amount of pyrite and become proxies of the influences of seawater and freshwater and the redox condition in the seafloor environment. The higher TS concentrations in a bay to shallow marine and lower in sandy gravel, sand and sandy silt in fluvial suggest variations of the influence of seawater and freshwater. The decreasing trends to upward of TS concentration in the Holocene and Last Interglacial periods suggest that the redox conditions in the seafloor have become a weak due to the increase of sea level rise.