5:15 PM - 6:45 PM
[MIS12-P20] Detection and significance of the alkenone from middle part of Omma Formation in early Pleistocene
Keywords:Omma Formation, alkenone, glacial-eustacy, early Pleistocene
Middle part of the Omma Formation (Early Pleistocene), which extends from Kanazawa City, Ishikawa Prefecture to Oyabe City, Toyama Prefecture, is a shallow marine sequence that records glacial sea-level changes. The glacial-interglacial cycles of 41,000 years, which is characteristic of the Early Pleistocene, has been clearly recorded as sedimentary structures, lithology and molluscan assemblages. The middle part the formation consists of 11 depositional sequences representing glacial-interglacial cycles, and have been actively studied as important clues to understanding the marine environment of the southern edge of the Japan Sea during the Early Pleistocene.
This study applied alkenone paleothermometry, which is widely applied for Quaternary marine offshore sediments, to the middle part of the Omma Formation and discuss paleo-SST fluctuation as well as about alkenone producers through the interval . Samples were collected from the outcrop of the Omma Formation along the Saigawa River. 10 of the 11 sedimentary sequences described by the previous studies can be recognized, and molluscan fossils and lithofacies can be clearly observed. GC (gas chromatography) and GC/MS (gas chromatography-mass spectrometry) analyses allowed us to quantify and identify the organic molecules based on their retention times and mass spectral characteristics. The results indicated that the SST ranged within 23-26℃, and likely records alkenones derived from haptophytes of genus Gephyrocapsa, based on alkenone abundance ratios. The results are also concordant with the changes in composition of the molluscan fauna published in the previous studies. Further studies on alkenone paleo-SST for entire interval of middle part of the Omma formation is required to discuss the paleoenvoronmental changes along the southern edge of the Japan Sea during Early Pleistocene.
This study applied alkenone paleothermometry, which is widely applied for Quaternary marine offshore sediments, to the middle part of the Omma Formation and discuss paleo-SST fluctuation as well as about alkenone producers through the interval . Samples were collected from the outcrop of the Omma Formation along the Saigawa River. 10 of the 11 sedimentary sequences described by the previous studies can be recognized, and molluscan fossils and lithofacies can be clearly observed. GC (gas chromatography) and GC/MS (gas chromatography-mass spectrometry) analyses allowed us to quantify and identify the organic molecules based on their retention times and mass spectral characteristics. The results indicated that the SST ranged within 23-26℃, and likely records alkenones derived from haptophytes of genus Gephyrocapsa, based on alkenone abundance ratios. The results are also concordant with the changes in composition of the molluscan fauna published in the previous studies. Further studies on alkenone paleo-SST for entire interval of middle part of the Omma formation is required to discuss the paleoenvoronmental changes along the southern edge of the Japan Sea during Early Pleistocene.