10:45 〜 11:00
[SCG57-01] U–Pb Dating of Biogenic Apatite in Pelagic Clay: A New Approach for Deep-Sea Sediment Chronology
キーワード：遠洋性粘土、生物源アパタイト、ウラン鉛年代決定、LA-ICP-MS
Pelagic clay is one of the most widespread deep-sea sediment types, covering approximately 38% of the ocean floor. It is primarily deposited in the deepest and most remote areas of the ocean. Recently, pelagic clay has garnered significant attention due to its high concentrations of rare-earth elements [1] and its potential to record unique geological events, such as previously unrecognized meteorite impacts [2]. However, the precise age determination of pelagic clay remains challenging due to the absence of typical index fossils (e.g., foraminifera or radiolarians), thereby limiting high-resolution paleoceanographic studies.
In this study, we propose U–Pb dating of biogenic apatite (e.g., fish teeth, bones, and denticles) extracted from pelagic clay as a potential method for age determination. Apatite incorporates common Pb, which complicates U–Pb dating and limits precision compared to zircon, but its ability to retain trace elements and its closure temperature of ~375–600°C make it valuable for geochronology and tracking geochemical processes. Biogenic apatite is a common constituent of pelagic clay; thus, if its age can be accurately determined, it may provide a reliable estimate of the sedimentation age of the host pelagic clay.
To evaluate this method, U–Pb dating method is applied to biogenic apatite extracted from pelagic clay samples obtained from Deep Sea Drilling Project (DSDP) Hole 576B, Ocean Drilling Program (ODP) Hole 886C, and Integrated Ocean Drilling Program (IODP) Holes U1365A and U1370D. These cores contain stratigraphic intervals that likely date back to the Cretaceous period, as indicated by carbonate layers dated to approximately 64–65 Ma or Ir-enriched layers that likely represent the Cretaceous-Paleogene (K/Pg) boundary [3]. Therefore, using these samples, it is possible to evaluate whether U–Pb dating can effectively determine the sedimentation chronology of pelagic clay.
The clay samples were sieved, and biogenic apatite grains were manually selected under a binocular microscope. The selected grains were embedded in resin and polished to a 1 µm finish. Their trace element distributions were mapped using excimer laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Afterwards, U–Pb isotope analyses were conducted using femtosecond laser ablation multiple collector-inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS).
In this presentation, we will discuss the feasibility of the present technique for U–Pb dating on biogenic apatite in pelagic clay as a principal tool for accurate age determination of pelagic clay.
[1] Kato et al. (2011) Nature Geosci. 4, 535–539. [2] Nozaki et al. (2019) Sci. Rep. 9, 16111. [3] Alvarez Zarikian, (2015) Palaeogeogr. Palaeoclimatol. Palaeoecol. 419, 115-142.
In this study, we propose U–Pb dating of biogenic apatite (e.g., fish teeth, bones, and denticles) extracted from pelagic clay as a potential method for age determination. Apatite incorporates common Pb, which complicates U–Pb dating and limits precision compared to zircon, but its ability to retain trace elements and its closure temperature of ~375–600°C make it valuable for geochronology and tracking geochemical processes. Biogenic apatite is a common constituent of pelagic clay; thus, if its age can be accurately determined, it may provide a reliable estimate of the sedimentation age of the host pelagic clay.
To evaluate this method, U–Pb dating method is applied to biogenic apatite extracted from pelagic clay samples obtained from Deep Sea Drilling Project (DSDP) Hole 576B, Ocean Drilling Program (ODP) Hole 886C, and Integrated Ocean Drilling Program (IODP) Holes U1365A and U1370D. These cores contain stratigraphic intervals that likely date back to the Cretaceous period, as indicated by carbonate layers dated to approximately 64–65 Ma or Ir-enriched layers that likely represent the Cretaceous-Paleogene (K/Pg) boundary [3]. Therefore, using these samples, it is possible to evaluate whether U–Pb dating can effectively determine the sedimentation chronology of pelagic clay.
The clay samples were sieved, and biogenic apatite grains were manually selected under a binocular microscope. The selected grains were embedded in resin and polished to a 1 µm finish. Their trace element distributions were mapped using excimer laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Afterwards, U–Pb isotope analyses were conducted using femtosecond laser ablation multiple collector-inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS).
In this presentation, we will discuss the feasibility of the present technique for U–Pb dating on biogenic apatite in pelagic clay as a principal tool for accurate age determination of pelagic clay.
[1] Kato et al. (2011) Nature Geosci. 4, 535–539. [2] Nozaki et al. (2019) Sci. Rep. 9, 16111. [3] Alvarez Zarikian, (2015) Palaeogeogr. Palaeoclimatol. Palaeoecol. 419, 115-142.