Early Pleistocene Nishikubo Tephra (NK) newly found in the Sayama Formation of the Kazusa Group, west Kanto Plain, NE Japan

Key Points

• To identify and analyze newly discovered Nishikubo tephra within the Sayama Formation of the Kazusa Group in Japan.
• Investigated sediment samples from the Sayama Formation in the Kazusa Group.
• Characterized tephra using refractive index and chemical composition analysis.
• Studied diatom fossils to infer sedimentation environments.
• Identified Nishikubo tephra within the silty layer of the Sayama Formation.
• Tephra is stratigraphically positioned below Zoshiki tephra and above SGO tephra.
• Estimated deposition age of tephra is between 1.35 and 1.45 million years around MIS 43, 45, 47.