A Rapid Test for Tephra Layer Determination in Marine Core Sediment: Case of SO189/2_04KL in Bengkulu Basin, Indonesia

Volcanic ash is a high-potential, widespread volcanic product that is commonly used as a marker in geology and archeology. It can be found in marine sediment up to a thousand kilometers from its source (e.g., the Young Tuff Toba). The presence of a volcanic layer in marine sediment is critical for understanding Earth's processes. Here, we test amethod to determine the tephra layer in a marine sediment core. It is SO189/2_04KL from western Sumatra water, specifically in Bengkulu Basin, Indonesia. Using an X-Ray Fluorescence (XRF) handheld, chemical composition wasobtained only in the interval 600–800 cm below the seafloor (cmbsf). The visible volcanoclastic unit (VVU) is calculated using three elemental ratios: In (Fe/Ca), In (Mn/Ca), and (Fe+Mn)/(Ca+Sr). We also used In (Rb/Sr) and In (Zr/Rb) to differentiate between primary and secondary VVUs. This study found three tephra layers (two VVUp on the intervals of 661- 664 cmbsf and 739–742 cmbsf, and one secondary VVUs layer on the interval of 748–750 cmbsf. We conclude that the elemental ratios In (Fe/Mn), InMn/Ca, and (Fe+Mn)/(Sr+Ca) could be used to determine the VVU layer, whereas In (Rb/Sr) and In (Zr/Rb) could be used to differentiate primary andsecondary VVU layers..