Preliminary tephrochronological study of the Yezo Group (uppermost Albian–basal Campanian) in north Japan

Identification of the source caldera for the Middle Miocene ash‐flow tuffs in the Kii Peninsula based on apatite trace‐element composition

“…The trace-element content of apatite is affected by the chemical composition of the host magma and factors that determine the distribution of elements: temperature, oxygen, and halogen fugacities (Sell & Samson, 2011a, 2011b. Consequently, a knowledge of these factors is useful for discriminating and/or correlating tephra from different and/or the same eruption episodes (Kuwabara et al, 2019;Sell et al, 2015;Sell & Samson, 2011a, 2011bTakashima et al, 2020). In addition, multiple caldera-forming eruptions can have the same magma properties.…”

“…Indeed, the identical trace-element compositions in the apatite in the ash-flow tuffs from the Kumano-North and Kumano calderas (Figure 4b, c) could imply that multiple eruptions may have occurred. Additionally, since apatite crystals are relatively resistant to subsequent alteration, such as welding or diagenesis (Kuwabara et al, 2019;Takashima et al, 2017Takashima et al, , 2020, they preserve the trace-element properties at the time of magma eruption. Therefore, the trace-element properties in apatite are well suited for clarifying the origin of the igneous and volcaniclastic rocks in the MFVK, which have similar chemical compositions in terms of bulk major and trace elements; however, it has been proposed that most of these rocks underwent subsequent alteration, partly by the dense welding (Shinjoe et al, 2007(Shinjoe et al, , 2010.…”

“…Apatite is highly resistant to burial diagenesis, welding and weathering processes (Churchman & Lowe, 2012;Morton & Hallsworth, 2007;Takashima et al, 2017), and its trace-element composition is known to change with crystallization in response to various magmatic conditions (Miles et al, 2014;Prowatke & Klemme, 2006). By utilizing such characteristics, several studies on the apatite trace-element compositions of tephras and ash-flow tuffs have been successful in identifying source calderas and in correlating tephra deposits (Kuwabara et al, 2019;Sell & Samson, 2011a, 2011bTakashima et al, 2017Takashima et al, , 2020.…”

The Global Boundary Stratotype Section and Point (GSSP) for the base of the Coniacian Stage (Salzgitter-Salder, Germany) and its auxiliary sections (Słupia Nadbrzeżna, central Poland; Střeleč, Czech Republic; and El Rosario, NE Mexico)

“…In the Ha-1 Unit of the Haborogawa Formation (Turonian-Campanian), the Turonian-Coniacian boundary is placed in the middle of the Navigation CIE, their NP-18 event (as determined by a δ 13 C org curve, reinforced by the appearance of several key biostratigraphic markers) (Takashima et al, 2010(Takashima et al, , 2019. Of particular interest to this report is the presence of a thick tuff, essentially located on the Turonian-Coniacian boundary, which is widely traceable for hundreds of kilometres across Hokkaido (Takashima et al, 2019;Kuwabara et al, 2019). The U-Pb radiometric age of this horizon is 89.94 ± 0.98 Ma -essentially indistinguishable from the consensus age of the Turonian-Coniacian boundary (Kuwabara et al, 2019).…”

“…Of particular interest to this report is the presence of a thick tuff, essentially located on the Turonian-Coniacian boundary, which is widely traceable for hundreds of kilometres across Hokkaido (Takashima et al, 2019;Kuwabara et al, 2019). The U-Pb radiometric age of this horizon is 89.94 ± 0.98 Ma -essentially indistinguishable from the consensus age of the Turonian-Coniacian boundary (Kuwabara et al, 2019). This is a particularly significant result because it suggests the Turonian-Coniacian boundary was accurately placed via chemostratigraphic means (e.g., Takashima et al, 2010Takashima et al, , 2019Hayakawa and Hirano, 2013), which would in turn suggest that the base of the Coniacian should be within the Inoceramus uwajimensis Zone, not at the base of the zone as traditionally interpreted (e.g., Toshimitsu et al, 2007, and references therein; see also below).…”