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The existence of missing geomagnetic reversals has been proposed, with potential for new magnetostratigraphic age controls. We estimate geomagnetic reversal frequency from 0 to 155 Ma using adaptive‐bandwidth kernel density estimation (AKDE) to evaluate data sparseness and to assess how reversal frequency changes when recently identified geomagnetic reversals are incorporated into the geomagnetic polarity time scale (GPTS) data set. AKDE is a two‐stage procedure that uses an initial density estimator based on an initial (pilot) bandwidth. We found that the pilot bandwidth determined using cross‐validation is stable with respect to data set length. The AKDE results obtained based on the cross‐validated pilot bandwidth reveal four troughs after the Cretaceous Normal Superchron, spaced 13.5–15.0 Myr apart and corresponding to relatively long chrons (>0.8 Myr). One trough near 32 Ma becomes less distinct after the four recently identified reversals are added to the data set. This sensitivity suggests that troughs in the frequency curve may indicate missing geomagnetic reversals.

The Ethiopia‐Yemen flood basalts are spatially zoned with progressively lower TiO2 lavas from near the Afar depression toward the margins. The timing and rate of emplacement of low TiO2 (LT) lavas are poorly known compared with the ultra‐high TiO2 (HT2) lavas. We measured two high‐precision 40Ar/39Ar ages of 29.63 ± 0.14 and 30.02 ± 0.22 Ma (2σ) from basalts of the 2‐km‐thick LT lava sequence at the Afar plume head margin. Using our eruption age model constructed from our and previous 40Ar/39Ar ages with the paleomagnetic directions, we estimate that the LT lava eruption continued over Chrons C12r‐C12n‐C11r. The eruption of the plume head margin started earlier than the plume head axis emplacement in C12n. Also, the eruption rate was low at the margin, high at the axis. We estimate that the LT lavas are induced by the edge‐driven convection, the result of a plume‐lithosphere interaction, not a plume head. Plain Language Summary The Ethiopia‐Yemen Flood Basalts are thought to be the expression of a mantle plume erupting millions of km3 of basaltic lava in a geologically short period (1–3 million years [Myr]). Titanium concentrations in the flood basalts are zoned and named HT2, HT1, and LT basalts (from high to low Ti). The eruption timing and rate of the HT2 basalts are constrained with high precision, but those of the LT basalts remain ambiguous. Therefore, we measured two high‐precision 40Ar/39Ar ages from LT basalts in the 2‐km‐thick Lima‐Limo section, which erupted northwest of the Afar area. Based on our eruption age model constructed from 40Ar/39Ar ages and paleomagnetic directions, we estimate that the eruption of the LT basalts started earlier than the HT2 basalts that erupted in Chron C12n and lasted over at most ∼2 Myr. The eruptive rate of the LT basalts in the earliest interval was lower than that of the HT2 basalts. This feature of the eruption may be explained by edge‐driven convection caused by the interaction of a gradient of the lithospheric thickness with the Afar mantle plume. Key Points We obtained two new 40Ar/39Ar ages for the low‐Ti basalt from the Lima‐Limo section of the Ethiopia–Yemen flood basalts Based on our eruptive age model, we correlated the Lima‐Limo section to Chrons C12r to C11r We concluded that the non‐plume low‐Ti basalts erupted before the Afar plume high‐Ti basalts because of the plume–lithosphere interaction

The Kibi Plateau in the active Japanese Islands consists of mainly Permian to Cretaceous rocks that have been deeply weathered into a red soil, comprising a peneplain with U-shaped valley. Systematic geological analyses of the Eocene fluvial deposits revealed the paleo-rivers that existed in the eastern Asian continent and streamed out to the paleo-Pacific Ocean. Each paleo-river is traced in a flow line shape without any significant vertical and horizontal displacement. The Eocene shallow marine sediments in a possible coastal region have no relevant inclination. These geological data strongly suggest that the Kibi Plateau has been a stable-coherent tectonic unit since the Eocene through the opening of the Japan Sea and the associated quick rotation of SW Japan in the Middle Miocene. The Kibi Plateau region with a thick crust over 30 km existed as a stable eastern segment of the Asian continent in the Eocene. The Kibi Plateau tectonic unit drifted to the south without any destruction due to the peripheral successive tectonic events such as the Philippine Sea plate subduction and the reactivation of Median Tectonic Line. No subduction related arc volcanism since the Eocene has also influenced to preserve the stable tectonic unit.

The Ethiopia‐Yemen flood basalts are spatially zoned with progressively lower TiO 2 lavas from near the Afar depression toward the margins. The timing and rate of emplacement of low TiO 2 (LT) lavas are poorly known compared with the ultra‐high TiO 2 (HT2) lavas. We measured two high‐precision 40 Ar/ 39 Ar ages of 29.63 ± 0.14 and 30.02 ± 0.22 Ma (2σ) from basalts of the 2‐km‐thick LT lava sequence at the Afar plume head margin. Using our eruption age model constructed from our and previous 40 Ar/ 39 Ar ages with the paleomagnetic directions, we estimate that the LT lava eruption continued over Chrons C12r‐C12n‐C11r. The eruption of the plume head margin started earlier than the plume head axis emplacement in C12n. Also, the eruption rate was low at the margin, high at the axis. We estimate that the LT lavas are induced by the edge‐driven convection, the result of a plume‐lithosphere interaction, not a plume head. The Ethiopia‐Yemen Flood Basalts are thought to be the expression of a mantle plume erupting millions of km 3 of basaltic lava in a geologically short period (1–3 million years [Myr]). Titanium concentrations in the flood basalts are zoned and named HT2, HT1, and LT basalts (from high to low Ti). The eruption timing and rate of the HT2 basalts are constrained with high precision, but those of the LT basalts remain ambiguous. Therefore, we measured two high‐precision 40 Ar/ 39 Ar ages from LT basalts in the 2‐km‐thick Lima‐Limo section, which erupted northwest of the Afar area. Based on our eruption age model constructed from 40 Ar/ 39 Ar ages and paleomagnetic directions, we estimate that the eruption of the LT basalts started earlier than the HT2 basalts that erupted in Chron C12n and lasted over at most ∼2 Myr. The eruptive rate of the LT basalts in the earliest interval was lower than that of the HT2 basalts. This feature of the eruption may be explained by edge‐driven convection caused by the interaction of a gradient of the lithospheric thickness with the Afar mantle plume. We obtained two new 40 Ar/ 39 Ar ages for the low‐Ti basalt from the Lima‐Limo section of the Ethiopia–Yemen flood basalts Based on our eruptive age model, we correlated the Lima‐Limo section to Chrons C12r to C11r We concluded that the non‐plume low‐Ti basalts erupted before the Afar plume high‐Ti basalts because of the plume–lithosphere interaction