A record of the upper Olduvai geomagnetic polarity transition from a sediment core in southern Yokohama City, Pacific side of central Japan

Abstract

A detailed paleomagnetic record of the upper Olduvai polarity transition was obtained from a 106.72 m-long sediment core drilled in southern Yokohama City, located on the northern Miura Peninsula, on the Pacific side of central Japan. The core spans the upper part of the Nojima Formation and the lowermost part of the Ofuna Formation, both of which correspond to the middle Kazusa Group (Lower Pleistocene forearc basin fill). The record was reconstructed using discrete specimens taken throughout mudstone and/or sandy mudstone sequences in the Nojima Formation. In this record, the virtual geomagnetic pole (VGP) fluctuation accompanying the polarity transition was determined to occur between depths of 66.99 and 63.60 m. These depths have been dated at 1784.4 and 1779.9 ka, respectively, and the duration of the polarity transition is estimated to be 4.5 kyr using an age model based on a δ 18 O record from that core. The VGP paths during the transition do not appear to show any preferred longitudinal bands. However, the VGP positions cluster in five areas: (A) eastern Asia near Japan, (B) the Middle East, (C) eastern North America (North Atlantic), (D) off southern Australasia, and (E) the southern South Atlantic off South Africa. The primary locations of the observed VGP clusters coincide with the areas on the Earth's surface that possess a strong downward flux of the vertical component of the present geomagnetic non-axial dipole field. The relative paleointensity rapidly decreased approximately 1 kyr before the beginning of the polarity transition and gradually recovered to its initial level in 12 kyr.

Strengthening Atlantic Inflow Across the Mid‐Pleistocene Transition

“…It has been suggested (Huber et al., 2000) that N. pachyderma only became fully polar affiliated at around 1.1 Ma (being only subpolar up until that time), which would imply that faunal‐based records from older periods might be less reliable in terms of temperature reconstruction. On the other hand, the presence of N. pachyderma in the central Arctic around the time of the Olduvai geomagnetic event (Atkins, 1991) (dated to around 1.8 Ma [Kusu et al., 2016]) implies that the species was already adapted to polar conditions well before the MPT. This agrees with earlier estimates for the cold water adaption of N. pachyderma around 1.7 Ma (Raymo et al., 1987).…”

Revisión de datos paleomagnéticos de flujos de lava asociados al Campo Volcánico Michoacán Guanajuato: implicaciones sobre el comportamiento del campo magnético terrestre durante el Plio-Cuaternario

“…Encontraron flujos con polaridad intermedia fechados en 1.92 Ma superpuestos por un flujo de polaridad normal de 1.85 Ma. Kusu et al (2016) obtuvieron un registro paleomagnético casi continuo de una inversión de polaridad del Alto Olduvai de un núcleo sedimentario de Yokohama, Japón. La transición de polaridad se determinó entre 1.78-1.77 Ma, observando una secuencia de polaridades N-I-N.…”

Geology and fossil cold-seep assemblages in the Kazusa Group on the northern Miura Peninsula, central Japan

“…Fig.5. Geologic columns, nannofossil datums, oxygen isotope fluctuations of planktonic foraminifera, and relative abundance of Kuroshio-type planktonic foraminifers derived from cores E, J and I. Geologic columns, nannofossil data and foraminiferal data of cores J and E are based onNozaki et al, 2014 and geologic column, foraminiferal data and magnetic polarlity of core I are onKusu et al (2014Kusu et al ( , 2016, respectively. Correlations with the LR04 stack model(Lisiecki and Raymo 2005) on the basis of interpreted MISs are also shown.…”

“…では大船層下部から野島層上部にかけて狭在する 凝灰岩鍵層 NOT-1 から NOT-12(Nozaki et al, 2014) が 観察される．そのうち，Traverse 41，45 には穂高 -Kd39 テフラに対比された NOT-1 の Kb33) が確認できるが，これらは それぞれ黄和田層中の Kd25 (大峰 -SK110; 長橋ほか, 2000) お よ び Kd24 ( 白 沢 天 狗 -SK100; Satoguchiand Nagahashi, 2012) に対比された (藤岡ほか, 2003) ． 本地域の野島層から小柴層の年代は，石灰質ナノ化石，古 地磁気，浮遊性有孔虫の酸素同位体比によって検討されてき た (Fig.5：藤岡ほか, 2003; 楠 ほか, 2014; Nozaki et al, 2014; Kusu et al, 2016) ．石灰質ナノ化石の解析によると， 大船層の中位には，佐藤ほか (1999) の石灰質ナノ化石基準 面 12 が，大船層上部から小柴層最下部の砂質泥岩層にかけ ての層準に基準面 11 が，小柴層下部の泥質砂岩中に基準面 10 が，それぞれ見いだされている (藤岡ほか, 2003; Nozaki et al, 2014) ．古地磁気層序についてみると， 「瀬上市民の 森」 と 「氷取沢市民の森」 を分ける尾根部から掘削されたボー リングコア I で，大船層下部にオルドバイ正磁極亜帯の上限 が確認された (楠ほか, 2014, Kusu et al, 2016)．さらに， Nozaki et al, 2014;Kusu et al, 2016) ．この MIS の認定 に基づき構築された年代モデルから，野島層上部から小柴層 下部にかけての 24 枚の凝灰岩層について，堆積年代が与え られている (Table 1; Nozaki et al, 2014) ．…”