Tabulate Corals from the Lower Devonian Ohno Formation in the Hikoroichi area, Iwate Prefecture, Northeast Japan

A nearly complete shell of the genus Adocus (Adocidae; Pan-Trionychia; Cryptodira; Testudines) was collected from the late Cretaceous (Turonian) Tamagawa Formation of Kuji Group at Kuji City, Iwate Prefecture, northeast Japan. This turtle shows unique features such as the loss of cervical scute, extreme expansion of marginal scutes overlying costal plates, and exclusion of the humeral- pectoral sulcus from entoplastron. Thus, A. kohaku is erected as a new species. As A. kohaku shows most derived position of A. kohaku within this genus, morphological diversity of the genus Adocus seems to have occurred rather early in its evolution in Eastern Asia.

It is well known that a counterclockwise rotation occurred in the Miocene in northeast Japan. However, the detailed timing and mechanism of the rotation has been debated. Moreover, there has been no research about the relationship between rotational tectonics and the evolution of sedimentary basins. We carried out paleomagnetic and rock magnetic analyses in Nishiwaga Town, Iwate Prefecture, northeast Japan, where the stratigraphy and sedimentary basin formation have previously been clarified. We found that there was a counterclockwise rotational movement of about 45° at about 15 Ma. From our results and previous studies on the tectonics and sedimentary basin development, we are able to ascertain the following tectonic history and sedimentary basin evolution in this area: (i) before the rotational movement, sandstone and mudstone were deposited in a tranquil environment with no volcanic activity coupled with slow tectonic subsidence; (ii) between 16.4–15.1 Ma and 14 Ma, a counterclockwise rotation occurred with rapid tectonic subsidence and continuous explosive volcanism; (iii) at about 14 Ma, the counterclockwise rotation ended and there was a reduction in both subsidence and volcanism. This result shows the impact that rotational tectonics can have on sedimentary basin formation.

A fragmentary femur of the Rhinocerotidae (Perissodactyla, Mammalia) from the lower Miocene Yotsuyaku Formation of the Shiratorigawa Group, Ichinohe, Iwate Prefecture, Northeast Japan is redescribed, and the fossil record of Japanese early Miocene rhinocerotids, including footprints, is briefly reviewed. The femur is identified as belonging to an indeterminate species of rhinocerotid, cf. Aceritherini, in having the distal portion of the base of the lesser trochanter situated near the apex of the third trochanter and a less projected third trochanter than in most rhinocerotids. Since ca. 20 Ma, rhinocerotids have inhabited and been widely distributed in Japan, which formed an eastern margin of continental East Asia at that time.

Forearc basin deposits on continental margins contain important information that can be used to reconstruct the tectonic setting, volcanism, and climate at the time of their deposition. Coal‐bearing terrestrial to shallow marine strata in Northeast Japan were deposited in a forearc basin along the Eurasian continental margin during the Cretaceous–Paleogene. The rocks exposed in the Kado district, Iwate Prefecture, in the northern Kitakami Mountains include the Upper Cretaceous Yokomichi Formation and the Paleogene Kogawa Group; the latter is known for high‐quality refractory clay (kaolin clay). However, their stratigraphy and sedimentological characteristics are not yet fully understood. To reconstruct the formation and filling of the basin, we investigated field observations, U–Pb dating of tuff samples, XRD analysis of tuff and mudstone samples, and vitrinite reflectance of coal samples in this sequence. The U–Pb ages of the Yokomichi Formation and the Kogawa Group are ∼86 Ma and 58–52 Ma, respectively. The U–Pb age of the kaolin‐dominated tuffaceous rock (“red rocks”) is 56.1 ± 0.2 Ma. The mean random vitrinite reflectance (VRr) ranges from 0.37% to 0.53% through the sequence. We propose the following sequence for the formation and filling of the basin. (1) The basin initially formed during the Coniacian–Santonian (Late Cretaceous) and was filled by fluvial–lacustrine sediment. (2) These sediments kept the shallow burial depths during a ∼28 Myr and made a hiatus (86–58 Ma). (3) The basin was reactivated and covered by tuffs during the Thanetian, and the tuffs were altered to kaolin clay during the Paleocene–Eocene Thermal Maximum. (4) The basin was filled rapidly by alluvial fan deposits and subsided <2300 m (assuming a geothermal gradient of >30 K/km). (5) The basin was uplifted and exhumed at a rate of >50 m/Myr faster than the mean exhumation rate of the Kitakami Mountains since the Paleogene.

The purpose of this paper is to report on the changing social structure and function of the Tochikairyoku (Land Improvement Associations) in Kitakami, Iwate Prefecture, located in North East Japan. This case study was conducted by interviewing executive members of the Iwate Chubu Tochikairyoku and the farming membership working the land and by collecting and examining all available data pertaining to the changes affecting the functioning of this organization. The Tochikairyoku is a non-profit public organization of and for farmers engaged in agriculture or animal husbandry and serves to liaise between farmers and central and local governments. All the costs of management and staff are borne by the members. All decisions to be undertaken must be ratified by the members. The results of the case study indicate that there has been a significant consolidation in the number of Tochikairyoku and farms owing to the dwindling rural population and the ageing of those actively farming the land. Another major factor has been the recent changes in the Japanese Government’s policy that now favours bigger agricultural units over smaller farmers. The Tochikairyoku are instrumental in promoting the new government policies by maintaining irrigation infrastructure and improving the quality of arable land in order to encourage the leasing of land from the smaller farmers to the bigger farm units. The new 2018 Law has effected changes in the election of executive members of the Tochikairyoku to include representatives of agribusiness interests and has introduced a reform of the Tochikairyoku’s accounting practices to make them more transparent.

<p>During the 2011 Tohoku-oki earthquake the pacific coast of northeast Japan experienced significant subsidence, while in the years after it has undergone a continuous phase of uplift during the post-seismic period. The dense geodetic network deployed by GEONET and Tohoku university between 2011 and 2016 have captured variations in surface deformation along the coast, highlighting rapid uplift rates of ~7 cm/year on the Miyagi coast (Muto et al., 2019, Sci.Adv.) and ~3-4 cm/year on the Fukushima and Iwate coasts. Previous studies in the last decade have revealed the post-seismic deformation is due to a combination of both rapid viscoelastic flow and stress-driven afterslip, explaining the post-seismic vertical deformation pattern over northeast Japan as well as unravel its associated rheological complexity (e.g., Agata et al., 2019, Nat. Commun; Freed et al., 2017, EPSL; Hu et al., 2016, JGR; Muto et al., 2019, Sci.Adv.). Furthermore, continuous coastal uplift has had societal consequences, where the piers at the port are no longer suited to conduct many activities, particularly those for the fish industry. The large co-seismic subsidence of coastal areas caused the submersion of port piers, with rapid rebuilding to return the now submerged piers to sea-level. Nevertheless, the continuous uplift in the post-seismic period has now raised these rebuild piers above sea level and necessitates reduction in height back to sea level again (Iinuma, 2018, JDR). In this presentation, we employ forward modeling to improve estimates of future uplift and the time required for full recovery of coastal regions to their pre-event relative sea level.</p><p> </p><p>We present a numerical model using laboratory-derived constitutive laws and compare our modeled displacement with the geodetic observations (Ozawa et al., 2012, JGR; Tomita et al., 2017, Sci.Adv.; Watanabe et al., 2014, GRL). The model is constrained by terrestrial and seafloor geodetic observations in both horizontal and vertical components and incorporates a three-dimensional heterogeneous viscoelastic rheology fully coupled with stress-driven afterslip on the plate interface.</p><p> </p><p>Our model exhibits good agreement with the cumulative displacements, both in magnitude and azimuthal direction. We extend the time-series simulation for a further 20 years and estimate the recovery time to pre-event levels for the GNSS sites along the coastal areas. Our results show a recovery period of ~18 years after the mainshock for Ishinomaki site in Miyagi prefecture, which had the largest coseismic subsidence (up to ~1.2 m). We also estimate a recovery period of ~14-16 years for the coastal areas of Iwate and Fukushima prefectures, which experienced coseismic subsidence of ~0.5 m. The model adds an improvement to the previous estimates (Iinuma, 2018, JDR) by incorporating consideration of the coupling of viscoelastic relaxation and stress-driven afterslip.</p>

岩手県北上市付近の火山灰土壌の生成について Ｉ 地形と土壌生成

Planktonic foraminiferal assemblages from the Miocene sequence in the Ichinoseki area, Iwate Prefecture, Northeast Japan

58 Middle Miocene molluscs from the lower part of the Tomesaki Formation, Aomori and Iwate Prefectures, Northeast Japan : As an example of molluscan fauna after the "Mid-Neogene Climatic Optimum"

Mode of greentuff volcanism in Ou backbone ranges in Nishiwaga town, Iwate prefecture, northeast Japan

1005 Fossil Mollusca of the Lower Miocene Yotsuyaku Formation in the Ninohe district, Iwate Prefecture, Northeast Japan : Part 2 (2). Gastropoda

Terrestrial vertebrates from the Late Cretaceous Tamagawa Formation of the Kuji Group of Kuji, Iwate Prefecture, northeast Japan

Molluscan and plant fossils from ancient mangrove swamps are known from upper Lower to lower Middle Miocene sediments in Southwest Japan. Given that the mangrove-swamp-dwelling bivalve Geloina was recently found in the Tate Sandstone Member of the Kadonosawa Formation in the Ninohe district, northeastern Japan, it was expected that mangrove pollen would also be found at this site. To investigate this possibility, 26 samples were collected from the Tate Sandstone Member at two sites (Tate and Kitadate). The pollen composition at both sites is characteristic of the NP-2 zone of Neogene pollen zones (Yamanoi 1992a). Mangrove pollen (Kandelia sp.) fossils were first found in the uppermost part of the Tate Sandstone Member at the Kitadate site, representing the northernmost record of Miocene fossil mangrove in Japan. Based on present-day mangrove assemblages and distribution, the average wintertime temperature in the Ninohe area at the time represented by the pollen fossils is estimated to have been about 11°C higher than that of today.

Detrital zircon U–Pb ages of sandstone within the Jurassic accretionary complex in the North Kitakami Belt of the Sotoyama District, Iwate Prefecture, Northeast Japan

岩手県宮古市日出島に露出している下部白亜系（アプチアン～アルビアン）宮古層群の日出島層は，主にタービダイト砂岩と泥岩の互層と礫岩層や厚い砂岩層から成り，スランプ層や土石流堆積物を伴う．土石流堆積物からは，保存状態の悪いGlycymerisやEriphyla，Nipponitrigonia，厚歯二枚貝などの二枚貝化石が産出し，これら浅海生の二枚貝化石は典型的な異地性の産状を示す．