イノセラムス化石帯区分は上部白亜系の年代層序決定の手法として重要であるが,近年,本邦蝦夷層群において微化石との間に指標する年代区分に不一致が指摘されている.本論はイノセラムス化石帯に対応する炭素同位体比曲線を報告する.北海道大夕張・古丹別両地域のTuronian中部～Santonianの炭素同位体比曲線はInoceramus hobetsensis帯では負方向へのシフトを見せ,I. hobetsensis帯上部及びInoceramus teshioensis帯で特定傾向を示さず安定する.その上位のI. uwajimensis帯からInoceramus amakusensis帯に向かって次第に正方向にシフトする.この炭素同位体比曲線の経時変化パターンは,英国におけるTuronian中部からSantonian下部のものと類似する.それらに加え,I. hobetsensis帯に小規模なピークも見られ,これは国際対比の鍵になる可能性がある.

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北海道北西部古丹別地域における白亜系は下位より中部蝦夷層群の滝見橋層(礫岩とシルト岩), 天狩峠層(砂岩とシルト岩), 白地層(砂岩シルト岩互層からなり上方粗粒化を示す), 上部蝦夷層群の中部羽幌川層(砂岩を挟在するシルト岩), 上部羽幌川層(砂質シルト岩から砂岩への3回の上方粗粒化ユニット)に区分され, その上位を第三系が不整合で覆っている.得られた軟体動物化石群集から, 白地層上部がセノマニアン-チューロニアン階境界に, 中部羽幌川層下部がチューロニアン-コニアシアン階境界に, 中部羽幌川層中部がコニアシアン-サントニアン階境界に, 上部羽幌川層中部～上部がサントニアン-カンパニアン階境界にそれぞれ対比される.

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Based on the stratigraphic investigations of the selected areas of Hokkaido (Fig.1), the successive occurrences of the following ten species of Mytiloides in the mid-Upper Cretaceous sequence have been clarified. The geological ages are determined by the associated ammonites and other well-known species of Inoceramus. They are here abbreviated as UC=Upper Cenomanian, LT, MT and UT=Lower, Middle and Upper Turonian, although the substages are defined tentatively. As to the definition of a species, we depend on current views of authors. In case of an unsettled taxon, we define the species on a number of specimens, admitting a considerably wide range of variation. (1) M. mikasaensis Matsumoto & Noda : UC Zone of Euomphaloceras septemseriatum; (2) M. cf. sackensis (Keller) : low LT; (3) M. columbianus (Heinz) : LT Zone of Pseudaspidoceras flexuosum; (4) M. goppelnensis (Badillet & Sornay) : LT (between 3 and 5); (5) M. mytiloides (Mantell) : mid-LT zone with Mammites sp.; (6) M. labiatus (Schlotheim) : upper LT (maybe lower or higher than 7); (7) M. subhercynicus (Seitz) : high LT; (8) M. hercynicus (Petrascheck) : isolated (highest LT or low MT); (9) M. teraokai (Matsumoto & Noda) : upper MT, Zone of Inoceramus hobetsensis, so far in Southwest Japan; (10) M. incertus (Jimbo) : UT Zone of Subprionocyclus neptuni-I. teshioensis. Some of the above species, e.g. (2), (6) and (8), are rare in the available material and need further hunting. (1) and (9) are so far endemic and should be globally searched for. However, the biostratigraphic succession of the Mytiloides species in our province is generally well correlated with that in the United States. Evolutionary and ecological problems are left for further studies.

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The patterns of geographic distribution and morphological variation of three species of ninespine sticklebacks (Pungitius tymensis, P.pungitius and P.sinensis) in Hokkaido, Japan, were investigated.The range of geographic distribution of P.tymensis was essentially restricted to thefollowing three areas, Teshio District of the northern part of Hokkaido, Ishikari District of thecentral part of Hokkaido and Kushiro-Nemuro District of the eastern part of Hokkaido.Onthe other hand, P.pungitius and P.sinensis were distributed more widely and continuously onHokkaido, compared with the distribution of P.tymensis.P.pungitius was distributed continuouslyin the rivers of the Pacific slope from Nemuro District to Iburi District of the central part ofHokkaido, though, discontinuously in the rivers along the Japan Sea and the Okhotsk Sea slopes.In most rivers facing the Nemuro Straits, P.pungitius was not collected.P.sinensis was distributedin only a few rivers of the Pacific slope from Tokachi District to the Oshima Peninsula ofthe southern part of Hokkaido, but was continuously distributed in the rivers facing the TsugaruStraits, the Okhotsk Sea and the Nemuro Straits.
In three rivers examined (Osatsu, Fukunaga and Bettoga) P.tymensis exninntea more of anupstream distribution than did P.pungitius and/or P.sinensis.In two rivers (Fukunaga andBettoga), P.pungitius and P.sinensis did not occur together along the lengths of the river, butwere distributed with a different range respectively.The morphological characteristics of P.tymensis were quite different from the other two species and its meristic characters varied less thanthose of P.pungitius and P.sinensis.Difference in morphology between P.pungitius and P.sinensis was not significant except for number of lateral plates.The number of vertebrae, in bothP.pungitius and P.sinensis decreased gradually from north to south on the Japan Sea slope, thoughthe other meristic characters did not indicate such a geo-cline.The patterns of geographic variationswere most similar between the two species in the rivers of the Japan Sea slope.
Comparison of morphological characteristics and distribution patterns suggest that P.tymensisis distinguished as an independent species from P.pungitius and P.sinensis.Although thecomparative study does not necessarily show that P.pungitius and P.sinensis are different speciesfrom each other, it does not show that they are completely identical.The latter two species showdifferent distribution patterns in the coexisting rivers and are distributed contiguously and allopatricalyin Hokkaido.It is supposed, therefore, that P.pungitius and P.sinensis in Hokkaidoshould be distinguished from each other at a lower taxonomic level than species.

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Tenkari coal-field coveres the junctional area of three counties, Uryu, Tomamae and Embetsu, and consists of the Neogene Tertiary coal-or lignite-bearing formations overlying the Cretaceous basement. Several oil indicating localities have hitherto been reported from the coal-field by several geologists. The writers newly added several localities and from which obtained oil samples for study.
As has been carried on the chemical analysis of those samples, the following facts were recognized.
(1) The oil-sand from the Cretaceous containes too small quantity of crude oil for quantitative analysis.
(2) The crude nature of the sample obtained from the seepage in the Quaternary of the Kamisekiyuzawa area [Loc. No. 1 in fig. 1] is quite different from that of one from the Tertiary formation of the Sanjussenzawa area [Loc. No. 6 in fig. 1]. As comparing with data of the nature of Japanese crude oil already known, the former belongs to the older type or the Cretaceous-Palaeogene oil type and the latter to the younger or the Neogene oil type [figs. 2-5].
Judging from the subserface geological data to the former seepage, it seems to the writers to be possible that this seepage is fed with crude oil generated in the underneath Cretaceous deposits through the conceald fault.

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北海道北西部羽幌川上流域に分布する上部白亜系に関して,岩相上,下位より中部蝦夷層群天狩峠層,羽幌岳層,白地層,上部蝦夷層群下部羽幌川層,上部羽幌川層,および流矢層の6累層を認識したことに加えて,羽幌岳層以上を計11岩相ユニットに細分し,周辺地域の岩相層序区分との統一化を画つた.この区分に基づいて,大型化石の産出状況を検討したところ,化石帯区分に用いられるイノセラムス,年代対比が可能なアンモナイト類ともに周辺地域における従来の知見と矛盾がない.さらに,他のいくつかのアンモナイトについては,従来考えられてきたよりも層序的分布が限られていることが示唆された.

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The author applied the granulometric and morphoscopic analysis to the samples of beach sand collected at 26 localities with intervals of about 2 km on the “estran” along the Rumoi coast. The results of these experiments, shown in figures 3 to 5, are summarized as follows:
Generally, the beach sands are concentrated in medium grades in composition of grain size, and the median diameters (Md∅) are 1.0 to 2.0 in ∅ scale, so the mean gradient on the estran retains a very gentle slope of 4 to 8 degrees. Unlike fluvial sands, they have a high sorting index (Pd∅) of 0.61 on the average. Judging from these facts, it seems that the distribution of beach sands is commonly controlled by the sieving action of breakers.
The roundness of beach sands is 0.36 on the average in medium size, tends to the intermediate grade between river and dune sands. At any rate, the classification of the four types of quartz grains based on the Cailleux's method, points out the marine origin of EL type more than 30% in contents, yet RM grains originated from dune and beach-dune ridge are simultaneously contained in the beach sands.

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堆積岩中の有機物、特に有機質微化石の色は、堆積岩の熟成度により変化する。これを利用した熟成度指標として、有機質微化石の色の変化を目視によって評価する指標Thermal Alteration Index (TAI; [1]) や、有機質微化石の明度を定量的に評価する指標 Palynomorph Darkness Index (PDI; [2]) が開発され、応用されてきた。有機質微化石の色や明度は、熟成度のほか微化石の壁の厚みや組成、構造により変化することが知られており、熟成度指標として利用する際には、同系統かつ膜の厚みが同程度で装飾の少ない微化石を選んで分析を行い、試料間の比較に用いることとされる。すなわち、同一の堆積岩試料中に見られる微化石の色や明度の多様性には、有機質微化石の膜構造や組成、有機質微化石が被った続成変化の違いなどの多様な情報が反映されている可能性がある。そこで、本研究では、花粉・胞子化石の色から熱熟成度以外の古生物学的・地質学的情報を抽出することを目的に、熱熟成度が同等の堆積岩試料中の花粉・胞子化石の明度および色相を定量的に比較し、それらの関係から、色の変化の要因を考察した。Takashima et al. (2019)[3] で採取された北海道苫前地域

沿いに分布する上部白亜系蝦夷層群羽幌川層の Coniacian 期の泥岩から酸処理・アルカリ処理によって花粉・胞子化石を分離し、花粉・胞子化石を鑑定した。花粉・胞子化石の画像の取得と花粉・胞子壁の厚さの測定には、オリンパス生物顕微鏡CX-43、顕微鏡用カメラBig Eye KP10000および撮影ソフトRisingViewを用い、取得した花粉・胞子化石の画像のうち、花粉・胞子壁の折れ込みなどがない部分を選び、Digital Color Meter (Apple Inc.) により色情報（RGB値）を取得した。RGB値をもとに、有機質微化石の明度を示すPDIと、明度と独立した色情報として色相 (hue) を算出し、花粉・胞子粒子のそれぞれの値を比較した。PDIと色相の間にはよい相関が見られ (R² = 0.8768, n = 31)、明度が高い (PDIが低い) 花粉・胞子化石ほど黄色に、明度が低い (PDIが高い) 花粉・胞子化石ほど赤色に近づく関係が示された。さらに、花粉と胞子の比較では、花粉化石は明るく黄色い領域（低PDI、高hue）に、胞子化石は暗く赤い領域（高PDI、低hue）に分布する傾向を示した。熱熟成度が同等の堆積岩中の花粉・胞子化石にPDIおよびhueの違いをもたらす要因として、1) 形態（花粉・胞子壁の厚さ)の違い、2) 続成過程の違い、3) 花粉・胞子壁を構成する成分の違いが考えられる。1) に関して、花粉・胞子壁の厚みが増すほど暗く赤くなる弱い傾向 (thickness vs PDI: R² = 0.28, thickness vs hue, R² =0.22) が認められるものの、花粉や胞子のPDIとhueの大幅な差異は厚みの違いのみで説明することはできない。2) に関して、風媒の花粉は飛散により堆積場近傍まで運搬され得る一方で、胞子は主に流水により運搬され、蝦夷層群の堆積場に到達するまでにより重度の初期続成作用を被った可能性があり、これが胞子化石のPDIが高く赤い色相を示す要因となった可能性がある。ただし、胞子同様の運搬経路を経た花粉が存在しないとは考えにくく、現時点での予察データにおいて暗く赤い色相を示す花粉化石がないことが説明できない。3) については、花粉・胞子壁を構成するスポロポレニンの成分が花粉と胞子で系統的に異なることが報告されており [4]、この差異が熱熟成や初期続成作用を受けた際のPDI・色相の変化の程度に違いを生じさせている可能性が考えられる。[1]Staplin, F.L., 1969. Bull. Can. Pet. Geol., 17 47–66.[2]Goodhue, R. and Clayton, G., 2010, Palynology, 34 (2) 147–156[3]Takashima, R. et al., 2019, Newsl. Stratigr., 52 (3) 341-376[4]Xue, J. et al., 2020, Mol. Plant., 13 (11) 1644-1653

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Biostratinomic processes, which include sedimentologic processes such as fragmentation, re-orientation, size-sorting, disarticulation and abrasion, are easily read from the evidence of fossil records. The formation of shell-concentration (Inoceramus uwajimensis bed) in the black mudstone of the Upper Yezo Group in the study area was controlled by the following three factors : (1) physical control such as resedimentation by bottom current and shell-accumulation by winnowing of fine sediments, (2) ecological factors, and (3) paleoenvironmental factor concerning the dissolved oxygen level which can be reconstructed from trace fossil assemblage. Concentrations of inoceramid shells are common and remarkable features in the monotonous Upper Cretaceous mudstone of the study area. Five types of shell beds, namely Type 1 to Type 5, are distinguished on the basis of the mode of occurrence. Most of the shell beds are discontinuous and fade away laterally. The shell beds of Types 1 and 2 consist of articulate and less abraded shells with the left-valve down, which suggests these two shell beds consist of autochthonous shells and the life positions are preserved. "Clump-like" modes of occurrence can be observed in Type 3, but the shells were not in life position as a result of subtle in situ reworking. Shell-size is totally even in such clumps. This suggests that they formed a colony which consists of individuals of the same generation as seen in recent Mytilus colonies. Type 4 usually consists of graded shell fragments and less broken shells of convex-down position at the bottom of shell beds. Type 4 undoubtedly represents an allochthonous mode of occurrence. Type 5 contains mixed fauna which consists of epifaunal and infaunal bivalves, benthic heteromorph ammonites, planktonic ammonites and planktonic foraminifera. In spite of the intense reworking, it suggests very rapid deposition after the storm that mixed faunas of different modes of life preserved very well. The assemblage of all the shell beds except for type 5 shows very low diversity : dominant I. uwajimensis plus a few other bivalves and/or gastropods. Trace fossil assemblages in the ambient black mudstone indicate an oxygen-deficient condition. One reason why I. uwajimensis shows a monotypic composition may be due to some ecological factors. I. uwajimensis seems to have adapted to such oxygen-poor environments below the intense storm-wave base where was hard for most of the other animals to live.

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