四国中・東部の前期白亜紀非海生二枚貝動物群

Cretaceous non-marine faunas in Central and Eastern Shikoku can be classified into the Masaki and Sakashu faunal groups on the basis of their taxonomic components and a new stratigraphy and tectonic subdivision of the Chichibu Superbelt. The non-marine bivalves from the Monobegawa Group in the Masaki Belt belong to the Masaki Faunal Group which are identified the Hauterivian Tatsukawa fauna, Late Barremian Yunoki fauna and Early Aptian Hibihara fauna. The non-marine bivalves from the Nankai and Takegatani groups of the Sakashu Belt belong to the Sakashu Faunal Group which are identified the Hauterivian Shobu fauna. The three faunas of the Masaki Faunal Group in Central and East Shikoku are found in stratigraphic order. The Masaki Faunal Group is characterized by the brackish- and freshwater mollusks. On the other hand, the Sakashu Faunal Group is characterized by the brackish-water mollusks. It suggests that salinity is the main differential factor between the Hauterivian faunas in the Masaki and Sakashu faunal groups. A Hauterivian mixed assemblage of the Tatsukawa and Shobu faunas was found in Central Shikoku. The finding suggests that the two faunas were formed in different salinity environment and adjoining areas.四国中・東部秩父累帯下部白亜系の非海生二枚貝類について種構成や群集の生息環境を考察し，再編された地帯区分との対応を検討した．これらの白亜紀非海生動物群は新たな秩父累帯の地帯区分及び種構成に墓づいて，互いに共通種を持たない正木動物群(Masaki Faunal Group)と坂州動物群(Sakashu Faunal Group)に区分される．正木帯に属する物部川層群の非海生二枚貝類は正木動物群に帰属し，立川フォーナ(Hauterivian)，柚ノ木フォーナ(Late Barremian)，日比原フォーナ(Early Aptian)で構成される．坂州帯に属する南海層群，竹ヶ谷層群の非海生二枚貝類は坂州動物群に帰属し，菖蒲フォーナ(Hauterivian)で特徴づけられる．四国中・東部における正木動物群は，汽水生一淡水生軟体動物で特徴づけられ，坂州動物群は汽水生軟体動物で特徴づけられる．このことは，坂州動物群は正木動物群より塩分濃度の高い環境で生息したことを示す．また，四国中央部では両動物群の混在が確認され，正木動物群と坂州動物群は，隣接して存在し，塩分濃度の異なる環境に生息したことが推測される

Stratigraphy of the Nankai Group in the Tosayamada area, Central Kochi, and correlation with the Monobegawa Group

The purpose of our study is to clarify stratigrapical correlation of the Nankai and Monobegawa Groups. This paper presents the results of srratigraphy, sedimentary facies and geologic time. The Cretaceous System of the Chichibu Terrain in the Tosayamada area is divided into the Monobegawa and Nankai Groups. The Monobegawa Group conformably overlies the Yasuba Formation(Permian) can be subdivided into three formations which are the Ryoseki, Monobe and Hibihara Formation. The Nankai Group can be subdivided into two formation which are the Funadani and lgenoki Formations. These are bounded to the North by Suita Tectonic line with serpentinite and to the South by Permian accretionary complex. The lower part of the Funadani Formation consists of 150m of massive conglomerate and sandstone. The upper part of this formation consists of black mudstone which bear ammonite and some bivalve fossils. The lgenoki Formation conformably overlies the Funadani Formation. The lower part of the Igenoki Formation consists of alternate layers sandstone and mudstone in which occur abundant bivalves and ammonites. They indicate the lower part to be Aptian. Some bivalves and ammonites are obtained from black mudstone which is the upper part of this formation. lgenoki Formation lies in fault contact with Permian accretionary complex which is named Yukigamine Formation. Stratigrafical sequences of both groups are very similar, therefore, the Nankai group is member of Kurosegawa Tarrain

Lower Cretaceous litho-and bivalve-stratigraphy of the Sakawa-Ochi area, Kochi Prefecture, SW Japan

The Ochi-Sakawa area is one of the classic fields of Paleozoic and Mesozoic stratigraphy in the tectonic Kurosegawa Belt in of Eastern Shikoku, Japan. The Mesozoic is characterized by shallow marine and brackish water deposits, in which Triassic and Jurassic shallow marine deposits are famous for their abundant megafossils, the Cretaceous deposits remaining until now largely unknown. Located within the Chichibu Superbelt* the Cretaceous formations of the Ochi-Sakawa area consists of two tectonic blocks, being separated by a north-south trending fault, within the Yoshigahira and Sakashu belts. In both blocks, the Lower Cretaceous formations consist in ascending order of the Kaisekiyama Formation (Hauterivian), the Tosakamo Formation (Barremian-Aptian), the Kurohara Formation (Aptian), and the Yotsushiro Formation (Albian). Brackish water bivalves occur in the Kaisekiyama Formation and lower part of the Tosakamo Formation. Higher up, in the in the lower and middle parts of the Tosakamo Formation, Barremian shallow marine bivalves and in the upper part of the formation, Aptian marine bivalves occur. The Kurohara Formation yields Aptian shallow marine bivalves and the Yotsushiro Formation yields Albian marine bivalves and ammonites. The Early Cretaceous faunas of the Sakawa block is characterized by the so-called Sakashu and Masaki faunal groups, while that of the Ochi block contains elements of the so-called Masaki faunal group. The differentiation of these faunas suggests a faunal transition between different environments within the Yoshigahira and Sakashu belts. *Kumosoyama, Masaki, Yoshigahira, Sakashu and Nakagawa belt

四国中央部黒瀬川帯混在型群集

The Early Cretaceous bivalve fauna from the Kurosegawa Belt in Central Shikoku was studied with respect to the faunal affinity. In the Kurosegawa Belt, two faunal-types of Hauterivian bivalves have been recognized (Kozai et al., 2002). The one, Tatsukawa-type from the Monobegawa Group is distributed in the Northern Kurosegawa Belt. Another one, Shobu-type from the Nankai and Takegatani groups is distributed in the southern Kurosegawa Belt. Based on the specific compositon, the former is regarded as "Tethyan fauna", and the later is regarded as "northern Tethyan fauna" of Tashiro (1994, 2000). The specific compositions of these two faunas are quite different except for the cosmopolitan species. A transitional fauna between the Tatsukawa-type and Shobu-type was newly discovered in Hauterivian sandstone bed of brackish facies in the north-south intermediate part of the Kurosegawa Belt. Among the six local species, Protocardia ibukii, Costocyrena otsukai, Pulsidis antiqua and Tetoria Sanchuensis are the Tatsukawa-type elements. Isodomella matsumotoi and Eomiodon matsumotoi are the Shobu-type elements. In addition to the finding of the marine Barremian "Tethyan"-"Northern Tethyan" transitional bivalve-fauna, new discovery of the Hauterivian brackish trasitional-fauna is significant for the analysis of paleobiogeography and tectonics during and after the Early Cretaceous. Especially, the existence of the transitional fauna indicates that the "Tethyan" and "Northern Tethyan" faunas are paleobiogeographicaly closer

Discovery of Triassic microfaunas at Mae-Sot, NW Thailand (Preliminary report)

The Middle and Late Triassic radiolarian faunas were extracted from a vitric tuff rich laminated bedded-chert in the Mae-Sot and Umphang areas of NW Thailand. The radiolarian faunas from the bedded-chert succession are characterized by Triassocampe postdeweveri (Early Ladinian), Pachus multinodosus (Early Norian), Sarla natividadensis (Middle Norian) and Canoptum rhaeticum (Norian-Rhaetian), individually. The Triassic chert-sequence is overlain by the ‘Jurassic base-conglomerate’, an ill-sorted breccia in a reddish-silt matrix. The limestone and chert clasts in the conglomerate yield Early - Late Triassic conodonts and Middle - Late Triassic radiolarians, respectively. Chert clasts in the conglomerate yield among others Norian - Rhaetian radiolarians like Pachus multinodosus and Canoptum rhaeticum, while Early - Late Triassic conodonts as Platyvillosus costatus, Cratognathodus cf. cuspidatus, Metapolygnathus polygnathiformis, M. carpathicus, Ancyrogondolella quadrata and A. spatulata are found in limestone clasts. The silici-pelagic origin of the clasts suggests the presence of an ocean before the end Triassic orogeny along the Mae Sariang Zone that amalgamated the parts of the Shan-Thai block. This first finding of Late Triassic (Norian - Rhaetian) radiolarians from bedded-cherts, next to the Middle Triassic and older radiolarian faunas, adds another element to the reconstruction of the sequence now comprised in the Mae Sariang Zone, W of the Nan-Uttaradit Suture. The occurrence of Triassic limestone, as that of the Chaiburi Formation in the Phatthalung area of the Mae Sariang Zone or the Kodiang Limestone in the ‘Western zones’, may elucidate the question about the provenance of the Triassic conodont-bearing limestone clasts in the Jurassic base-conglomerate that seals the Mae-Sariang Zone. The newly dated Triassic sequence is further sealed by the continental-shelf deposits of the Toarcian - early Bajocian Hua Fai Group

Jurassic-Cretaceous boundary and Cretaceous formations in the Tosayamada-Birafu area, Kochi Prefecture

見学コースは，香美市土佐山田町から香美市香北町にかけて分布する黒瀬川帯南帯の地層見学で，田代（1985）による南海層群の模式地とされている地域である．南海層群の地帯帰属を考察するために，南海層群の南側に分布するペルム紀付加体，南海層群基底部礫岩，テチス型二枚貝フォーナとされている二枚貝類の産出地点を観察する．その後，南海層群と断層で接し，ジュラ紀後期から白亜紀最前期の地質年代を持つ美良布層模式地に移動し，Kilinora spiralis群集，Loopus primitivus群集，Pseudodictyomitra carpatica群集の放散虫と海生・汽水生の二枚貝類の産出層準を見学するとともに砕屑岩・石灰岩からなる堆積相を観察する．また，美良布層のジュラ系白亜系境界についても検討する

トクシマケンサン コッカイ ギジドウ ダイリセキ ノ ケンキュウ 3 シュウサン リョウイン ニオケル セキザイ シヨウ ノ ヒカク

Marbles from Tokushima Prefecture that decorate the National Diet Building of Japan (Nagata-cho, Tokyo) were compared directly for the first time about the use of the seven brands in the House of Representatives and the House of Councilors. The seven brands, “Akebono”, “Kito-ishi”, “Hototogisu”, “Kamo-sarasa”, “Awayuki”, “Kotajima” and “Shin-awayuki” were verified that they were used symmetrically in both the House of Representatives and the House of Councilors including the central part of the building. The “Akebono”, Silurian limestone of the Kurosegawa Tectonic Zone from Koyamadaira (Sakashu, Naka-cho), is used on the wall of the Diet members’ Second Stairway. The “Kito-ishi”, limestone breccia intercalated in Late Carboniferous chert facies from Misago-Yama (Sakashu, Naka-cho), is used for the fireplaces in the reception rooms of the Vice-presidents. The “Hototogisu”, Late Triassic dolimitic limestone in the earliest Cretaceous accretion mélange from Arida (Asebi-cho, Anan City) of the South Chichibu Belt (Tsunomine Subbelt), is used for the well-ornamented entrance frame of the Emperor’s room “Gokyujo”. The “Kamo-sarasa”, latest Triassic intramicrite from Oji (Kuwano-cho, Anan) of the Tsunomine Subbelt, is used on the wall inside the central entrance of the building, and door frames of rooms in both houses. The “Awayuki”, Late Triassic gray limestone with Megalodon and dark blocks of hexa-corals from Kurogo (Kamo-cho, Anan City) in Tsunomine Subbelt, is used for the base of the wall along the square in front of the Emperor’s room, and the base of pillars around the central hall, as well as the lower part of the wall around the assembly hall of both houses. The “Kotajima”, black cleavaged Norian limestone from Higashibun (Tsunomine-cho, Anan City) in the Early Cretaceous olistostrome of the Tsunomine Subbelt, is used on the lower part of the wall along the passage of the third floor in both houses, and walls of the “Kisha Kaidan” stairways to both galleries. The “Shin-awayuki”, Late Carboniferous limestone from the Izeki (Takarada-cho, Anan City) in Jurassic accretionary mélange of the South Chichibu Belt (Hosono Subbelt), is used for the mosaic on the floor of the Central Hall

シコク トウブ ナンブ クロセガワタイ サカシュウタイ ノ クリサカソウ トドロ セクション ニオケル ジュラキ コウキ ホウサンチュウ ソウジョ ト アンモナイト ネンダイ

The LAD (last appearance datum) of the radiolarian Kilinora spiralis (Matsuoka，1983) is found to concur with the FAD (first appearance datum)of the ammonite Ataxioceras (Ataxioceras) kurisakense Kobayashi and Fukada，1947 in the Todoro Section of the Kurisaka Formation，Southen Kurosegawa Terrane (Sakashu Belt)， Shikoku，SW Japan. Providing a clue to the still pending chronological discrepancy between European and North American radiolarian zones，the constraint by ammonite age prolongs the range of the Kilinora spiralis Zone，a remarkable Upper Jurassic radiolarian zone in Japan -NW Pacific region，into the Lower Kimmeridgian

Significance of the direct correlation of ammonite and radiolarian zones in the Izumi Group for integrated biostratigraphy of Late Cretaceous NW paleo-Pacific region

The direct correlation of radiolarian and ammonite zones in the Izumi Group were reviewed and revised for integrated biostratigraphy across the Campanian – Maastrichtian boundary. The significance of the direct correlation between mega- and micro-, i.e. between relatively near-shore nektonic and slope-basin planktonic faunas in the same stratigraphic field, was discussed in relation with the litho- and biofacies of the group. The Late Cretaceous ocean climate change and surface seawater current inferred from the radiolarian fauna was considered as a marker event for the chronostratigraphic correlation in the middle latitude continental shelf to slope-basin facies facing towards the NW paleo-Pacific