@article{oai:soar-ir.repo.nii.ac.jp:00018259, author = {Yoshida, Mamiko and Inoue, Hirobumi and Hoyanagi, Koichi and Yanagisawa, Yukio and Oishi, Masayuki and Yoshida, Hiroo}, issue = {2}, journal = {Journal of the Sedimentological Society of Japan}, month = {}, note = {This paper discusses relationship among depositional environments, origin of the sedimentary organic matter and diatom fossil assemblage, combined with sequence stratigraphy in an incised-valley system. Interpretation of the environments and their changes was based on sedimentary facies, total sulfur (TS) content, and diatom assemblages. The quantity and composition of organic matter were estimated for the environmental interpretation on the basis of the total organic carbon (TOC) content, reflected-light fluorescent microscopy, and stable carbon isotope ratios of the organic matter (δ13Corg). The Miocene to Pliocene Ishibane, Tatsunokuchi and Motohata formations in northeast Japan consist of estuarine and fluvial deposits that were formed during a rise and fall of sea level. The proportions of vitrinite and cutinite that are coarse-grained and terrestrial in origin are relatively high in fluvial deposits of the lowstand systems tract. The proportion of marine alginite, TOC content, and δ13Corg values increase upward in estuary deposits of the transgressive systems tract. This implies the increase in the influence of the sea and the estuarine bottom conditions becoming anoxic. The proportions of vitrinite and cutinite increase upward in the highstand systems tract, whereas the δ13Corg values and TOC content decrease upward. These reflect the strong influence of river discharge. Variations of diatom fossil assemblage of fresh water, brackish water, intertidal, coastal marine and open marine species indicate the same repetitions of transgression and regression in the Tatsunokuchi Formation. Therefore, the transgressive systems tract in the Tatsunokuchi Formation includes four cycles of transgression and regression, while highstand systems tract shows one cycle of transgression and regression. / 岩手県南部の北上市に分布する中新統~鮮新統の石羽根,竜の口,本畑層は,エスチュアリーと河川環境での堆積を示している.また,1回の海水準上昇と引き続く低下で堆積した地層で,低海水準期堆積体,海進期堆積体,高海水準期堆積体に区分できる.その周期は約100万年と推定できる.河川成堆積物からなる低海水準期堆積体では陸源有機物片を多く含み,有機物は低い安定炭素同位体比(δ13Corg)を示す.引き続くエスチュアリー環境を示す海進期堆積体では,上方に向かって,海棲有機物が増え,δ13Corgの値が大きくなり,さらに全有機炭素量も増加する傾向にある.海進初期ではこれらは,小さな増減を4回繰り返しているが,やがて最大海進面に向かって安定して増加するようになる.最大海進面より上位の高海水準期堆積体では陸源有機物量が増大し,δ13Corgと全有機炭素量は減少し,陸域からの物質供給が増加したことが示される.珪藻化石の淡水種,汽水種,潮間帯種,沿岸性種,外洋種の比率変化も同一の海進海退の繰り返しを竜の口層中に記録している.したがって,竜の口層の海進期堆積体は短周期の4回の海進海退と引き続く海進から構成され,一方,高海水準期堆積体は1回の海退を示す.これらは数10万年周期の海水準変動に対応するかもしれない., Article, Journal of the Sedimentological Society of Japan. 70(2):63-69 (2011)}, pages = {63--69}, title = {High-resolution sequence stratigraphy in an incised-valley system on the basis of sedimentary organic matter, sulfur content and fossil diatom: An example from Miocene to Pliocene Tatsunokuchi Formation, Iwate Prefecture, Northeast Japan}, volume = {70}, year = {2011} }