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

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．ArticleJournal of the Sedimentological Society of Japan. 70(2):63-69 (2011)journal articl

The sedimentary imprint of Pleistocene glacio-eustasy: Implications for global correlations of seismic sequences

We evaluate lithofacies, chronology, and seismic sequences from the Canterbury Basin, New Zealand passive continental slope (Integrated Ocean Drilling Program [IODP] Expedition 317 Site U1352 and environs) and compare this with slope sequences from the New Jersey passive margin. Our goal is to understand continental slope sedimentation in response to glacio-eustasy and test the concepts of sequence stratigraphy. High-resolution geochemical elemental and lithostratigraphic analyses were calibrated to a chronology constructed from benthic foramininferal oxygen isotopes for the past ~1.8 m.y. We identify lithofacies successions by their unique geochemical and lithologic signature and correlate them with marine isotope stages (MIS) at Milankovitch 100 k.y. (MIS 1–12) and 41 k.y. (MIS 13–63) periods. Eight seismic sequence boundaries (U13–U19) were identified from high-resolution multichannel seismic data, providing a seismic stratigraphic framework. Except for MIS 1–5 and MIS 54–55, there are 2–16 MIS stages and a comparable number of lithofacies contained within each seismic sequence, indicating that it took one to several glacio-eustatic cycles to build each seismic stratigraphic sequence. These findings support prior results obtained by the Ocean Drilling Program (ODP) Leg 174A on the New Jersey continental slope. On both margins, there is a strong correlation between seismic sequences, lithofacies, and MIS, thus linking them to glacio-eustasy. However, the correlation between MIS and seismic sequences is not one-to-one, and Pleistocene seismic sequences on the two margins are not synchronous. Local conditions, including differences in sedimentation rates and creation of accommodation space, strongly influenced sediment preservation at each location, revealing that high-frequency Pleistocene seismic sequences need not correlate globally

Channel-Fill Conglomerates in the Middle Miocene Kotambetsu Formation, Northern Hokkaido, Japan

The Middle Miocene Kotambetsu Formation consisting of turbidite and related coarse clastic sediments, attains to 2,000 meters in thickness. Conglomerates in this formation are channel-fill deposits with normal or inverse type graded-bedding and clast fabrics. The clast fabrics are characterized by inclining orientation of the long axes to the bedding plane. Analysis of the sedimentary structures suggests that the coarse clastic sediments of the Kotambetsu Formation were transported by the sediment gravity flows of turbidity currents

Grain size description of sediments from ODP Leg 174A sites

We drilled three sites (Sites 1071, 1072, and 1073) on the New Jersey shelf and slope at water depths between 88 and 664 m. Grain-size analyses from shelf sites (Sites 1071 and 1072) define five types of sediment: well-sorted fine sand, silty sand or sandy silt, clayey silt, poorly sorted sandy mud, and poorly sorted lag sediments. At slope Site 1073, a grain-size minimum of 3-6 µm is found at 300 meters below seafloor. These sediments are well sorted and lack sand- and clay-sized grains. Horizons of coarse-grained sediments are present in Unit I at Site 1073