Molecular geochemical approach to the Paleoceanographic assessment of Neogene sediments of Yashima area, Akita Basin, Japan.

Yamamoto, Masanobu; Watanabe, Yoshio

doi:10.3720/japt.60.27

Cited by 6 publications

(4 citation statements)

References 10 publications

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“…Changes in the marine environment affect primary productivity and organic matter preservation, which can influence the formation of petroleum source rocks (Tada, 1994(Tada, , 1995Yamamoto and Watanabe, 1995). Stein (1991) proposed two models for the formation of source rocks.…”

Section: Introductionmentioning

confidence: 99%

“…To fully elucidate the source rock formation mechanism in the Akita Basin, it is necessary to also consider tectonics and paleogeography. Paleoceanographic reconstructions from organic biomarkers have only been produced for the Yashima and Shinjo areas (Taguchi et al, 1986;Yamamoto and Watanabe, 1995). Additionally, it is difficult to provide age constraints for the Onnagawa and Kusanagi formations using diatom biostratigraphy because the tests are generally affected by diagenesis (i.e., dissolution).…”

Section: Introductionmentioning

confidence: 99%

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Spatio-temporal changes in the depositional environment of Miocene organic rich mudstones in the Akita Basin deduced from biomarker analysis

et al. 2022

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Paleoceanographic changes in the Akita Basin during the Miocene were investigated using biomarker analysis of source rocks from the Onnagawa and Kusanagi formations in the Yashima area (eastern basin margin) and the Shonai Plain (central basin). During the Nishikurosawa Stage (~13 Ma), the homohopane index indicated a slightly oxidizing depositional environment. At this time, the Japan Sea was an open marginal sea and an oxidizing environment; thus, organic matter preservation in the Akita Basin was low. In the Early Onnagawa Stage (~12 Ma), the Japan Sea became semi-closed because of uplift of the proto-Northeastern Japan Arc. This change is reflected in the pristane/phytane ratio and homohopane index that suggest the Yashima and Shonai Plain areas became reducing, which enhanced organic matter preservation. The depositional environment of the Kusanagi Formation (Shonai Plain) was more reducing than that of the Onnagawa Formation (Yashima area). During the Middle Onnagawa Stage (10 Ma), the homohopane index showed that the Onnagawa Formation (Yashima area) had shifted to an oxidizing depositional environment. Additionally, the C 27 /C 27 + C 29 sterane ratio indicated that algae were responsible for the higher overall primary production in the Middle Onnagawa Stage. This high primary productivity was associated with localized coastal upwelling, which resulted in generally high organic matter content in the Middle Onnagawa Formation. In the Shonai Plain area (Kusanagi Formation), bottom water conditions remained anoxic; however, sedimentary organic matter content did not increase because there was no upwelling in the area. During the Late Onnagawa Stage (8 Ma), the seafloor environment in the Shonai Plain area also became oxidizing. As a result of enhanced organic matter decomposition, overall sedimentary organic matter content decreased.Our results demonstrate that local variations in primary productivity and bottom water conditions are recorded in the sedimentary record and emphasize the importance of geographic and tectonic settings to the deposition and preservation of organic-rich source rocks. Thus, this study was able to describe spatio-temporal changes over the entire Akita Basin.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spatio-temporal changes in the depositional environment of Miocene organic rich mudstones in the Akita Basin deduced from biomarker analysis

et al. 2022

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“…Iijima & Tada 1990;Tada 1991;Koizumi 1992). In addition, organic geochemical data have been used for reconstructing paleoceanographic conditions from Miocene to Pliocene hemipelagic sediments of the Akita, Yamagata and Niigata areas (Stein & Stax 1992;Yamamoto & Watanabe 1995;Yamamoto et al 1999). Using biomarker analysis, Yamamoto et al (1999) reported the million-year scale variations in paleoproductivity controlled by sea surface and bottom redox conditions in the hemipelagic sediments of Tohoku Trough.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructions

Sawada

2006

Island Arc

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Organic petrological observations of kerogen macerals and organic geochemical analyses of carbon isotopes of kerogen macerals and biomarkers were conducted on Neogene neritic sediments of the Takafu syncline area of central Japan. The Senmi, Sakainomiya and Lower Shigarami Formations in that area were deposited at the neritic provinces on the southern edge of the paleo-Japan Sea during the Late Miocene to Early Pliocene. Sedimentary organic matter in these formations was almost terrigenous in origin. Changes in kerogen maceral compositions reflect sedimentological and tectonic histories evaluated in previous studies from sedimentary facies and paleontology. It was found that carbon isotope ratios (δ 13 C) of kerogen macerals increased from −28‰ to −25‰ from the Sakainomiya to the lower part of the Lower Shigarami Formations. The cause of that increase was presumably the expansion of C 4 plants into southwest Japan. The timing was concordant with that of the expansion of C 4 plant grasslands in East Asia. The oxicity (oxic to anoxic) conditions of sea bottoms evaluated from pristane/phytane ratios varied. Particularly, in the lower part of the Senmi Formation, layers in which no steroid biomarkers could be detected were found, and had presumably formed under oxic conditions when strong biodegradation had occurred. Concentrations of regular (C 27 -C 29 ) steranes and dinosteranes were higher in the Sakainomiya and Lower Shigarami Formations. This indicates that dinoflagellates-dominant primary productions were higher at those stages. In addition, concentrations of diatomaceous biomarkers such as C 26 norsterane increased from the Lower Shigarami Formation, thus adding diatoms to the major producers. Furthermore, similar associations between the increases of δ 13 C values of kerogen macerals and concentrations of diatomaceous biomarkers were observed in the Takafu syncline area. Thus, the expansion of C 4 plants was possibly associated with the high production of diatom in the shallow-marine areas of the paleo-Japan Sea during the Neogene Period.

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Carbon isotope signatures of bacterial 28-norhopanoic acids in Miocene–Pliocene diatomaceous and phosphatic sediments

et al. 2005

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Molecular geochemical approach to the Paleoceanographic assessment of Neogene sediments of Yashima area, Akita Basin, Japan.

Cited by 6 publications

References 10 publications

Spatio-temporal changes in the depositional environment of Miocene organic rich mudstones in the Akita Basin deduced from biomarker analysis

Spatio-temporal changes in the depositional environment of Miocene organic rich mudstones in the Akita Basin deduced from biomarker analysis

Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructions

Carbon isotope signatures of bacterial 28-norhopanoic acids in Miocene–Pliocene diatomaceous and phosphatic sediments

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