Diagenesis of Neogene diatoms and their importance as a source of petroleum in Japan

Abstract

Various siliceous rocks are found in the Ohdoji, Akaishi and Maido Formations from the western Aomori basin, and the Yotsuzawa and Wadagawa Formations from the eastern Aomori basin of northern Honshu, Japan. These rocks are classified into diatomite, siliceous shale and chert.Diatomite is composed of abundant amorphous silica and has porosity between 50 and 65%. Siliceous shale is composed of a large amount of quartz, and has porosity ranging from 25 to 35%. Chert is chiefly composed of cristobalite or quartz, and has porosity between 20 to 30%.Average contents of total organic carbon, S,, and S, generally increase from argillaceous rocksdiatomitessiliceous shalescherts. Maturation of organic matter in these rocks is generally lower than that in average source rocks. Diatoms, which appeared in the late Cretaceous and became increasingly important in the Miocene, are the principal primary producers of organic matter in the marine environment during the Cenozoic. Excellent organic components and higher biological productivity show that diatoms might be the most important source of petroleum during the Neogene in Japan. Proteins, carbohydrates and lipids in diatoms have been transformed into fulvic acids, humic acids and humin by polycondensation and polymerization. Later, these humin materials could be changed into insoluble kerogen under the effect of mild temperature and pressure. A part of the lipids would transform to geochemical fossils (biomarkers). Amorphous silica in cells of diatoms would change to low-cristobalite and low-quartz by the increase of geothermal temperature.

Slip Inversion Along Inner Fore‐Arc Faults, Eastern Tohoku, Japan

“…Stratigraphy of the region surrounding the Noheji Fault (after Aoyagi & Omokawa, ; Kamada et al, ; Tsushima, ). (a) U‐Pb zircon, this study ; (b) Bo‐P tephra (Machida et al, ; Miyauchi, ); (c) K‐Ar (Kudo, ); and (d) Diatom Zone N14‐N15 (Aoyagi & Omokawa, ).…”

“…Sections were rejected if model and observed bedding dips differed by more than~10°or if model and Figure 6. Stratigraphy of the region surrounding the Noheji Fault (after Aoyagi & Omokawa, 1993;Kamada et al, 1990;Tsushima, 1962). (a) U-Pb zircon, this study; (b) Bo-P tephra (Machida et al, 1985;Miyauchi, 1988); (c) K-Ar (Kudo, 2005); and (d) Diatom Zone N14-N15 (Aoyagi & Omokawa, 1993).…”

Infrared Microspectroscopy of Bionanomaterials (Diatoms) with Careful Evaluation of Void Effects

“…[12][13][14] They play a key role in the regulation of the biogeochemical cycle of silicon in the modern ocean, 15,16 and they are an important origin of petroleum and natural gas. [17][18][19][20] The diatom cell wall is composed of mainly hydrous amorphous silica (SiO 2 .nH 2 O) with a small portion of organic macromolecules (proteins and polysaccharides) ( Figure 1a). [21][22][23] Because of beautiful nano and micro-scale structures of diatoms ( Figure 2), they are often regarded as model materials for nano-patterning and nano-fabrication.…”

Decrease of aliphatic CHs from diatoms by in situ heating infrared microspectroscopy

“…Silica is also transformed from amorphous hydrous silica (Opal‐A) via cristobalite (Opal‐C) to quartz (Qz) reactions [ Pollastro , ; Lynne et al ., ]. Diatoms are considered to be one of the major sources of oil and gas together with other small aquatic organisms such as radiolaria and foraminifera [ Aoyagi and Omokawa , ; Aoyagi and Omokawa , ; Theriot , ; Levitan et al ., ]. Generation of hydrocarbons is thus considered to be related to transformation of organic components in aquatic organisms such as diatoms during their burial and diagenesis [ Tissot and Welte , ].…”