Cenomanian (Upper Cretaceous) carbon isotope stratigraphy of terrestrial organic matter for the Yezo Group, Hokkaido, Japan

Abstract

Carbon isotope fluctuations of sedimentary organic matter along the two geological traverses in the Yezo Group, Hokkaido, northern Japan, elucidate a detailed chemostratigraphy for the Cenomanian Stage on the northwestern Pacific margin. Visual characterization of the kerogen from mudstone samples shows that the major constituents of sedimentary organic matter originated as terrestrial higher plants. The atomic hydrogen/carbon ratios of the kerogen suggest that the original d 13 C values of terrestrial organic matter (TOM) have not been affected significantly by thermal diagenesis. The patterns in two d 13 C TOM curves are similar and independent of changes in lithology and total organic carbon contents, which suggests that TOM was mixed sufficiently before the deposition in the Yezo forearc basin for the d 13 C composition having been homogenized. In addition, this implies that the Hokkaido d 13 C TOM profiles represent the averaged temporal d 13 C variations of terrestrial higher-plant vegetation in the hinterlands of northeast Asia during Cenomanian time. Three shorter-term (ca. 0.1 my duration) positive-and-negative d 13 C TOM fluctuations of~1‰ are present in the Lower to Middle Cenomanian interval in the Yezo Group. On the basis of the age-diagnostic taxa (ammonoids, inoceramids and planktic foraminifers), these discrete d 13 C TOM events are interpreted to be correlated with those in the d 13 C curves of pelagic carbonates from European basins. The correlation of d 13 C events between the European and Yezo Group sections suggests that the shorter-term d 13 C fluctuations in Cenomanian ocean-atmosphere carbon reservoirs are useful for global chemostratigraphic correlation of marine strata. In particular, the correlation of d 13 C fluctuations of the so-called 'Mid-Cenomanian event' (MCE) implies: (i) the d 13 C variations of global carbon reservoir during the MCE are precisely recorded in the d 13 C TOM records; and (ii) the MCE d 13 C TOM event is an efficient chronostratigraphic index for the Lower/ Middle Cenomanian boundary of the Mid-Cretaceous sequences.

A revised inoceramid biozonation for the Upper Cretaceous based on high-resolution carbon isotope stratigraphy in northwestern Hokkaido, Japan

“…The Hydrogen Index (HI) is the ra- Haboro R. Haboro R. The study areas. The northern rectangle is the Haboro area, the southern area is the Obira area, the middle rectangle with dashed line (a) is the Kotanbetsu area studied by Takashima et al (2010), and the southern rectangle with dashed line (b) is the area studied by Uramoto et al (2007Uramoto et al ( , 2009). (C) Geological map of the Haboro area.…”

“…9. Correlation of the stratigraphic distribution of inoceramid zones and the δ 13 C TOM curves of the Yezo Group (Haboro area: this study; Obira area: composite curve of Hasegawa and Saito, 1993;Uramoto et al 2007Uramoto et al , 2009 and this study (black line)). Correlations of the carbon isotope fluctuations are indicated by the dashed lines.…”

“…10. Correlation of the carbon isotope stratigraphy between the Haboro and Obira areas (this study; Hasegawa and Saito 1993;Uramoto et al 2007Uramoto et al , 2009), Kotanbetsu area (Takashima et al, 2010), Salzgitter Salder and Söhlde secton (Voigt and Hilbrecht 1997), Lägerdorf-KronsmoorHemmoor succession (Voigt et al 2010) and the English Chalk (Jarvis et al 2002(Jarvis et al , 2006. Correlations of the carbon isotope fluctuations are indicated by the grey bands and dashed lines.…”

“…The carbon isotope profile after Hasegawa and Saito (1993); Uramoto et al (2007Uramoto et al ( , 2009 The carbon isotope profile after Hasegawa and Saito (1993); Uramoto et al (2007Uramoto et al ( , 2009 Inoceramid biozones after Funaki and Hirano (2004) Inoceramid biozones after Funaki and Hirano (2004) Text- fig. 10.…”

“…Temporal fluctuations in the carbon isotope ratios (δ 13 C) of marine carbonates are a reliable tool for regional and international correlations (e.g., Jenkyns et al 1994;Erbacher et al 1996;Voigt and Hilbrecht 1997;Stoll and Schrag 2000;Voigt 2000;Jarvis et al 2002Jarvis et al , 2006Voigt et al 2010). In Japan, δ 13 C stratigraphic studies on terrestrial organic matter have been undertaken for the Yezo Group (Hasegawa 1992;Hasegawa and Saito 1993;Hasegawa 1997;Hirano and Fukuju 1997;Hasegawa and Hatsugai 2000;Ando et al 2002Ando et al , 2003Hasegawa et al 2003;Ando and Kakegawa 2007;Uramoto et al 2007Uramoto et al , 2009Takashima et al 2010). Hasegawa (1997) discussed the resemblance between the δ 13 C curves for marine carbonates and those for terrestrial organic matter, and concluded that the δ 13 C stratigraphy of terrestrial organic matter provides a reliable tool for correlation with the marine carbonates.…”