No abstract

Bacterial endospores are dominant members of the marine deep biosphere.

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.

Stratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian-Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive δ 13 C fluctuations for the Cenomanian-Turonian boundary, the Middle Turonian, the upper Turonian-lower Coniacian, and the Santonian. A biostratigraphic framework of the agediagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these δ 13 C fluctuation events are comparable with those recorded in δ 13 C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these δ 13 C events in terms of global chemostratigraphy. In particular, the δ 13 C patterns within the overall positive interval of the Cenomanian-Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of δ 13 C fluctuation patterns demonstrates that the terrestrial organic δ 13 C data mirror the global-scale δ 13 C patterns in the carbon reservoir of oceanatmosphere-terrestrial biosphere during the Cenomanian-Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic δ 13 C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic δ 13 C events appears more amplified than that of coeval marine carbonate δ 13 C events. This correlation is interpreted to mean that the effects of local CO 2 emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global δ 13 C trend and resulted in the terrestrial organic δ 13 C records of the Yezo Group.