10:45 AM - 11:00 AM
[SGL22-06] The Paleocene to early Eocene integrated stratigraphy of dinoflagellate cyst and carbon isotope in the Nemuro Group in eastern Hokkaido, Japan
Keywords:Paleocene, Eocene, Paleogene, Nemuro Group, dinoflagellate cyst, carbon isotope stratigraphy
The early Paleogene is known as the warmest period in the Cenozoic, and is regarded as the latest example of greenhouse climate condition. It is reported that the long-term (~1 m.y. scale) and the short-term (~10 k.y. scale) paleoclimatic and paleoenvironmental disturbances frequently occurred in the early Paleogene period. Particularly, the Paleocene-Eocene Thermal Maximum (PETM) is well known as the prominent short-term global warming event at the Paleocene-Eocene boundary. This event is characterized by sharp and abrupt negative excursion about 2-4‰ in stable carbon isotope stratigraphy, which is named Carbon Isotope Excursion (CIE).
The Nemuro Group, which is widely distributed in the Shiranuka Hill, eastern Hokkaido, is a forearc basin sediment of the Paleo-Kuril Arc during the Late Cretaceous to Early Paleogene. The Tomikawa Formation, the uppermost part of the Nemuro Group, is mainly composed of dark gray sandy mudstone and frequently intercalations of turbidite sandstone and conglomerate. In this study, we examined the integrated stratigraphy of dinoflagellate cyst and stable carbon isotope of the Tomikawa Formation, because of the formation is considered to be formed during early Paleocene to early Eocene.
As a result, the dinoflagellate cyst assemblages from the Tomikawa Formation consist of cosmopolitan species and some bipolar mid- and high-latitude species lived in the early Paleogene. In this study, we established 7 dinoflagellate cyst zones based on the dinoflagellate cyst assemblage changes. And we also revealed that the studied interval of the Tomikawa Formation is correlated to the late Danian to the early Ypresian.
On the other hand, stable carbon isotope ratios of bulk wood in the Tomikawa Formation generally range from -23 to -27‰. The carbon isotope ratio in the lower part of the formation shows a relatively low value of -27 to -25‰. After that, carbon isotope ratio gradually drifted toward -25 to -23‰ in the middle part of foramation, and turned to decrease again toward the top. During this period, several remarkable negative peaks were recognized.
The stable carbon isotope curves of the Tomikawa Formation and the compiled curve of the deep-sea benthic foraminifera show similar patterns of isotopic fluctuation, allowing the correlation of the carbon isotopic events between these sections. This high-resolution correlation reveals that global events, such as the Late Danian Event (LDE), Early Late Paleocene Event (ELPE), and stage boundaries of the Paleocene. In addition, it is considered that the significant negative excursion (~-31‰) in the latest Paleocene to earliest Eocene interval, which indicated by dinoflagellate cyst stratigraphy, is CIE of PETM. However, the “Apectodinium acme”, which is well known bioevent of the dinoflagellate cyst in PETM interval, is not occur around this horizon in the Tomikawa Formation. It is required more research to determine the PETM horizon and Paleocene-Eocene boundary.
The Nemuro Group, which is widely distributed in the Shiranuka Hill, eastern Hokkaido, is a forearc basin sediment of the Paleo-Kuril Arc during the Late Cretaceous to Early Paleogene. The Tomikawa Formation, the uppermost part of the Nemuro Group, is mainly composed of dark gray sandy mudstone and frequently intercalations of turbidite sandstone and conglomerate. In this study, we examined the integrated stratigraphy of dinoflagellate cyst and stable carbon isotope of the Tomikawa Formation, because of the formation is considered to be formed during early Paleocene to early Eocene.
As a result, the dinoflagellate cyst assemblages from the Tomikawa Formation consist of cosmopolitan species and some bipolar mid- and high-latitude species lived in the early Paleogene. In this study, we established 7 dinoflagellate cyst zones based on the dinoflagellate cyst assemblage changes. And we also revealed that the studied interval of the Tomikawa Formation is correlated to the late Danian to the early Ypresian.
On the other hand, stable carbon isotope ratios of bulk wood in the Tomikawa Formation generally range from -23 to -27‰. The carbon isotope ratio in the lower part of the formation shows a relatively low value of -27 to -25‰. After that, carbon isotope ratio gradually drifted toward -25 to -23‰ in the middle part of foramation, and turned to decrease again toward the top. During this period, several remarkable negative peaks were recognized.
The stable carbon isotope curves of the Tomikawa Formation and the compiled curve of the deep-sea benthic foraminifera show similar patterns of isotopic fluctuation, allowing the correlation of the carbon isotopic events between these sections. This high-resolution correlation reveals that global events, such as the Late Danian Event (LDE), Early Late Paleocene Event (ELPE), and stage boundaries of the Paleocene. In addition, it is considered that the significant negative excursion (~-31‰) in the latest Paleocene to earliest Eocene interval, which indicated by dinoflagellate cyst stratigraphy, is CIE of PETM. However, the “Apectodinium acme”, which is well known bioevent of the dinoflagellate cyst in PETM interval, is not occur around this horizon in the Tomikawa Formation. It is required more research to determine the PETM horizon and Paleocene-Eocene boundary.