Terrestrial and marine organic matter evidence from a Cretaceous deep-sea chert of Japan: Implications for enhanced hydrological cycle during the Aptian OAE 1a

The early Aptian Oceanic Anoxic Event (OAE 1a; ca. 120 Ma) was accompanied by a massive eruption of the Ontong Java Plateau, doubling atmospheric pCO2, and increasing sea surface temperature by 4-8 C. In this study, we attempted a palynological analysis of the Hauterivian to Cenomanian deep-sea chert from the Goshikinohama site, and successfully obtained a variety of microremains, mainly represented by amorphous organic matter, aggregations of organic and inorganic particles, and cuticle fragments. One Hauterivian and many Aptian samples unexpectedly yielded terrestrial plant material, such as resins and wood fragments with tracheids, which represent the first record of terrestrial plant microremains from deep-sea pelagic chert. The occurrence of wood fragments within the negative and positive delta 13C excursions during the OAE 1a can be correlated with an interval of increased atmospheric CO2 level. We can also suggest that the occurrence of resins, mainly within the mudstone-rich chert intervals of the early Aptian negative delta 13C peak and the middle-upper Aptian interval, are possibly related with periods with sea-level drops. Similar massive resin deposition events have been linked with intensified hydrological cycling during other abrupt climatic disruptions, such as the Carnian Pluvial Event, the Triassic-Jurassic boundary, and the Paleocene-Eocene Thermal Maximum. There-fore, an increase of terrestrial plant burial in deep-sea chert is likely linked with a massive plant discharge related with enhanced hydrological cycles, such as intensified storms and/or some sea-level change during the OAE 1a.

Automated summary

This study conducted a palynological analysis of deep-sea chert from the Hauterivian to Cenomanian period at the Goshikinohama site. Various microremains were obtained, including amorphous organic matter, organic and inorganic particle aggregations, and cuticle fragments. Surprisingly, terrestrial plant material such as resins and wood fragments were found in both the Hauterivian and Aptian samples, representing the first record of such remains in deep-sea pelagic chert. The occurrence of these terrestrial plant materials can be correlated with increased atmospheric CO2 levels and periods of sea-level drops.