5:15 PM - 6:30 PM
[MIS16-P24] High latitude paleoenvironments in Southern Hemisphere during mid-Cretaceous
Cretaceous is known as a period of warm climate with higher sea levels and higher carbon dioxide concentrations than the present, as well as with active oceanic crust formation and volcanic activity. They were especially prominent during Mid-Cretaceous Cenomanian (100.5-93.9 Ma).
Paleoenvironmental studies of the mid-Cretaceous have been conducted mainly in Europe and North America. In those areas, where global environmental changes such as oceanic anoxic events (OAEs) associated with isotope events and cyclic environmental changes derived from orbital forcing of Milankovitch cycle were recognized. In contrast, few studies have been reported in the high latitudes in the southern hemisphere. In high latitudes environmental changes more sensitive to global warming could be recorded. Can they be recognized actually? If yes, how can they be recorded, and can the magnitude and cyclicity be deciphered? This study analyzed the Cenomanian samples from the high latitudes in the Southern Hemisphere. It is a stage that typical Cretaceous greenhouse paleoenvironment developed, under ice-free condition.
This study used core samples from IODP Exp,369 Site U1516C Cores 34R and 35R, which are estimated to be deposited during mid-Cenomanian based on biostratigraphy. For high-resolution analysis, organic carbon isotope ratio (d13Corg), total organic carbon (TOC), total nitrogen (TN) and C/N ratio were obtained and discussed. Biomarker analysis, focused on specific markers such as alkenones that were interpreted to be related to surface productivity. The following were discussed and concluded.
(1) The d18O variations in sea surface temperature as large as 4°C found by previous study did not have concordant fluctuation with the terrestrial and seafloor environmental changes shown by TOC and d13Corg variations. Land and seafloor were controlled by separate factors.
(2) The variations in d13Corg can be interpreted to be partly related to the redox conditions of the seafloor, rather than being controlled by the mixing ratio of terrestrial and marine in origin.
(3) C37 alkenones derived from haptophytes were recognized. The detection of C37 alkenone with two-unsaturation sites and the absence of that with three-unsaturation sites. These facts suggest that the sea surface temperature at that time may have been higher than the current equatorial water temperature (>28°C) even in the high latitude. Negative correlation of C40 alkenones with d18O of carbonate indicates its potential significance for paleothermometry.
Paleoenvironmental studies of the mid-Cretaceous have been conducted mainly in Europe and North America. In those areas, where global environmental changes such as oceanic anoxic events (OAEs) associated with isotope events and cyclic environmental changes derived from orbital forcing of Milankovitch cycle were recognized. In contrast, few studies have been reported in the high latitudes in the southern hemisphere. In high latitudes environmental changes more sensitive to global warming could be recorded. Can they be recognized actually? If yes, how can they be recorded, and can the magnitude and cyclicity be deciphered? This study analyzed the Cenomanian samples from the high latitudes in the Southern Hemisphere. It is a stage that typical Cretaceous greenhouse paleoenvironment developed, under ice-free condition.
This study used core samples from IODP Exp,369 Site U1516C Cores 34R and 35R, which are estimated to be deposited during mid-Cenomanian based on biostratigraphy. For high-resolution analysis, organic carbon isotope ratio (d13Corg), total organic carbon (TOC), total nitrogen (TN) and C/N ratio were obtained and discussed. Biomarker analysis, focused on specific markers such as alkenones that were interpreted to be related to surface productivity. The following were discussed and concluded.
(1) The d18O variations in sea surface temperature as large as 4°C found by previous study did not have concordant fluctuation with the terrestrial and seafloor environmental changes shown by TOC and d13Corg variations. Land and seafloor were controlled by separate factors.
(2) The variations in d13Corg can be interpreted to be partly related to the redox conditions of the seafloor, rather than being controlled by the mixing ratio of terrestrial and marine in origin.
(3) C37 alkenones derived from haptophytes were recognized. The detection of C37 alkenone with two-unsaturation sites and the absence of that with three-unsaturation sites. These facts suggest that the sea surface temperature at that time may have been higher than the current equatorial water temperature (>28°C) even in the high latitude. Negative correlation of C40 alkenones with d18O of carbonate indicates its potential significance for paleothermometry.