Reconstructing Eocene Eastern Indian Ocean Dynamics Using Ocean-Drilling Stratigraphic Records
Ke Xu, David De Vleeschouwer, Maximilian Vahlenkamp, Renchao Yang, and Honghan Chen
Summarized by Olivia Cashimere, who is pursuing her Masters in Geology at Binghamton University. She is currently in her first year, and after graduation would like to work at a research museum. When she is not studying she enjoys hiking, traveling, and a variety of art mediums.
What data were used: This study focuses on two ocean drill hole archives, Ocean Drilling Program Sites 762C and U1514, located within the Eastern Indian Ocean. This study is concentrating on a 22 million year time span within the Eocene Epoch. This time period was leading up to a transition from a greenhouse to ice house climate conditions during the Cenozoic. During this time not much continental ice is seen around the globe, so not many ice related positive feedbacks are seen throughout the Eocene however, strong correlation is found between Milankovitch cycles and the climate changes. This study also uses previous studies on paleomagnetism and biostratigraphy to determine ages, and to check for ambiguity within the record.
Methods: This data collected from ODP Sites 762C and U1514 was applied to orbital scale dynamics using existing sedimentary sequences with biostratigraphy, radio-isotope dating, and magnetostratigraphy. Then stratigraphic interpretation from Site 762C is combined with an existing age depth model from Site U1514 to create a high resolution timescale for the Eocene. Downhole wireline logging with a natural gamma radiation spectrometer was also used to provide elemental data of potassium, thorium, and uranium. These help determine mineral composition, humid vs. dry environments, and astronomically forced climate signals. Using the log10 (Th/K) data a time series analysis was developed, omitting any gaps from poorly recovered core in the data. Previous studies done on Hole 762C provides data and analysis on the magnetostratigraphic record and calcareous nannofossil biostratigraphy. This data was combined to create a reconstruction of the Eocene timescale.
Results: The log10 (Th/K) analysis variability is found in cyclic patterns that roughly match with age depth, with an important note that there are four major gaps found in core recovery. Spectral analysis and depth-series provides sufficient data that sediment accumulation is steady, and power spectrum analysis identifies time series, prominent cycles, and peak frequencies exceeding 99% confidence level. Using the biostratigraphic markers previously found, the orbital tuning for Site 762C, correlated with a 405 kyr eccentricity cycle, and the paleomagnetic data was revamped to match boundaries, however, because of poor core recovery much of this data is still ambiguous and will require further studies. However with this record it reduced the number of gaps from six to four. This allowed for a supported hypothesis overall, and the combined research created an Eocene astronomical timescale that has correlated collected data across various other research methods.
Why is this study important? This study is focusing on key forcing factors that could have changed the climate dramatically during the Eocene. During this time period it is believed that there was very little continental ice across the globe, so any positive feedback from these ice sheets would be mostly nonexistent. However, we must have forcing factors that effect the environment. This study is theorizing on the possibility of astronomical forcing in deep-water circulation in the western North Atlantic. This study also identifies obliquity as the driver of Eocene climate conditions. This can be applied to current day climate systems to theorize about the current global climate warming and its effects of the planet.
The big picture: The obliquity of Earth’s rational axis plays an important role in the deep water circulation and the movement of sediment supply. Low obliquity can be found to coincide with the cooling of ocean temperatures, and high obliquity with its warming. This idea can be used throughout may areas of study to increase our knowledge of how the Earth’s rotation changes our climate systems, and how sediments have been transported through ocean systems in the past.
Citation: Xu, K., De Vleeschouwer, D., Vahlenkamp, M., Yang, R., & Chen, H. (2021). Reconstructing Eocene Eastern Indian Ocean Dynamics using ocean‐drilling stratigraphic records. Paleoceanography and Paleoclimatology, 36(2). https://doi.org/10.1029/2020pa004116