A Stanford University study challenges expectations of massive sediment deposits resulting from climate change 34 million years ago and instead reveals a global erosion pattern. This discovery provides insight into the impact of climate change on sedimentary systems.
According to widely cited traditional models, cooling and a significant drop in sea level around 34 million years ago should have led to large-scale erosion of the continent and the deposition of huge amounts of sandy material on the ocean floor. After all, this was one of the most severe climate changes on Earth since the extinction of the dinosaurs.
Yet a new Stanford review examining hundreds of studies spanning decades shows that virtually no sediment dating to this transition is found on the margins of all seven continents. The discovery of this global massive gap in the geological record was recently published. Earth Science Reviews.
“The results left us wondering, ‘Where did all that sediment go?'” said study senior author Stefan Graham, the Welton Joseph and Maud L’Anphere Crook Professor at Stanford’s Doerr School of Sustainability. “Answering this question will help us better understand the functioning of sedimentary systems and how climate change affects deep-sea sediments.”
The geological gap offers new insights into processes of sediment deposition and erosion, as well as broader environmental signals resulting from abrupt climate change, and could help researchers better understand the magnitude of modern climate change.
Currently an associate professor, Ph.D. “For the first time, we took a global look at the understudied response of the planet’s largest sediment mass transfer systems during the extreme Eocene-Oligocene transition,” said 2020 lead study author Zach Burton. in earth sciences at Montana State University.
Tim McHarg, assistant professor of Earth and planetary sciences at Stanford, also co-authored the study.
From greenhouse to glaciers
During the Eocene-Oligocene period, Earth experienced profound planetary cooling. Giant ice sheets have appeared in previously ice-free Antarctica, global sea levels have fallen, and land and marine life have been severely destroyed.
Before that, at the start of the Eocene, which lasted about 56 million to 34 million years ago, Earth had the warmest temperatures and highest sea levels since dinosaurs walked the Earth 66 million years ago, according to climate records.
Burton and his colleagues initially focused on studying the effects of early Eocene conditions on deep-sea sedimentary systems. The results of the study have been published Nature Scientific Reports In 2023, he discovered numerous sand deposits in ocean basins along Earth’s continental margins. The research team attributes this increase in sediments mainly to increasing climate and weather conditions that increase soil erosion. Their curiosity wavered, so Burton and his colleagues extended the study to the Late Eocene and Early Oligocene; During this period, the Earth suddenly switched from a “greenhouse” and “greenhouse” climate to the opposite “glacial” climate.
For the new study, researchers meticulously examined scientific and technical literature documenting ancient sedimentary deposits several kilometers below the seafloor, examining studies published more than a century ago in the last decade. The literature included studies of offshore oil and gas drilling, studies of onshore rock outcrops, and even interpretation of seismic data to determine the properties of Eocene-Oligocene sediments. In total, more than 100 geographical locations around the world are included and the boundaries of each continental landmass are drawn.
While the literature review method itself is not new, the scale of the approach made possible by large online databases can be very meaningful, Graham said. “There may be other similar events in the geological past that require closer examination, and to do that, you can start with what we’re doing, which is a truly comprehensive study of the global geological literature,” Graham said. Some questionable periods. in time”.
“The process of re-evaluating, re-examining and re-analyzing decades of published literature is difficult in some cases, but can be very productive,” Burton said. “The method can lead to exciting and unexpected findings, as we were able to do here.”
completely unexpected
As Burton and his colleagues examined the collected data, they became increasingly puzzled by the apparent absence of sedimentary deposits.
“We didn’t see abundant sand deposits like we saw in our Early Eocene warm climate study,” Burton said. “Instead, we found that distinct, widespread erosional unconformities—in other words, gaps in the rock record—developed during the extreme climatic cooling and oceanographic changes of the Eocene-Oligocene.”
Researchers offer several theories as to why this lack of sediment occurs. Strong ocean floor currents driven by water temperature and salinity may have been triggered or exacerbated by significant climate change; potentially eroding the ocean floor and sweeping sediments off the continents. Meanwhile, the mechanisms of continental shelves exposed by falling sea levels may have allowed sediments to bypass nearby sedimentary basins entirely, sending sediments much further out into the ocean floor abyss. More regionally restricted processes, such as glacial erosion around Antarctica, also likely played a role.
Whatever mechanisms were at work, they combined to create similar erosion landscapes in the ocean basins around each continent. This ubiquity points to what researchers call global control; This means profound climate changes are being felt everywhere, from the highest landmasses to the deepest waters.
Therefore, the abrupt climate event at the Eocene and Oligocene boundary and its recently observed significant effects along continental margins may help researchers better understand the global dimensions of modern climate change. Stanford University researchers say human-caused climate change over the past few centuries is now occurring at an alarmingly faster rate, although on a much smaller scale than during the Eocene-Oligocene transition.
“Our findings may help inform us about the radical changes that may occur on the Earth’s surface under conditions of rapid climate change,” Graham said. “The geological past determines the present and especially the future.”
Source: Port Altele
