Over millions of years, slow changes in Earth’s orbit around the Sun have altered the planet’s climate and left clear traces in the rocks beneath our feet. Now, new research suggests that these ancient cycles may also explain why some shale layers are rich in organic material, while others are not.
In the recent research published in the Journal of Palaeogeography, scientists led by Professor Xian Benzhong from China University of Petroleum studied Jurassic-age lake sediments from China’s Sichuan Basin. They found that slow, repetitive changes in Earth’s orbit influenced where organic-rich shale formed. The study connects planetary cycles to small differences in sediment and organic matter, which are important for modern shale oil exploration.
A Persistent Problem in Shale Exploration
Shale oil is now a major part of the world’s energy supply, but it is still hard to predict where the best shale layers are found. Even within a single formation, the amount of organic material can change quickly from one layer to the next. Some layers produce oil, while others do not.
Climate and other factors can help explain some of these differences, although such environmental influences often provide little detail. Most models describe general patterns, such as wet or dry periods and changes in lake level, but do not show how those conditions shift over time. This lack of detail has made it hard to rely on climate information for drilling decisions.
Orbital Cycles as Climate Drivers
The new research focuses on mudstones that were deposited roughly 170 million years ago within a vast ancient lake. Rather than treating the formation as a single, gradually accumulating layer, the scientists treated it as a record shaped by a series of repeating external influences over time.
Earth’s orbit changes slowly over time. Over hundreds of thousands of years, the planet’s path around the Sun either becomes more circular or more stretched out. These shifts change how sunlight reaches the planet in different seasons, which in turn affects climate patterns.
The researchers wanted to find out whether these orbital changes left a measurable imprint in lake sediments. They also set out to determine whether those imprints influenced the accumulation of organic material.
A Jurassic Climate Archive
The team analyzed borehole data from several wells using natural gamma-ray logs, core observations, and geochemical measurements. Rather than relying on a single dataset, they searched for repeating patterns across datasets that could be matched in time.
The patterns they found were extremely consistent. The sediments showed cycles that matched known changes in Earth’s orbital eccentricity, including a long-term signal that repeats every 405,000 years. With this signal, the researchers constructed a detailed timeline of how the sediments formed. This timeline allowed the team to directly compare climate conditions with changes in sediment type and organic material.
Orbits Shape Oil-Rich Shales
The results showed that when Earth’s orbit was more eccentric, the water levels of the lake were higher. As a result, more nutrients flowed in, biological activity increased, and fine sediments settled in the deeper parts of the lake. These layers preserved organic material well. Today, they match up with the most oil-rich shale in the formation.
Periods with lower eccentricity were different. Drier conditions meant less runoff, lower lake levels, and more coarse sediment. Sometimes heavy sediment flows brought sand into the deeper basin, interrupting the buildup of organic material.
A Planetary Perspective on Earth’s Resources
If organic-rich shale forms during certain climate periods, then cyclostratigraphic analysis can help focus the search for the best layers. Rather than seeing shale formations as random, exploration teams might be able to spot repeating patterns linked to outside forces.
The study also questions the idea that deep lake environments continuously build up sediment. Even in the basin’s center, the researchers found gaps and interruptions. These features can affect how reservoirs connect across the area.
As energy systems face pressure to become more efficient, knowing where resources are concentrated is crucial. The recent research demonstrates that some of those patterns can be predicted by the slow movements of the solar system, and in this way, serves as a reminder that the forces shaping Earth’s resources often have more distant origins.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds a Master of Business Administration, a Bachelor of Science in Business Administration, and a Data Analytics certification. His work combines analytical training with a focus on emerging science, aerospace, and astronomical research.