How Earth's orbit might help us find oil reserves within the planet

Today, science can narrow down potential oil reserves with surprising accuracy — especially when it comes to shale oil, found embedded within sedimentary rock. By studying sediments in China's Sichuan Basin, researchers found that variations in the Earth's orbit can help prospectors better predict where shale oil is most likely to form.

Unlike crude oil, which pools in subterranean reservoirs, shale oil is found within shale rocks. Shale forms from layers of fine sediment deposited in ancient lakes or seas, where low-oxygen conditions allow organic matter to accumulate and, over millions of years, generate oil within the rock.

In the past, shale oil reserves were difficult to pinpoint because scientists lacked a complete understanding of how these rocks formed. The new research fills in a key piece of that puzzle. By combining measurements of different elements in Earth's crust and mantle, rock core observations, and natural gamma-ray data from Jurassic-era lake mudstones, the team reconstructed how environmental conditions changed through time. Those changes, they found, linked up with Milankovitch cycles.

Milankovitch cycles are regularly occurring variations in Earth's orbit and tilt that influence our planet's long-term climate, including the timing of ice ages. The cycle of orbital eccentricity — the stretching and shrinking of Earth's elliptical orbit — operates over hundreds of thousands of years.

The rock record revealed that during periods of high orbital eccentricity, stronger seasonal contrasts produced warmer, wetter conditions that boosted nutrient delivery to lakes. Biological productivity surged, leading to the deposition of finely layered, organic-rich mudstones — the types of rocks most favorable for shale oil.

When eccentricity decreased, the climate shifted toward drier conditions. Lake levels dropped, sediment supply changed, and sand-rich deposits spread across basin slopes and into deeper waters, transported by gravity-driven flows. Together, these alternating wet and dry phases created a predictable stacking pattern of rock types across the basin.

The study also showed that sediment accumulated at an average rate of just over four centimeters per thousand years, allowing researchers to align individual rock layers with specific orbital cycles. Using a newly-developed framework based on this research, scientists can better identify where high-quality shale reservoirs are likely to occur.

It's worth noting that shale oil is not only a fossil fuel, but is also extracted through hydraulic fracturing, or fracking, which carries environmental concerns. Still, until the world fully transitions to renewable energy, oil will remain a major energy source — and combining astronomy with geology is emerging as one of the most powerful tools for finding it.

The team's research was published in the Journal of Paleogeography (Chinese edition) on Sept. 30, 2025.