Changing environments can change the rate of formation of layers in sedimentary rocks, leading to inaccurate time estimates

Layers of sedimentary rock are often studied to reconstruct Earth’s history. But rocks aren’t always the most reliable historians. New research shows how—and how quickly—sediment accumulation can dramatically affect ecological conditions, confounding scientists trying to estimate the length of Earth’s past.

Barefoot et al. Sedimentation rates and patterns were studied by simulating a natural system using an experimental basin. The researchers simulated floods of various amplitudes and measured how these floods affected sediment accumulation.

Low-amplitude floods distributed debris in patterns marked by ruggedness, with several localized ridges and hills separated by valleys, the researchers found. That means that when the flood rose in a high-magnitude event, there were plenty of topographic nooks and crannies to capture debris over a wide area, allowing it to build up in a thick, smooth layer. When the reverse transition occurred and low-amplitude flooding occurred again, there were only localized rough patches to trap debris, and the resulting layers were thin.

These depositional differences—localized versus widespread, thick versus thin—become obscured when scientists later look at sections of the resulting sedimentary stratigraphy, leading to misinterpretation of the timing and timing of deposition of given layers. Scientists report that during a transition to a high-amplitude flood regime, for example, assuming a linear sediment accumulation rate can overestimate deposition duration by up to 30%.

Processes and feedbacks other than those studied here affect how sediments are deposited and preserved. But, the researchers say, the work is a step toward more accurately estimating time scales gleaned from stratigraphic records.

The findings are published in the journal Geophysical Research Letters.