Revisiting stylolites as a gage of overburden pressure – insights from fractal analysis

Stylolites are ubiquitous structures generated by pressure solution primarily found in limestones. They and have been used as indicator for maximum stress a rock has suffered. This is commonly done by characterizing the fractal dimensions of stylolites. The current canon is the expectation from the theory that stylolites form through two physical pressure-driven regimes: low-frequency and higher-energetic - dominated by elastic forces and high-frequency lower-energetic dominated by surface tension. The so-called characteristic length separates both regimes, analytically marked by a kink in the power spectrum, which relates the energy contributions to the frequency.

However, determining this kink is not straightforward, and requires additional assumptions. We present a data set of stylolites recovered from a drill hole in the Alpine foreland basin. We mapped stylolites from different depths at sub-mm resolution semi-automatically and analyzed them using new methods of fractal analysis.

Excitingly, our preliminary studies did not identify the expected kink’s position from several different images of probes of drill cores, despite satisfactory reliability of laboratory preparation. Standard methods such as power spectral density, averaging wavelet coefficients, RMS, min/max, and rescaled range-based approaches revealed variations in their results, generally without evidence for a kink in the corresponding graphs. Implementing more recently developed methods such as adaptive fractal analysis could not improve the results. This finding challenges the classic interpretation of fractal characteristics of stylolites.