Cyclostratigraphy

Cyclostratigraphy is the branch of stratigraphy that uses the periodicities embedded in sedimentary records, driven by astronomical forcing, to construct time scales for geological sequences. It often overlaps with astrochronology, which seeks to convert these orbital-driven cycles into absolute ages.

Principles and scope: Sedimentary sequences can exhibit regular cycles in sedimentation rate and composition linked to Milankovitch cycles—precession (about 19–23 thousand years), obliquity (about 41 thousand years), and eccentricity (about 100 thousand and 400 thousand years). By identifying these signals in rock records and aligning them with orbital solutions, scientists build a tunable time framework for the succession.

Methods and data: Researchers use high-resolution records from deep-sea sediments, carbonate platforms, and lacustrine deposits, including lithology, magnetic susceptibility, isotopic proxies (δ18O, δ13C), color, and fossil content. Spectral analysis (Fourier, wavelet, multitaper) detects periodicities, which are then tuned to the known orbital frequencies. The resulting astrochronostratigraphic framework is cross-checked with magnetostratigraphy and available radiometric or biostratigraphic constraints.

Limitations and considerations: Signals may be altered by diagenesis, hiatuses, variable sedimentation rates, or non-orbital forcings. Orbital solutions are not perfectly stationary through long timescales, which can introduce uncertainties. Robust cyclostratigraphic construction requires careful testing, independent age controls, and awareness of potential circular reasoning.

Applications and significance: Cyclostratigraphy helps calibrate the geological time scale, correlate stratigraphic records across basins, and reconstruct past climate and sea-level cycles. It is especially valuable for dating sedimentary sequences in intervals with continuous records and limited radiometric data.

See also:

- Astrochronology

- Milankovitch cycles

- Magnetostratigraphy

- Geochronology