Astrochronology for the oldest Cambrian trilobites in Moroccan West Gondwana

The lower Cambrian successions of Southern Morocco (West Gondwana) feature some of the oldest trilobites and archaeocyaths fossil remains in the world, as well as some of the largest carbon isotope excursions of the Phanerozoic. Combined with multiple state-of-the-art U-Pb radio-isotopic constraints, these sections are key references for lower Cambrian stratigraphy. We suggest that some of the regularly alternating lithological sequences, which show various orders of nested cyclicity, carry a signal of astronomical climate forcing. In agreement with a U-Pb Bayesian age model, the primary lithological alternation corresponds with the precession astronomical cycle while clear amplitude modulation patterns reflect a short-term eccentricity imprint. Both small- and large-scale features are laterally continuous at great distances. Changes in lithology may have been primary controlled by changes in terrigenous input. This integrated astrochronological age model has the potential to result in unprecedented early Cambrian timescales for major paleoenvironmental changes like the appearance of key fossils and large carbon isotope excursions. Often, lower Cambrian and Precambrian strata lack classical stratigraphical tools like good index fossils or magnetostratigraphy. In comparison with younger strata, the combined use of high-quality radio-isotopic dating and high-precision astrochronology might be even more crucial to disentangle important events in the early evolution of life and climate on our planet.