High-resolution 14C stratigraphy reveals decadal periodicity in stromatolite lamination

Laurane Fogret, Pierre Sansjofre, Sylvain Bernard, Karim Benzerara, Damien Calmels, Stefan Lalonde

Stromatolites constitute amongst the oldest evidence for life on Earth and preserve laminated records throughout most of geological time. However, the timescales represented by their lamination remain poorly constrained. Here, we report the first high-resolution 14C dating combined with Bayesian age-depth modelling for three Holocene stromatolites from contrasting depositional environments. The two samples with stratigraphically coherent age-depth relationships yield time-averaged net accretion rates below 25 μm.yr-1 and mean light-dark couplet durations of ca. 17-24 yr. These results demonstrate that successive laminae couplets do not represent consecutive annual increments. Spectral analyses reveal significant periodicities within the 10-30 yr range in both records, consistent with accretion modulated by decadal environmental forcing. Moreover, a radiocarbon age offset localized across a gypsum-rich interval in the Dead Sea stromatolite reveals a discontinuity, related to a previously dated dry climatic interval, for which laminae-based chronology effectively recovers its age and duration. Two major conclusions stem from this work. First, stromatolite lamination should not be assumed to represent consecutive annual increments. Second, 14C-calibrated stromatolite records can be used to constrain accretion rates, identify cyclic intervals of environmental forcing, and reconstruct past climate events.