Fig. 2: Quarter-precessional cycles in Cretaceous terrestrial and marine records.
From: Precession-induced millennial climate cycles in greenhouse Cretaceous
A–C Grayscale, log (Ca/Ti), and Rb/Sr datasets from the SK2 borehole with their ~95.2-kyr (0.0105 ± 0.0035 cycle/kyr), ~22-kyr (0.0455 ± 0.0095 cycle/kyr), and ~4–5-kyr (0.215 ± 0.055 cycle/kyr) filters. D The astronomically-tuned L* datasets (blue) based on TimeOpt chronology (Fig. S4) and anchoring to the magnetostratigraphic age at 1145.132 m (80.702 Ma), with precessional filters (0.054 ± 0.011 cycles/kyr). E The evolutive power spectra of L* using the EHA method62, with ~405-kyr filter of tuned L*. F The selected intervals of tuned L* showing quadripartite structure, in which every precession cycle (0.054 ± 0.011 cycles/kyr) includes two semi-precessional (0.1 ± 0.02 cycle/kyr) and four quarter-precessional (0.215 ± 0.055 cycle/kyr) cycles. The quarter-precessional cycles in L* are most prominent at peaks of the 405-kyr filter of L*, indicating an intermodulation relationship between quarter-precessional cycles and long eccentricity.
