Periodic components in the diversity of calcareous plankton and geological events over the past 230 Myr

Abstract

We performed statistical analysis on high-resolution records of the diversity of calcareous plankton (planktonic foraminifera and calcareous nannoplankton), and on records of global sea level, marine isotopes ( δ 18O, δ 13C, 87Sr/ 86Sr), large igneous province (LIP) eruptions, and dated impact craters over the last 230 Myr. Results of Continuous Wavelet Analysis (CWT), Fast Fourier Transform (FFT) spectral analysis and cross-spectral analysis indicate that the records of diversity of calcareous nannoplankton (CN) and planktonic foraminifera (PF) and all of the geologic time series tested show similar dominant 25–33 Myr cycles. Based on the statistical results, best-fit stationary-periodic models for PF and CN evolutionary records can be constructed (with t=time in Myr): CN diversity=9.5 sin(2 π( t−7.5 Myr)/29 Myr)+4.8 sin(2 π( t−4 Myr)/15.3 Myr), and PF diversity=7.6 sin(2 π( t−12 Myr)/26 Myr)+3 sin(2 πt/9.2 Myr). These periodic models describe major patterns in the diversity history, such as: (1) a sawtooth-shaped 29-Myr cycle for calcareous nannoplankton diversity, with gradual increases and abrupt decreases in diversity; (2) plateau-shaped ∼26-Myr cycles in the planktonic foraminiferal record, with abrupt diversity increases and decreases; and (3) the presence of ∼15.3- and 9.2-Myr periodic components that modify the shapes of the 26- to 29-Myr cycles. Except for the synchronous decreases in diversity of PF and CN at 65 and ∼34 Ma, the diversity extrema for the two planktonic groups have been on average ∼2 to 3 Myr out of phase. In the ∼30-Myr-cycle band, CN diversity increased with sea-level rise and increased paleotemperatures, whereas PF diversity was, in general, greater during times of lower sea levels. Diversity of PF and CN was reduced at times of major LIP eruptions and large impacts that follow ∼15 or 30 Myr periodicities. These results suggest that the diversity of calcareous plankton since their appearance in the early Mesozoic has been modulated by long-term cyclical changes in global environmental conditions and by periodic large volcanic and impact events. The pacemaker, or pacemakers, for these cycles may be astrophysical, geophysical or some combination of the two.