Milankovitch cycles in Upper Jurassic and Lower Cretaceous radiolarites of the equatorial Pacific: spectral analysis and sedimentation rate curves

Abstract

Cycles of variable concentration of radiolarians and clay, and associated changes in degree of silicification were apparent in the geophysical logs, especially in the γ-ray log signal using a 40-m sliding window. The dominant spectral peaks maintain the same relative ratios in frequency as the 413-k.y., 123-k.y., and 95-k.y. Milankovitch periods of eccentricity. Two sharp discontinuities in sedimentation rate were inferred: 1) a Callovian/Oxfordian boundary hiatus, and 2) a discontinuity of probable late Tithonian-early Berriasian age. Eccentricity cycles identified in the γ-ray signal were matched to corresponding features on the Formation MicroScanner high-resolution imagery of clay content and degree of silicification. -from Authors