Orbital pacing and secular evolution of the Early Jurassic carbon cycle
Marisa Storm, Stephen P. Hesselbo, Hugh C. Jenkyns, Micha Ruhl, Clemens V. Ullmann, Weimu Xu, Melanie J. Leng, James B. Riding, Olga Gorbanenko
Abstract
Significance Cyclic variations in Earth’s orbit drive periodic changes in the ocean–atmosphere system at a time scale of tens to hundreds of thousands of years. The Mochras δ 13 C TOC record illustrates the continued impact of long-eccentricity (405-ky) orbital forcing on the carbon cycle over at least ∼18 My of Early Jurassic time and emphasizes orbital forcing as a driving mechanism behind medium-amplitude δ 13 C fluctuations superimposed on larger-scale trends that are driven by other variables such as tectonically determined paleogeography and eruption of large igneous provinces. The dataset provides a framework for distinguishing between internal Earth processes and solar-system dynamics as the driving mechanism for Early Jurassic δ 13 C fluctuations and provides an astronomical time scale for the Sinemurian Stage.