Publication

Throughout the Phanerozoic, the oceans repeatedly became oxygen depleted and deposited marine sediments called black shales. The mechanisms responsible for the compositional variability of black shales deposited at different times and places, however, are not yet fully understood. Here, we performed an independent component analysis (ICA) to extract essential geochemical features of sedimentary records in oxygen-depleted environments. We targeted the bulk chemical compositions of black shales from the Permian–Triassic boundary (PTB) and Cretaceous oceanic anoxic events (OAEs), as well as organic-rich sediments of the late Cenozoic. The ICA results demonstrated that the chemical characteristics of the black shales/sediments could be explained by four key processes/components. The development of chemoclines (IC1) was a common phenomenon during all studied periods, whereas other factors were characteristic of specific environments: increased primary productivity (IC3) was characteristic of OAE 1a samples, the formation and preservation of pyrite (IC4) was facilitated at the PTB, and an abundance of organic matter (IC2) characterized both the PTB and Cretaceous OAEs. Our new data-driven approach demonstrates that geochemical variations in black shales/sediments from different times and places can be explained by a combination of geochemical ICs, and that use of ICs that reflect information about multiple elements can be a novel and broadly applicable mechanism to systematically capture the characteristics of black shales and organic-rich sediments.