The oceans have become oxygen poor many times throughout Earth's history, and deposited marine sediments called black shales. To understand the essential features of black shales and the marine environments in which they formed, the independent component analysis (ICA), a kind of multivariate statistical analysis, was applied to the integrated dataset of chemical composition of the black shales and blackish-colored muds formed in oxygen-poor marine environments at three different times: during the Permian–Triassic boundary (PTB), Cretaceous oceanic anoxic events (OAEs), and in late Cenozoic. As a result, four independent components (ICs) related to the enrichment of industrially critical metals were extracted. The development of chemoclines (IC1) was a common phenomenon during all studied periods, whereas other components were characteristic of specific environments: increased primary productivity (IC3) was characteristic of OAE 1a samples about 120 million years ago, the formation and preservation of pyrite (IC4) was facilitated at the PTB about 252 million years ago, and an abundance of organic matter (IC2) characterized both the PTB and Cretaceous OAEs. This study demonstrated that the combination of extracted IC can express the characteristics of the chemical composition of black shales. These findings on the diversity of the metal concentrations in black shales will provide highly important insights not only into marine environmental changes but also into the discovery of new types of resources for industrially critical metals.
Papers
Journal: Paleoceanography and Paleoclimatology
Title: Geochemical variations in sedimentary records of oxygen-depleted marine environments in representative geological periods: New perspectives from an independent component analysis
Authors: Moei Yano, Kazutaka Yasukawa, Kentaro Nakamura, Junichiro Kuroda, Minoru Ikehara, Hikaru Iwamori, Yasuhiro Kato
DOI: 10.1029/2024PA005004