On the geological and scientific legacy of petrogenic organic carbon

Abstract

Weathering, erosion, and redeposition of exhumed rock-derived or “petrogenic” organic carbon (OC) co-occurs with the burial of biospheric OC within sediments, modulating atmospheric CO₂ and O₂ over geologic time. Disentangling the geochemical fingerprint of petrogenic OC from biospheric OC in sedimentary organic matter, as well as quantifying the influence of its remineralization and burial on atmospheric CO₂/O₂, has been the focus of numerous observational and geochemical modeling studies. In 1938, Matti Sauramo recognized that petrogenic OC is entrained in a “simple carbon” cycle operating alongside the “complicated” greater rest of the carbon cycle. Sauramo's achievements were preceded by Charles Lyell's thoughts on the subject a century earlier, and by observations of reworked palynomorphs in the modern environment made by palynologists in the 19^th Century. Towards the present, palynologists, organic petrologists, and geochemists have all made key advances, while their impact often did not radiate beyond their respective bodies of literature. This highlights the importance not only of further investigations focused on the continued pursuit of new information, but also on studies of the history of relevant disciplines in order to place new findings in appropriate context. Petrogenic OC cycling has emerged as a key process for constraining global carbon budgets, long-term biogeochemical cycles and associated variations in atmospheric chemistry. While petrogenic OC is now recognized as a significant component of bulk sedimentary OC in modern systems, its cycling throughout Earth's history - including during pivotal episodes such as supercontinent amalgamation and late Proterozoic Snowball Earth events followed by greenhouse conditions - remains largely unexplored.