An update for understanding geological time

Earth’s orbit varies due to gravitational interactions within the solar system, leading to cyclical changes in the distribution of incoming solar radiation. This astronomical forcing drives long-term climate variability, which in turn influences sediment production, transport, and accumulation. In the sedimentary record, these processes may be expressed as rhythmic lithological alternations, such as limestone–marl alternations (LMAs), that can potentially be linked to orbital climate cycles. Cyclostratigraphy aims to identify and interpret such cyclic patterns in sedimentary successions to estimate sedimentation rates and reconstruct geological time. However, diagenetic processes can modify, obscure, or even generate cyclic patterns independent of external environmental forcing.

A method to assess the extent of diagenetic alteration is the vector length method (Nohl et al., 2021), which quantifies differences in elemental ratios between lithological couplets. This approach can be transferred to (1) test for diagenetic overprint, and (2) assess variability in accumulation rates or sediment condensation.

IODP Site U1410 is characterised by rhythmic alternations of nannofossil ooze and clay-rich nannofossil ooze, which have previously been interpreted as dilution cycles. However, observed changes in Al/Ti ratios between the two lithologies indicate that the terrigenous input varies not only in amount but also in composition and source, adding further nuance. By comparing the results with common cyclostratigraphic analyses, we aim to assess the reliability of astronomically derived age models and improve estimates of the temporal resolution preserved in the geological record.