Astronomical Forcing–Driven Nonlinear Organic Carbon Burial and Lithofacies Evolution: Insights From Lacustrine Shale of the Funing Formation, Subei Basin, Eastern China

ABSTRACT

Lacustrine organic carbon burial plays a critical role in the Earth's carbon cycle, yet its response mechanisms to multi‐scale astronomical forcing remain poorly understood, particularly in mid‐ to low‐latitude regions. This study focuses on the second member of the Funing Formation (E ₁ f ₂ ) in Well QY‐1, Qintong Sag, Subei Basin, eastern China, covering a depth interval of 3680–4060 m and an age range of 52.79–57.21 Ma. The interval was deposited in a mid– to low‐latitude setting and is characterised by thick organic‐rich shale successions. Based on these considerations, lithofacies subdivision and cyclostratigraphic analyses were therefore conducted to investigate the mechanisms by which astronomical orbital forcing controlled paleoclimate evolution, organic carbon burial and facies development. Spectral analysis identifies prominent orbital signals, including long eccentricity (405 kyr), obliquity (~40 kyr), precession (~20 kyr) and ~173 kyr cycle. Based on variations in sedimentation rate, E ₁ f ₂ is subdivided into three subintervals (Intervals I–III). Interval II is characterised by relatively high sedimentation rates and persistent long‐eccentricity and obliquity signals, both of which modulate the total organic carbon (TOC) burial. Notably, the ~173‐kyr cycle is prominently expressed only in the TOC record and is absent from the GR record, which may reflect a nonlinear modulation of orbital forcing during organic carbon burial. We infer that a sedimentary threshold existed in the lacustrine depositional system, which played a regulating role in organic carbon burial and further amplified the ~173‐kyr signal recorded in the TOC record. Based on the nonlinear response of organic carbon burial, as well as the organic matter abundance and structural characteristics of different lithofacies, we propose an astronomically forced lithofacies evolution model for lacustrine shale. This model provides a theoretical framework for lithofacies identification and evaluation of the most favourable organic‐rich intervals in lacustrine shale successions.