Crockford Proterozoic Triple Oxygen Isotopes

Triple oxygen isotope compositions of sedimentary sulfate (∆’17O) have been applied as a tracer of past primary productivity, pO2 and pCO2. However, large intraformational variability of ∆’17O signatures and debate surrounding how they are produced and eventually preserved has limited the understanding of this important geochemical record. Here we explore depositional controls on ∆’17O signatures of mid-Proterozoic (≈2.0-1.0 Ga) sulfates. We identify a clear depositional control on the magnitude of preserved ∆’17O sulfate signatures, with Proterozoic terrestrial environments preserving the most negative and variable signatures and marine environments displaying values near modern marine sulfate with less overall variability. Our results strongly suggest that local depositional settings influence the magnitude of preserved ∆’17O signals, and the processes within those environments drive much of the observed intraformational variability. Finally, this analysis suggests that ∆’17O signatures in concert with sedimentological observations may offer a powerful tool to identify basin restriction and non-marine settings throughout the geologic record.

沉积硫酸盐的三氧同位素组成（Δ'¹⁷O）已被用作重建古初级生产力、大气氧分压（pO₂）与大气二氧化碳分压（pCO₂）的地球化学示踪剂。然而，Δ'¹⁷O同位素信号存在显著的层内变异性，且学界围绕其形成机制与最终保存过程仍存在诸多争议，这极大限制了人们对这一重要地球化学记录的认知。本研究针对中元古代（约20亿~10亿年）硫酸盐的Δ'¹⁷O同位素信号的沉积控制因素展开系统性探讨。研究明确了沉积作用对沉积硫酸盐Δ'¹⁷O信号强度的显著调控作用：中元古代陆相环境中保存的Δ'¹⁷O信号偏负程度最高、变异性最强；而海相环境的Δ'¹⁷O值则接近现代海相硫酸盐，整体变异性更低。本研究结果有力表明，局部沉积环境会直接调控沉积硫酸盐Δ'¹⁷O信号的强度，而各环境内部的地球化学过程正是造成观测到的层内变异性的核心驱动因素。最后，本分析证实，将Δ'¹⁷O同位素信号与沉积学观测数据相结合，可作为一种高效的研究手段，用于在全球地质记录中识别盆地封闭环境与非海相沉积环境。