近日，美国新罕布什尔大学William C. Clyde团队研究了古沉积物碳酸盐δ¹³C值中保存的光合碳循环信号。相关论文发表在2025年8月6日出版的《地质学》杂志上。

现今形成的凝块有机沉积物保存了碳酸盐碳同位素（δ¹³C_carb）值，这表明光合作用改变了当地溶解的无机碳库的δ¹³C值，从而形成了δ¹³C_carb值为1‰，与环境湖水平衡沉淀的碳酸盐矿物比预期值高6‰。

为了验证这些信号是否被保存在地质记录中，研究组分析了白垩纪至始新世羊口组（美国内华达州）的沉淀形成物的δ¹³C_carb值。 对凝块成分（解释为反映光合作用影响的降水）和相邻的碳酸盐基质（解释为反映非生物降水）进行了织物特异性分析，发现凝块成分的δ¹³C_carb值始终被抵消到比相邻基质更高的值。沉积物与基质之间的平均偏移量（Δ¹³C）为+2.77‰（±0.94,2 s.e）。

这些Δ¹³C值与光合作用驱动的日碳循环模型的预测一致。模拟的Δ¹³C值也与有沉积物形成的现代湖泊中记录的Δ¹³C值相匹配。研究组认为Sheep Pass组Δ¹³C值保留了与溶解无机碳库的本地和外部影响相关的信号。织物信息采样可以解开这两个信号，除了确定光合作用的生物特征外，还可以从微生物岩档案中获得更精确的化学地层学。

附：英文原文

Title: Photosynthetic carbon cycling signal preserved in carbonate δ13C values of ancient thrombolites

Author: Juliana Olsen-Valdez, Cedric J. Hagen, Sarah J. Widlansky, Elizabeth J. Trower, Kathryn E. Snell, William C. Clyde

Issue&Volume: 2025-08-06

Abstract: Thrombolites—clotted organo-sedimentary deposits—forming today preserve carbonate carbon isotope (δ13Ccarb) values that suggest that photosynthesis shifts the δ13C value of the local dissolved inorganic carbon pool, resulting in carbonate minerals with δ13Ccarb values 1‰6‰ higher than that expected for carbonate minerals precipitated in equilibrium with ambient lake water. To test whether these signals are preserved in the geologic record, we analyzed the δ13Ccarb values of thrombolites from the Cretaceous to Eocene Sheep Pass Formation (Nevada, USA). We performed fabric-specific analyses of both the clot component (interpreted to reflect photosynthetically influenced precipitation) and adjacent matrix carbonate (interpreted to reflect abiotic precipitation) and find that the δ13Ccarb values of clot components are consistently offset to higher values than adjacent matrix. The mean offset (Δ13C) between the clots and matrix was +2.77‰ (±0.94, 2 s.e.). These Δ13C values are consistent with predictions by a model of diurnal carbon cycling driven by photosynthesis. Modeled Δ13C values also match the documented Δ13C values in modern lakes with thrombolites. We interpret that Sheep Pass Formation Δ13C values preserve signals related to both local and external influences on the dissolved inorganic carbon pool. Fabric-informed sampling can disentangle these two signals, allowing for more robust chemostratigraphy from microbialite archives in addition to identification of a biosignature of photosynthesis.

DOI: 10.1130/G53716.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G53716.1/660249/Photosynthetic-carbon-cycling-signal-preserved-inredirectedFrom=fulltext