Epicontinental seas were important features of the paleogeographic landscape during the Cretaceous; however, the role they played as sinks of organic carbon is still poorly understood. The La Luna Formation (Albian-Coniacian) is a series of organic-rich limestones deposited in northwestern South America on an epicontinental sea (the La Luna Sea). This formation offers a forty-million-year continuous record of environmental change characterized by periods of oceanic anoxia in an epicontinental sea. The La Luna Sea, may have played an important role –although so far unexplored– in carbon cycling through the ocean during the Cretaceous, specifically during short-term, global-scale disruptions in the carbon cycle known as oceanic anoxic events (OAEs). To evaluate the role of the La Luna Sea in global carbon cycle perturbations, we conducted a detailed lithological and chemostratigraphic analysis of two stratigraphic sections from the Upper Magdalena Basin of Colombia, both of which encompass the Oceanic Anoxic Event 2 (OAE2) at the Cenomanian–Turonian boundary. Compared to deposits in the modern ocean, the La Luna Formation has high total organic carbon (TOC) before, during, and after OAE2. Foraminifera and nannoplankton assemblages also imply a stressed upper water column during OAE2. Geochemical and paleontological evidence suggests that the sediment-water interface was anoxic across the late Cenomanian and early Turonian. Strata deposited just after OAE2, however, contain inoceramid bivalves, consistent with short-lived re‑oxygenation of the benthic layer. Estimates of primary productivity, the covariation of Mo and U enrichment factors, and relations between Cd, Mo, Co, and Mn also reveal that the La Luna Sea was biogeochemically similar to the modern Cariaco Basin.

Despite high concentrations of organic carbon found in the La Luna Formation, mass-accumulation rates of organic carbon are low, a finding that can be explained by a reduction in the accumulation rate of sediments caused by the peak of sea-level transgression that took place at the Cenomanian–Turonian transition. Based on the areal extent of the La Luna Sea and mass-accumulation rates of organic carbon, 1.7 Eg of C were removed from the ocean over 500 ky and deposited in the La Luna Sea. Interestingly, although the La Luna Sea was one-third the size of the Western Interior Seaway (WIS), the amount of organic carbon buried in the WIS during OAE2 was similar (1.4 Eg of C). In these two epicontinental seas, 3.1 Eg of C were removed from the ocean during OAE2, accounting only for 3.4% of the total C needed to cause a perturbation of the carbon cycle similar to that observed during OAE2. The low amount of organic carbon buried in the La Luna Sea and the WIS suggests that neither of these inland seas were responsible for the efficient removal of organic carbon from the ocean during OAE2. This conclusion challenges the explanation that epicontinental seas were major sinks of organic carbon—and therefore they did not play a significant role in the carbon cycle during the Mesozoic OAEs and other disruptions of the carbon cycle in Earth's history.

上陆大陆海是白垩纪古地理景观的重要特征。然而，人们对它们作为有机碳汇的作用仍然知之甚少。La Luna地层（Albian-Coniacian）是一系列富含有机质的石灰岩，沉积在南美洲西北部的陆上大陆海（La Luna海）上。这种形成提供了四千万年连续的环境变化记录，其特征是上陆海域缺氧。在白垩纪期间，特别是在称为全球性缺氧事件（OAEs）的碳循环的短期，全球规模破坏期间，拉鲁纳海可能在重要的碳循环中发挥了重要作用（尽管至今尚未探索）。要评估拉鲁纳海在全球碳循环扰动中的作用，我们对来自哥伦比亚上马格达莱纳盆地的两个地层进行了详细的岩性和化学地层学分析，这两个地层都包含了西诺曼尼亚–土伦边界的海洋缺氧事件2（OAE2）。与现代海洋中的沉积相比，La Luna组在OAE2之前，期间和之后的总有机碳（TOC）高。有孔虫和南浮游生物的组合也暗示了OAE2期间上部水柱受压。地球化学和古生物学证据表明，沉积物-水界面在整个西诺曼期和突厥早期都缺氧。然而，刚好在OAE2之后沉积的地层中含有卵虫卵双壳类动物，这与底栖层的短暂再充氧相一致。估算初级生产力，Mo和U富集因子的协变以及Cd，Mo，

尽管在拉鲁纳组中发现了高浓度的有机碳，但有机碳的质量积累率仍然很低，这一发现可以用发生的海平面越过高峰导致的沉积物积累率降低来解释。在Cenomanian-Turonian过渡时期。根据拉鲁纳海的面积范围和有机碳的质量累积率，在超过500 ky的海中从海洋中去除了1.7 Eg C，并将其沉积在拉鲁纳海中。有趣的是，尽管拉鲁纳海只有西方内陆海道（WIS）的三分之一，但在OAE2期间埋在WIS中的有机碳量却差不多（1.4 Eg C）。在这两个上陆大陆海中，OAE2期间从海洋中去除了3.1 Eg的C，仅占3。引起碳循环扰动所需的总碳的4％，类似于在OAE2中观察到的。埋藏在拉鲁纳海和WIS中的有机碳数量很少，这表明这些内陆海域都不是在OAE2期间有效从海洋中去除有机碳的原因。这一结论对以下观点提出了质疑，即上陆大陆海是有机碳的主要汇源，因此，它们在中生代OAEs的碳循环以及地球历史上其他碳循环的破坏中没有发挥重要作用。