Benthic oxygen oases linked to photosynthetic mats have been reported in modern anoxic aquatic systems. Benthic macroalgal blooms were common in stratified, anoxic Neoproterozoic oceans, leading us to hypothesize the existence of benthic oxygen oases at that time. This hypothesis has significant implications regarding the bioavailability of transition metals (e.g., Cu, Zn, Ni, Mo, V) and the distribution of aerobic eukaryotes in these oceans. However, little research has been directed toward testing the benthic oxygen oasis hypothesis in ancient anoxic marine systems. In this contribution, we report on an integrated investigation of iron speciation, trace elements, and carbon–sulfur-δ³⁴S_py for the Tonian Longfengshan Biota-bearing versus non-fossil-bearing shales of the Luotuoling Formation in the Longfengshan section of the Yanshan Basin (North China). Typical marine B/Ga values (6.5–7.3) suggest that the Yanshan Basin was fully marine and well connected with the open ocean. The low Fe_HR/Fe_T ratios of the non-fossiliferous intervals (mean 0.14) suggest oxic water-column conditions during their deposition, and their Fe_HR pool contains significant amounts of pyrite and siderite (up to 44%), implying their formation in underlying reducing sedimentary porewaters. In contrast, the fossil-bearing layers show high and oscillating Fe_HR/Fe_T ratios (mean 0.39; up to 0.51) and systematically low Fe_py/Fe_HR (mean ~0), suggesting dominantly ferruginous water-column conditions with redox oscillation. Furthermore, lack of redox sensitive trace-metal and sulfide enrichments and dominance of the Fe_HR pool by ferric oxide and magnetite (96–100%) indicate substantially oxidative power in the reducing water-column and underlying surface sediments. In combination with coexisting sedimentological and paleontological data, these conflicting and contrasting redox signals can be best interpreted by the development of benthic oxygen oases in deeper reducing waters, regulated by the Neoproterozoic benthic macroalga Longfengshaniaceae most likely in association with microbial/cyanobacterial mats, which contributed the oxidative power in the reducing environments. Our findings provide new insights into early Neoproterozoic oceanic redox conditions, iron cycling and the evolution of early aerobic eukaryotes, including animals.

在现代缺氧水生系统中已经报道了与光合垫相连的底氧绿洲。在分层，缺氧的新元古代海洋中常见底栖大型藻类水华，使我们推测当时存在底栖绿洲绿洲。该假设对过渡金属（例如，铜，锌，镍，钼，钒）的生物利用度以及这些海洋中好氧真核生物的分布具有重要意义。但是，很少有研究针对在古代缺氧海洋系统中测试底栖绿洲假设。在这方面的贡献，我们对铁形态，微量元素和碳-硫δ的综合调查报告³⁴小号_PY燕山盆地（华北）龙凤山段罗托岭组的隆隆山生物区系与非化石页岩对比。典型的海洋B / Ga值（6.5-7.3）表明燕山盆地是完全海洋的，并且与远洋有良好的联系。非化石区间的Fe _HR / Fe _T比值低（平均值为0.14）表明沉积过程中存在有氧水柱条件，并且它们的Fe _HR池中含有大量的黄铁矿和菱铁矿（高达44％），表明它们形成了在减少沉积的孔隙水中。相反，含化石层显示出高的和振荡的Fe _HR / Fe _T比（平均值为0.39；最高为0.51）和系统地较低的Fe_py / Fe _HR（平均值_〜0），表明主要是铁质水柱条件，具有氧化还原振荡。此外，缺乏氧化还原敏感的痕量金属和硫化物富集以及三氧化二铁和磁铁矿（96-100％）对Fe _HR池的支配地位表明在还原的水柱和下层表面沉积物中具有实质的氧化能力。结合共存的沉积学和古生物学数据，这些相互矛盾和相反的氧化还原信号可以通过在新元古代底栖大型藻类龙凤山科的调控下，在深层还原水中的底栖氧气绿洲的发展得到最好的解释。最有可能与微生物/蓝细菌垫有关，它们在还原性环境中贡献了氧化能力。我们的发现为新元古代早期海洋氧化还原条件，铁循环以及包括动物在内的早期有氧真核生物的进化提供了新的见识。