The direct dating of rock paintings is not always possible due to the lack of organic carbon compounds in pigments, or because sampling from a heritage site is often restricted. To overcome these limitations, dating laboratories have to develop new approaches. In this study, we consider sampling calcium oxalate crusts covering the painted artworks as a way to indirectly date the rock art. This stratigraphic approach includes isolating and extracting pure oxalate from the crusts. The approach was tested on natural bulk accretions collected in the open-air sites of Erongo Mountains in Namibia. The accretions were separated into two phases (pure oxalate and the remaining residues) with a special pretreatment. This process removes carbonates through acidification (HCl 6N) and dissolves the oxalate into the supernatant, leaving the minerals and windblown organic compounds in the residue. The efficiency of the separation was checked on the two phases by FTIR analyses and by 14C dating and showed that pure oxalate powders were indeed obtained. AMS radiocarbon results of various accretions on the same art panels provided ages from modern periods to 2410 ± 35 BP. From these first results, more targeted sampling campaigns can be considered to provide a terminus ante quem for the rock art.

中文翻译：

---

草酸钙放射性碳测年：纳米比亚埃龙戈山装饰露天洞穴的岩石艺术迄今为止的初步测试

由于颜料中缺乏有机碳化合物，或者因为从遗产地取样通常受到限制，岩画的直接测年并不总是可能的。为了克服这些限制，约会实验室必须开发新的方法。在这项研究中，我们考虑对覆盖绘画艺术品的草酸钙结壳进行采样，以此作为间接确定岩石艺术年代的一种方式。这种地层学方法包括从地壳中分离和提取纯草酸盐。该方法在纳米比亚 Erongo 山脉露天场地收集的天然堆积物上进行了测试。通过特殊的预处理将附着物分成两相（纯草酸盐和剩余的残留物）。该过程通过酸化（HCl 6N）去除碳酸盐并将草酸盐溶解到上清液中，将矿物质和风吹有机化合物留在残渣中。通过 FTIR 分析和通过14C测年表明确实获得了纯草酸盐粉末。同一艺术面板上各种吸积物的 AMS 放射性碳结果提供了从现代时期到 2410 ± 35 BP 的年龄。根据这些初步结果，可以考虑更有针对性的抽样活动，以提供终点前对于岩石艺术。