Biological rock crusts (BRCs) are ubiquitous features of rock surfaces in drylands composed of slow-growing microbial assemblages. BRC presence is often correlated with rock weathering, soiling effect or mitigating geomorphic processes. However, their development rate is still unknown. In this work, we characterised and dated BRCs in an arid environment, under natural conditions, by integrating archaeological, microbiological and geological methods. To this end, we sampled rocks from a well-documented Byzantine archaeological site and the surrounding area located in the central Negev, Israel. The archaeological site, which is dated to the fourth to seventh centuries CE, was constructed from two lithologies, limestone and chalk. BRC started developing on the rocks after being carved, and its age should match that of the site. Using stable carbon and oxygen isotope ratios, we confirmed the biogenic nature of the crusts. The BRC samples showed mild differences in the microbial community assemblages between the site and its surroundings, irrespective of lithology, confirming the dominance of aeolian inoculation sources. All BRCs were dominated by Actinobacteria, Cyanobacteria and Proteobacteria. We further measured the BRC thickness on 1700-year-old building stone blocks and determined it to be 0.1–0.6 mm thick. Therefore, a BRC growth rate was estimated, for the first time, to be 0.06–0.35 mm kyr⁻¹. Our dating method was then validated on a similar archaeological site located ca. 20 km away, giving comparable values. We propose that BRC growth rates could be used as an affordable yet robust dating tool in archaeological sites in arid environments.

中文翻译：

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微生物和地质考古记录揭示了沙漠岩石表面群落的生长速度、起源和组成

生物岩壳 (BRC) 是旱地岩石表面普遍存在的特征，由生长缓慢的微生物组合组成。BRC 的存在通常与岩石风化、污染效应或减轻地貌过程有关。然而，它们的发展速度仍然未知。在这项工作中，我们通过整合考古、微生物和地质方法，对自然条件下干旱环境中的 BRC 进行了表征和测年。为此，我们从以色列内盖夫中部一个有据可查的拜占庭考古遗址和周边地区采集了岩石样本。该考古遗址的历史可追溯至公元四世纪至七世纪，由石灰岩和白垩这两种岩性构成。BRC在雕刻后开始在岩石上发育，其年龄应该与现场相匹配。使用稳定的碳和氧同位素比率，我们证实了地壳的生物成因。BRC 样本显示该地点与其周围环境之间的微生物群落组合存在轻微差异，而与岩性无关，证实了风积接种源的主导地位。所有 BRC 均以放线菌、蓝藻和变形菌为主。我们进一步测量了具有 1700 年历史的建筑石块的 BRC 厚度，并确定其厚度为 0.1-0.6 毫米。因此，首次估计 BRC 增长率为 0.06-0.35 mm kyr 所有 BRC 均以放线菌、蓝藻和变形菌为主。我们进一步测量了具有 1700 年历史的建筑石块的 BRC 厚度，并确定其厚度为 0.1-0.6 毫米。因此，首次估计 BRC 增长率为 0.06-0.35 mm kyr 所有 BRC 均以放线菌、蓝藻和变形菌为主。我们进一步测量了具有 1700 年历史的建筑石块的 BRC 厚度，并确定其厚度为 0.1-0.6 毫米。因此，首次估计 BRC 增长率为 0.06-0.35 mm kyr^-1。我们的测年方法随后在位于约 1 的类似考古遗址上得到验证。20 公里，给出可比较的值。我们建议 BRC 增长率可以用作干旱环境中考古遗址中负担得起但强大的测年工具。