Abstract

Abstract. 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.

Highlights

  • In arid and hyper-arid environments where abiotic processes are considered the primary contributor to landform formation, barren rock surfaces, free of vegetation, are a ubiquitous feature (Owen et al, 2011)

  • In arid Biological rock crusts (BRCs), fungi are scarce (Lang-Yona et al, 2018), but our results suggest that Cyanobacteria and other taxa like Alphaproteobacteria and Actinobacteria play a key role in BRC development (Fig. 4c)

  • We suggest that local-scale environmental parameters play a major role in shaping the microbial taxa that colonise fresh rock surfaces in arid regions. This suggests that the BRCs cannot be regarded as passive deposits of microbial cells but should rather be seen as a filter selecting for a specific subset of adapted microbes that can persist and form a biofilm under these harsh conditions

Read more

Summary

Introduction

In arid and hyper-arid environments where abiotic processes are considered the primary contributor to landform formation, barren rock surfaces, free of vegetation, are a ubiquitous feature (Owen et al, 2011) These surfaces are exposed to multiple stress factors, such as lack of water, high radiation and extreme temperature fluctuations and represent the edge of biotic existence on Earth (Viles, 2008). BRC structure, when developed on carbonate-rich minerals (e.g. limestone), often consists of a hardpan-laminated structure composed of masses of micritic to microsparitic carbonate layers interbedded with microbial coatings. Such laminated structures were previously reported by Alonso-Zarza and Wright (2010) as terrestrial calcretes. BRC inoculum has been proposed to originate from settled dust

Objectives
Methods
Results
Discussion
Conclusion
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call