Figure 1.
A map showing the locations of sampling sites, where Nubian sandstone S1-S6 (A) and Theban limestone (B) have been collected.
Table 1.
Chemical composition of the studied samples.
| [Wt. %] | Sandstone S3 | Sandstone S6 | Limestone TL |
|---|---|---|---|
| SiO2 | 92.57 | 85.67 | 7.08 |
| Al2O3 | 3.12 | 0.96 | 0.54 |
| Fe2O3 | 1.18 | 7.94 | 0.33 |
| MgO | 0.07 | 0.11 | 0.51 |
| CaO | 0.07 | 1.56 | 50.22 |
| Na2O | 0.07 | 0.13 | 0.15 |
| K2O | 0.87 | 0.19 | 0.08 |
| TiO2 | 0.84 | 0.18 | 0.03 |
| LOI | 1.0 | 3.1 | 40.7 |
Figure 2.
Flowchart presenting experimental approach undertaken to decipher stone weathering.
Figure 3.
Microphotographs of Nubian sandstone (S3, S6) taken in plane-polarized (left column) and cross-polarized light (right column).
Figure 4.
Results of X-ray diffraction and thermal analysis of Theban limestone (TL) and Nubian sandstone (S3, S6). Mineral abbreviations: cal-calcite, qz-quartz, kln-kaolinite, hl-halite, afs-alkali feldspar, zrn-zircon, gth-goethite, hem-hematite, mag-magnetite, gp-gypsum, lpc-lepidocrocite (Warr, 2021); dh-dehydration, dxo-dehydroxylation.
Figure 5.
BSE images and EDS spectra of Nubian sandstone (S3, S6) and Theban limestone (TL) before leaching experiment. 1 – euhedral dolomite; 2 – bioclast; 3 – Fe-bearing phases encrusting bioclast; 4, 9 – alkali feldspar; 5 – quartz; 6, 10 – Fe-bearing phases in matrix; 7, 11 – kaolinite; 8 – magnetite.
Figure 6.
BSE images and EDS spectra of Nubian sandstone (S3, S6) and Theban limestone (TL) after leaching experiment. 1 – bioclast; 2 – bioclast covered with biofilm, 3 – euhedral dolomite; 4 – quartz and biofilm; 5 – syntaxial quartz overgrowths; 6 – bacteria on kaolinite aggregate; 7 – kaolinite aggregate; 8 – magnetite; 9, 11 – Fe-bearing phases; 10 – single kaolinite flake.
Figure 7.
Microphotographs of Theban limestone (TL) taken in plane-polarized (left column) and cross-polarized light (right column).
Figure 8.
Evolution of elements leaching from studied sandstones throughout the experiment (BAC: growth medium with bacteria filtered at <0.22 μm; MED: sterile growth medium; H2O: sterile water). Error bars present standard deviation of the replicate values.
Table 2.
Specific conditions set in the incubation experiments.
| Incubation | Name | Characteristics of the constituents | Presence of bacteria | Initial pH | Final pH S3 | Final pH S6 | Final pH TL | Siderophore concentration | Proxy |
|---|---|---|---|---|---|---|---|---|---|
| Ultrapure water | WAT | none | - | 5.6 | 8.7 | 8.6 | 8.1 | - | Neutral unaggressive conditions |
| Growth medium | MED | Inorganic, organic (succinic acid) | - | 7.0 | 7.8 | 7.8 | 8.0 | - | Chemical weathering |
| Growth medium with bacteria Pseudomonas fluorescens | BAC | Inorganic, organic (succinic acid, microbially-derived compounds including siderophore) | + | 7.0 | 8.7 | 9.1 | 9.2 | S3: 45.2 μM L−1 S6: 75.5 μM L−1 TL: 90.6 μM L−1 | Biotic weathering |
Figure 9.
Evolution of elements leaching from studied limestone throughout the experiment (BAC: growth medium with bacteria filtered at <0.22 μm; MED: sterile growth medium; H2O: sterile water). Error bars present standard deviation of the replicate values.