Table 1.
A selection of sites preserving fossiliferous concretions.
| Locality | Formation | Age | Preservation | Fossils present | References |
|---|---|---|---|---|---|
| Norfolk, United Kingdom | - | Holocene | Siderite, calcite and iron monosulfide concretions | Plants, Invertebrates | Pye (1984), Pye et al. (1990), Allison and Pye (1994) |
| Kangerlussuaq, Greenland | - | Holocene | Carbonate concretions in clay | Fish (capelin: Mallotus villosus) | Mojarro et al. (2022) |
| Ottawa, Canada | - | Holocene | Carbonate concretions in clay | Fish (capelin: Mallotus villosus) | Mojarro et al. (2022) |
| Kent, United Kingdom | London Clay Formation | lower Eocene | Pyrite, apatite, phosphate, and calcite concretions in clay | Plants, Invertebrates, Fishes, Reptiles, Birds, Mammals | Allison (1988b), Huggett (1994), Huggett et al. (2000) |
| Magdalena Valley, Colombia | Cretaceous black shales | Lower Cretaceous | Carbonate concretions in shales | Invertebrates, Fishes | Weeks (1953, 1957) |
| Santana Group, Chapada do Araripe, Brazil | Romualdo Formation, Santana Group | Lower Cretaceous | Carbonate concretions in mudstones/shales with minor limestone | Plants, Invertebrates, Fishes, Amphibians, Reptiles, Birds | Mabesoone and Tinoco (1973), Martill (1988, 1989, 1990, 1993, 2007), Maisey (1991), Fara et al. (2005), Varejão et al. (2021) |
| Cerritos Bayos, Chile | Cordillera de Domeyko | Upper Jurassic | Calcareous concretions in black, sandy, gypsum-rich shales | Invertebrates, Fishes, Reptiles | Schultze (1989), Arratia and Schultze (1999) |
| Posidonia Shale, Germany | Sachrang Formation | Lower Jurassic | Pyritiferous calcite concretions in shale | Plants, Invertebrates, Fishes, Reptiles | Plet et al. (2016, 2017) |
| Mazon Creek, Ilinois, USA | Francis Creek Shale Member, Carbondale Formation | Upper Carboniferous | Siderite (iron carbonate) concretions in shale | Plants, Invertebrates, Fishes, Amphibians, Reptiles | Johnson and Richardson (1966), Woodland and Stenstrom (1979), Baird et al. (1985a, 1985b, 1986), Archer et al. (1995), Clements et al. (2018) |
| Gogo Station, Western Australia, Australia | Gogo Formation | Middle–Upper Devonian | Calcareous concretions hosted in shales and siltstones with lenses of limestone | Radiolarians, Invertebrates, Fishes | Melendez et al. (2013b), Lengger et al. (2017), Trinajstic et al. (2022a,b) |
| Herefordshire, United Kingdom | Coalbrookdale Formation | middle Silurian | Carbonate concretions hosted in bentonite | Invertebrates | Siveter et al. (2020) |
| Fezouata Biota, Morocco | Fezouata Formation | Lower Ordovician | Siliceous concretions in shale | Invertebrates (anomalocaridids) | Gaines et al. (2012), Van Roy et al. (2015), Saleh et al. (2021) |
| Västergötland, Sweden | Alum Shale Formation | upper Cambrian | Carbonate concretions in black shale (‘Orsten’-style concretions) | Invertebrates | Dworatzek (1987), Maeda et al. (2011) |
| North China | Xiamaling Formation | middle Mesoproterozoic (~1.39 Ga) | Silicified bitumen concretions in black shale, green chert | Bacteria; biofilms | Wang et al. (2017), Liu et al. (2019), Liu A. et al. (2020) |
Note the broad geographic and temporal ranges of these deposits. Whether or not the concretions at these sites (or others not included in this table) were formed as a consequence of microbial activity remains to be demonstrated.