Table 1 Formation conditions of climatically sensitive lithologies and the categories used in this study.
Lithology | Categorya | Weightb | Formation conditionsc | References |
|---|---|---|---|---|
Calcretes | C | 1.00 | Persistent semi-arid to arid continental conditions on millennial timescales, with fluctuating groundwater level. Evaporation > precipitation at least 6 months in every year; 140 mm < MAP < 1400 mm. | |
Evaporites (general) | E | 1.00 | Persistent arid to semi-arid conditions, where evaporation typically exceeds precipitation. Quaternary evaporite deposits are observed to form under fully arid and seasonally arid conditions, under polar to tropical temperatures. | |
Anhydrite | E | 1.00 | Arid to semi-arid conditions, often within a (partially) isolated basin. As for general evaporites. | |
Gypsum | E | 1.00 | Arid to semi-arid conditions, often within a (partially) isolated basin. As for general evaporites. Most though not all modern gypsum forms under conditions of MAP < 400 mm and evaporation > precipitation in every month of the year. | |
Halite | E | 1.00 | Arid to semi-arid conditions, often within a (partially) isolated basin. As for general evaporites. | |
Evaporite pseudomorphs | E | 0.75 | Arid to semi-arid conditions, often within a (partially) isolated basin. As for general evaporites. Down-weighted due to reliance on interpreting the original morphology of the pseudomorphs. | |
Length-slow chalcedony | E | 1.00 | Arid to semi-arid alkaline soils; forms in association with sulfate and halite products. | |
Striated dropstones | G | 1.00 | Cold (freezing) conditions nearby. Outsized clasts may be down-weighted if glacial origin is uncertain. | |
Tillite | G | 1.00 | Cold (freezing) conditions with significant land ice present. Diamictite texture may be down-weighted if glacial origin is uncertain. | |
Bauxite | L | 1.00 | Intense continental weathering under high humidity and temperature; evaporation < precipitation in 9 to 11 months of the year; MAAT > 25 °C and MAP > 1800 mm, or MAAT > 22 °C and MAP > 1200 mm. | |
Kaolinite | L | 1.00 | Intense continental weathering under high humidity and typically high temperature, though temperate-region kaolinite deposits are known; low pH is also required and is commonly derived from the presence of humic acids. | |
Laterite | L | 1.00 | Intense continental weathering under high humidity and temperature; evaporation < precipitation in 9–11 months of the year; MAAT > 25 °C. | |
Oolitic ironstones (berthierine, chamosite) | L | 1.00 | Proximal to intense continental weathering under high humidity and temperature; energetic shallow marine setting. Oolitic ironstones may be down-weighted if the primary mineralogy is uncertain. | |
Oolitic limestone | O | 1.00 | Warm, (sub)tropical energetic shallow marine setting; starved of clastic sediment input; (super)saturated with respect to calcium carbonate, which supersaturation may be aided by an arid climate. |
