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Triassic Palaeosols
Triassic Palaeosols
The observed vertical progression in the major paleosol types from Vertsols to Gleysols and Oxisols implies a systematic change in the number of wet months, most probably in response to regional tectonics and long-term climate change. Paleosols of Triassic terrain can be found across the world from Europe, the Rift Valley in Africa to the Antarctica.
There were temperate conditions “indicated by roots, logs, and leaves of woody plants and the degree of chemical weathering and clay formation within the paleosols…Silt infiltration structures around root traces and in cracks within the paleosols are evidence for a seasonally snowy climate…Other evidence of climatic seasonality includes well-defined growth rings in fossil wood, and abscission scars at the base of fossil leaves. Diverse broadleaf plants, and noncalcareous paleosols, indicate a humid climate with mean annual precipitation of about 1200 mm.” (Retallack and Alonso-Zarza 1998,
Root traces
Root traces
"The lack of organic matter and deep penetration of the white root traces are evidence of well drained soils. In well aerated soils, root penetration and decomposition of organic matter are unhindered. The first phase in the formation of the white root traces would have been rotting out of the buried root traces, followed by filling with clay and silica. Some of the concentric fills could have been initiated before burial of the soil., when soil clasts and silt-size mineral grains fell down into a widening crack between rotting root and its matrix. Most of the fill was probably formed during burial of the paleosol, because so many of them are free of sediment that fell into associated insect burrows...The white root traces are likely permineralised logs in resistance to burial compaction". Retallack and Alonso-Zarza 1998,
Hmm, so there were visible insect burrows, which fits with the appearance of soil-dwelling insect larvae in this period
White root traces
Hammer 25cmThe palaeosols often exhibit features associated with extreme arid conditions, aridification, global warming, and ecological collapse due to the EPE's aftermath. One of the significant features in some Triassic palaeosols is the formation of calcrete crusts, which indicate intense periods of evaporation and reduced vegetation. These crusts form under conditions where the soil is subjected to high temperatures, little precipitation, and reduced biological activity—conditions that were prevalent after the massive biodiversity loss during the EPE.
Arid and Semi-Arid Paleosols: The Early Triassic was characterized by widespread aridification, and paleosols from this time often have characteristics such as:
Calcrete horizons (carbonate crusts) that form under semi-arid to arid conditions.
Gypsum and evaporite minerals in certain regions, which also indicate extreme evaporation and dry climates.
Reduced organic matter, reflecting the collapse of terrestrial ecosystems and plant life after the extinction even
Impacts of Global Warming: The extreme warming following the EPE, driven by volcanic activity from the Siberian Traps and the release of greenhouse gases, further contributed to the formation of these paleosols. The early Triassic was one of the hottest periods in Earth's history, and the soils that developed were often poorly developed due to the harsh conditions.
Vertisols and Ferricrete Crusts: In some regions, paleosols show signs of shrink-swell clays, typical of Vertisols, which form in highly seasonal environments. These soils might display features like iron-rich crusts (ferricretes), which are linked to seasonal wet and dry cycles under a hot climate.
Biological Soil Crusts (BSCs): Although not a paleosol in the traditional sense, biological soil crusts could have also played a role in some arid and semi-arid environments. These crusts form from microbial and cyanobacterial activity in extreme conditions where vegetation is sparse, a situation likely prevalent in the Early Triassic after the extinction.
Key Example: Karoo Basin, South Africa
Key Example: Karoo Basin, South Africa
The Karoo Basin in South Africa contains well-studied Triassic paleosols, showing evidence of an arid to semi-arid climate with calcrete layers and gypsum deposits. These features indicate extreme drying and evaporative conditions that prevailed after the End-Permian extinction.
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