Embedded Files
Paleosols
Paleosols
“Detailed field description of paleosols and pedogenic carbonates at different stratigraphic horizons from three localities reveal four main pedotypes (vertisols, gleysols, oxisols, and protosols). Major elements geochemistry suggests variable redox conditions, and a sub-humid to humid paleoclimate with seasonal precipitations during the paleosol development. Vertisols and gleysols reflect reducing conditions, while protosols and oxisols reflect oxidizing conditions."
Fossil soils have also shown four types, Entisol-like, Inceptisol-like, Aridisol-like and argillic Inceptisol-like. Pretty well all sorts of soils were present then. The depths of carbonate nodules indicate a generally semiarid–subhumid climate alternating with arid–humid and cool/warm–temperate climates, which terminated in a dry, subhumid, humid/perhumid and superhumid moisture regime characterized by steppe/wet or rain forest floral provinces. These climatic fluctuations may have been related to the fragmentation of Pangea and regional tectonic uplift during the Middle Jurassic. There was low pCO2 levels within the range of ∼100 ppm–∼890 ppm
The morphological features of type I paleosols suggest very poor soil formation and that bioturbation is the main pedogenic processes. Yet the Inceptisol-like paleosols, constituting nearly 20% of soils had a thickness of 15–30 cm in sequences of A–R or A–AC horizons and up to 90cm deep. “The structures are constituted of fine–or medium-sized, moderately developed angular blocky peds, and structureless or massive horizons, while the paleosol textures are formed of muddy sandstone or siltstone and silty mudstone." (Li et al 2022)
The yellow arrows point to branching carbonized root structures surrounded by grey ‘rhizohaloes’ - elongate coloured mottles. If only we could look at the roots more closely to see if there were any springtails - despite the unlikelihood of them being preserved.
All the signs of soil as we know today were there then.
A study of Jurassic palaeosols in Denmark found "the development of waterlogged Gleysols in backswamp areas, and less acid Histosols in closed bays of coastal swamps. In the latter case peat-bogs were formed. In topographically higher areas, as levee banks and crevasse splays, freely drained Podzols developed." (Arnorff 1993 )
Ichnofabrics
Ichnofabrics
Ichnofabric refers to the sedimentary structures resulting from the activities of organisms, including burrowing and bioeroding, which provide valuable information about ecological conditions, environmental settings, and substrate properties in sedimentary units. They may give us a sense of how floodplains could become soil. "Complex continental ichnofabrics were recorded in late Jurassic–late Miocene deposits" (Bedatou et al 2009)
"The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events provided the resource inputs necessary for their living during rainy seasons. The results also show that in fluvial systems with high discharge variations, the boundaries between a “pre-desiccation suite” and a “desiccation suite” in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels." (Nascimento et al 2023)
Some podzols feature a well-developed E horizon, where leaching removed minerals and organic acids, leaving behind a bleached, sandy layer above the B horizon.
Well-developed Horizons
Well-developed Horizons
The increase in plant diversity and more complex root systems led to better-developed O, A, and B horizons. The roots of flowering plants penetrated deeper into the soil and facilitated the development of thicker and more distinct horizons. I also believe that the increased number of oribatid mites, especially in deeper levels, would increase the mixing, but can find no research into this.
The formation of podzolic soils became more common, particularly in temperate climates. Podzolic soils are forested soils that form in acidic parent materials.
Types
Types
- O Horizon (Organic Layer): This is the topmost layer, rich in organic material such as decomposed leaves, plants, and animal residues.
- A Horizon (Topsoil): Often called the "topsoil," this layer is a mix of organic material with mineral particles and is the most fertile part of the soil.
- B Horizon (Subsoil): This layer accumulates minerals like iron, clay, aluminium, and organic compounds that are leached from the upper horizons, often called the "zone of accumulation."
- C Horizon (Parent Material): Composed mainly of large rocks and partially disintegrated parent material, little affected by soil-forming processes and lies above the bedrock.
Podzols
Podzols
Podzols are usually distributed "under coniferous forest and on non-calcareous nutrient poor parent material and are characterized by a spodic (gray, leaching of iron (Fe), aluminum (Al) and organic matter) horizon. The role of litter derived from the understory vegetation has recently been shown to be involved in these processes for boreal forest stands. Thus, the typical podzolization processes in boreal forests with leaching of dissolved organic matter and elements are possibly mainly driven by decomposition of the litter provided by the understory vegetation like Vaccinium myrtillus. "
Humic Podzols have a Bh horizon enriched in organic matter (humus) that has been translocated from the overlying organic horizon (Of) and the bleached Ae horizon. This indicates increased presence and movement of humus, perhaps due to the denizens of dirt.
Humic Podzol
It is clear that soil developed dramatically in this period in terms of differentiated horizons and different types.
Page updated
Google Sites
Report abuse