Palaeosols

145 - 66 mya Cretaceous

Dinosaurs Abominable Mystery Leaves Roots Mycorrhiza

Entisol

Inceptisol

Paleosols

Early Cretaceous paleosols have been found in a Chinese river bed which show us the preserved pedogenetic features, like soil horizons, soil structure, and root traces. They were classified in today’s types as Entisols ( little or no evidence of soil formation ), Inceptisols (Young soils with subsurface horizon formation , Aridisols(dry soils under desert) and Alfisols (forested soils with a light-coloured layer over clay) - a wide range of types.

Aridisol

Alfisol

Histosol

"The paleosol record of the Early Cretaceous reveals a suite of non-calcareous Histosols and Ultisols, as well as stump casts, indicative of humid temperate ecosystems. At some stratigraphic levels, frigid temperatures are indicated by clastic dykes (ice wedges), load casts of mud (periglacial convolutions), and coal-mantled stone rolls (aapamires). The largest tree stumps and thickest paleosols correspond to known Early Cretaceous greenhouse spikes, as revealed by stomatal index." Retallack 2023

The increase in plant diversity and more complex root systems led to better-developed O, A, and B horizons. The roots of flowering plants, which penetrated deeper into the soil, facilitated the development of thicker and more distinct horizons.

Ultisol

Crusty

One sort of paleosol, that had been round before, came into prominence in this period. It is a biological ‘soil crust’ (BSC), which can tell us about the sedimentary processes as well as the prevailing paleoclimate. Modern biological soil crusts develop under semiarid to arid conditions and are characterized by diverse communities of micro- and macro-organisms. It is an unmistakably like a modern -day biological crust, with the same pinnacles crinkle on its surface.

Creatures & crusts

“Aphelacaridae (Sarcoptiform mites) Cosmochthoniidae (Oribatid mites), Micropsammidae & Nanorchestidae (Endeostigmatid mites), Stigmaeidae (Trombidiform mites), and Tydeidae (Acariform mites) were families common to both locations, both crust stages and both depths. Most families present were microphytophagous (consuming microorganisms like fungi, bacteria, and algae),either strictly or as facultative predators ( have a well-defined diet, but may also consume a broader range of prey.). These findings are compatible with the microfloral (bacterial) nature of biological soil crusts dominated by lichen, moss, and cyanobacteria. Occasional predation of nematodes and protozoa grazing on the crust flora is likely. Other groups identified included zoophages (consumes animal matter), necrophages (consuming decomposing dead animal biomass) and macrophytophages (Eating higher plant material only)… a ‘core community (Neher et al 2009)

Fossilized Cretaceous crusts, including those formed by ancient biological activity (BSCs) are distinguished from caliche, ferricrete, and duricrust based on their composition, structure, formation processes, and environmental context.

Composition: The mineral content is the most significant distinguishing feature. Caliche is dominated by calcium carbonate, ferricrete by iron oxides, duricrust can include various minerals like silica, and fossilized biological soil crusts (BSCs) show signs of organic or microbial structures.
Formation Process: Caliche forms by carbonate precipitation from groundwater, ferricrete through oxidation and precipitation of iron, and duricrust from mineral cementation. Fossil BSCs are formed by microbial activity and later buried and preserved through lithification processes.
Physical Characteristics: Caliche and ferricrete form hardpan layers, while fossilized BSCs typically show micro-layering or biological textures. Duricrusts can be more variable in appearance but are always highly cemented.
Context of Formation: Fossil BSCs are associated with land surfaces that experienced low vegetation cover, while caliche, ferricrete, and duricrust reflect mineral precipitation and accumulation under specific climatic conditions.

In the Field:

In the Cretaceous palaeosols of the Western Interior Seaway, caliche might be distinguished by the presence of carbonate nodules and root casts in a semi-arid environment. In contrast, a ferricrete layer could be identified by its reddish coloration, iron oxide content, and formation in a more tropical or subtropical, deeply weathered soil.
Fossilised BSCs show microbial structures and lack the extensive mineral cementation seen in the other types of crusts. By considering composition, formation processes, and context, these different types of crusts can be effectively distinguished from one another in paleosols.

Biological Soil Crusts

Description: Biological soil crusts (BSCs) are formed by the activity of microorganisms like cyanobacteria, fungi, lichens, and mosses. Fossilized examples are rare but provide evidence of microbial life on land.
Identification:
- Microscopic Structure: Fossil BSCs retain signs of microbial filaments, cellular structures, or microbially induced sedimentary structures (MISS).
- Thin Laminations: These crusts often have very fine, thin laminations that represent successive layers of microbial growth.
- Chemical Signatures: Fossilized BSCs might show organic geochemical markers, like specific hydrocarbons, or isotopic ratios (e.g., δ13C) linked to microbial activity.
- Absence of Extensive Cementation: Unlike caliche or duricrust, BSCs don’t show significant mineral cementation, though they may be preserved in carbonate or silicate matrices.
Environmental Context: BSCs often form in environments with limited vegetation, like semi-arid and arid regions, and are linked to early terrestrial ecosystems.

Caliche (Calcrete)

Description: Caliche (or calcrete) is a soil layer rich in calcium carbonate, formed by the precipitation of carbonate minerals from groundwater or atmospheric CO₂ in arid to semi-arid climates.
Identification:
- Carbonate Composition: Caliche consists mostly of calcium carbonate (CaCO₃), often forming nodules, hard pans, or crusts in soil profiles.
- Pedogenic Features: Caliche often shows root casts, carbonate nodules, or rhizoliths, where plant roots were present and led to the localized precipitation of carbonates.
- Hardpan Layers: In more developed caliche profiles, there may be solid, cemented layers of carbonate, indicating prolonged evaporation and re-precipitation.
- Isotopic Analysis: Carbon and oxygen isotope analyses (δ13C and δ18O) can help distinguish caliche, with isotopic signatures reflecting the interaction between atmospheric CO₂ and carbonate formation.
Environmental Context: Caliche forms in arid to semi-arid environments with intermittent wetting and drying cycles, where groundwater rises and evaporates, leaving carbonate deposits.

Ferricrete

Description: Ferricrete is a type of duricrust rich in iron oxides (e.g., hematite and goethite), formed in tropical to subtropical climates with intense weathering and oxidation of iron-bearing minerals.
Identification:
- Iron Oxide Composition: Ferricrete is composed predominantly of iron oxides, giving it a reddish to brown color. The presence of hematite and goethite is a key indicator.
- Hardened Iron-Rich Crust: Ferricrete forms hardpan layers or nodules, cemented by iron oxides, often in the B horizon of a soil profile.
- Massive or Pisolitic Structures: Ferricretes can display pisolitic (rounded, pea-sized structures) or massive iron oxide accumulations.
- Weathering Indicators: Often associated with deeply weathered profiles in areas with high rainfall and lateritic conditions.
Environmental Context: Ferricretes are linked to tropical, highly weathered environments where intense leaching removes silicates and leaves behind iron-rich crusts.

Duricrust

Description: Duricrust is a general term for hardened crusts that form at or near the surface of soils due to the accumulation and cementation of minerals, including silica, iron, or calcium carbonate.
Identification:
- Mineralogical Composition: Duricrust can vary widely in composition, including silcrete (silica-dominated), calcrete (carbonate-dominated), ferricrete (iron-dominated), or gypcrete (gypsum-dominated).
- Hard, Cemented Layers: Duricrust typically forms a very hard, resistant layer at the surface or just below the surface, preventing further soil development below.
- Silica or Other Mineral Cementation: Duricrusts like silcrete are cemented by silica (SiO₂), often creating highly durable, quartz-rich layers.
- Lack of Biological or Organic Indicators: Unlike fossilized BSCs, duricrusts lack direct evidence of biological activity or organic material, though they can form in soils influenced by biological processes.
Environmental Context: Duricrusts form in arid to semi-arid climates, where intense evaporation leads to the accumulation of minerals that cement the soil.

Biological Soil Crusts (BSCs)

The binding action of cyanobacteria, green algae, lichens, microfungi, and mosses, would increase aggregation of BSCs which deters wind and water erosion and increases ‘infiltration' - the process by which water on the ground surface enters the soil to hold water for later. It would seem these soil crusts would have conquered the dry conditions so that other larger, and perhaps different, specially adapted plants could grow in it and arthropods live in it. It has obvious lessons for us today.

"Arctic, Antarctic and alpine areas dominated by a range of extreme environmental conditions which impose severe pressure on biological life, particularly for vegetation: they begin where trees no longer dominate the vegetation, usually have temperatures below 10 ∘C in the warmest month and are characterized by snowfall, at least in winter. Biological soil crusts (BSCs) are formed by adhesion of soil particles to exopolysaccharides (EPSs) excreted by cyanobacterial and green algal communities, the pioneers and main primary producers in these habitats." (Jung et al 2018)

There do not seem to be any animals involved with this crust

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