Tag Archives: soil parent material

Atlas of soils and weathering

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typical soil profile

Soil, dirt, mud

The stuff kids get covered in when they’re having fun.

A veneer on Earth’s crust that provides sustenance in one form or another for all land-air living creatures, including us.  Without soils there would be no food web. No us!

Homo sapiens has learned to use soil to her advantage; growing things to eat, to construct shelter, to decorate. We have learned to utilize soils to the hilt. In fact on a global basis we have  taken so little care of them that they have become an endangered species. In our haste to produce food, to irrigate, to scythe through forests, to clear land for some other use, we have damaged soils, in many cases beyond repair.  Humanity, in its ignorance, greed and hubris, has managed to seriously compromise the utility of soils – the very things that make life viable.

From a structural perspective soils are quite simple; there is topsoil that contains a mix of organic matter derived from plants, macro- and micro-organisms, plus minerals derived primarily from the underlying sediment or rock (parent material).  This structure is illustrated in the profile image above.

From a biological perspective, soils are complex. Apart from the obvious worms and small critters, there is a burgeoning microflora – fungi and bacteria; and it is the microflora that does most of the work to create a vital growing medium. The microflora breaks down fresh organic matter converting it to humus, and converts nutrients like nitrogen, potassium, phosphorous and many trace elements, into water-soluble forms that plants can metabolize. A vital topsoil requires a healthy microbiota. Soils that are regularly exposed to herbicides, bactericides and fungicides will, over time, become depauperate in useful microflora.

soil fungal threads

Classification of soils can be complicated. In this Atlas I use a simple textural classification, summarized in the diagram below. It is a US Dept. of Agriculture classification; most other countries use this or slightly modified versions.

This link will take you to an explanation of the Atlas series, the ownership, use and acknowledgment of images.  There, you will also find links to the other Atlas categories.

Click on the image for an expanded view, then the ‘back page’ arrow to return to the Atlas.

The images

soil profile soil on volcanic ash

Left: Silt-sand loams developed on Late Pleistocene fluvial pebbly volcaniclastics (Hinuera Formation, Waikato, NZ). The transition from modified sediment to parent material is irregular. Right: Topsoil developed on multiple ash layers; remnants of an older (fossil) soil is located above the pale band of ash (Waikato, NZ).

 

soil on ignimbrite soil on co-ignimbrite ash

Thin (pumice) loam on  airfall ash, that overlies partly welded ignimbrite (the orange ash layers may be co-ignimbrite). Iron oxide staining indicates groundwater seepage and mineral alteration. Mamaku, north of Rotorua N.Z.

 

soil on paleotopography

Three sets of small V-shaped paleovalleys and intervening ridges cut into welded Mamaku Ignimbrite (about 220,000 years old), draped by at least three ash fall deposits and thin paleosols (paleosoils). The entire outcrop is overlain by a more recent soil and modern vegetation. North of Rotorua, NZ

 

soil on coastal plain gravels

Thin sandy loam topsoil and iron-stained layer on coastal plain gravels. The upper part of the topsoil has been disturbed by cultivation. The normal position of the watertable is at the transition to gray gravel. Kaiua, Thames coast east of Auckland, NZ.

 

soil on sand dunes soil on sand dunes

Eroded sections of coastal dunes, Raglan, N.Z.. Spinifex roots penetrate up to 2m into the sand. Soils here are very low in organic matter, almost 100% sand with high permeability and little capacity for water retention.

 

Spinifex roots in sand sand dune vegetation

Coastal dune root systems (Spinifex and Lupin). Much of the organic matter is oxidized rapidly. Dune instability means that topsoil formation is meagre.

 

Pleistocene paleosols Pleistocene soil profile

Pleistocene dune sands are overlain by peat and leaf litter from an ancient coastal, Podocarp forest. Left: Old dunes cut by an uplifted marine terrace, capped by peat.  Right: Cross-bedded dune sands overlain by thin woody peat (O layer). The B layer here is sand enriched in iron oxides precipitated by ancient fluctuating water tables. Great Exhibition Bay, northern NZ

 

Pleistocene peat Pleistocene peat profile Pleistocene peat profile

Pleistocene woody peat and leaf litter at top (O layer), underlain by thick, blocky weathered, silt loams with abundant roots and buried logs. Great Exhibition Bay, northern NZ

 

reduction spots in sand dune reduction spots in dune sand

Semiconsolidated, cross-bedded Pleistocene dune sands beneath a peat. Here, the parent sands have reduction spots derived from leaching of iron oxides. Great Exhibition Bay, northern NZ

Liesegang rings

Liesegang rings are a common manifestation of shallow weathering in permeable sandstone.  The ring-like patterns form as iron oxides precipitate in concert with migrating groundwater. Mokau Sandstone, north Taranaki, NZ

 

soil iron pan in sand dunesinterdune lake deposits

Left: Remnants of a soil formed over stabilized Pleistocene dune sands. The abrupt steep-dipping contact with a younger set of dune deposits is delineated by resistant limonite pans. Right: The muddy loam indicated as ‘P’ represents a small Pleistocene interdune pond or lake; here overlain by multiple dune crossbeds. Kariotahi, west Auckland, NZ

 

spheroidal weathering in basalt spheroidal weathering in sandstone spheroidal weathering iron pan

Chemical weathering of bedrock. Left: Spheroidal weathering in an andesite lava flow promoted by mineral dissolution in shallow percolating groundwater. Late Pliocene Karioi volcano. Center and Right: A mix of spheroidal weathering and iron oxide precipitation in indurated Triassic sandstone-shale, where alteration patterns are strongly influenced by bedding and fractures; Kiritehere, NZ

 

muddy loam profile silt clay loam profile

Left: Profile of muddy loam developed on weathered turbidite sandstone-mudstone. Near Wellsford, north Auckland NZ. Right: Silty clay loam developed on Carboniferous shale, Cliffs of Moher, west Ireland

 

Alpine clay gravel loam Alpine clay gravel loam profile Alpine clay gravel loam profile

Gravelly clay loams and clays developed on steep alpine mountain slopes, Mt. Garibaldi, British Columbia. The organic layer is either very thin or absent. On the left, the parent material is probably lacustrine clay.

 

stoney silt clay loam Tuscany stoney silt clay loam Tuscany stoney silt clay loam Montefioralle

Typical stoney silt-clay loams of Tuscany; the location of Chianti Classico and olives. Bedrock parent material consists of Cretaceous-Paleogene marls, sandstones and shales. Left and Center: The 12th century fortification is Monteriggioni. Right: The hilltop village of Montefioralle.

 

permafrost soil patterned ground in permafrost

Arctic soils riven with permafrost. Left: Frozen muddy loam undergoing summer melt. Right: typical patterned ground in Arctic tundra.

 

weathered Atacama alluvial fan Atacama desert varnish

Arid soil in the Chilean Atacama commonly lack any organic component. Left: exposed surface of an inactive alluvial fan contains a mix of stoney material, sand, silt and mud. Calcite cements are common in some deposits. Right: Desert varnish, a common feature of prolonged, arid climate weathering. The varnish consists of silica, iron and manganese slowly leached from the original rock, and re-precipitated as oxides.

 

weathered lapilli soil

Weathering of basaltic lapilli below a very thin, incipient topsoil, shows gradual redistribution of iron oxides. The volcanic deposits are very young – about 800 years. Rangitoto, Auckland, NZ

 

soil creep Kansas soil creep and clay gravel loam soil creep and clay gravel loam

Left: Soil creep in sub-vertical shale, east Kansas, beneath a stoney clay loam. Center and Right: Old Red Sandstone bedrock extends into the low cliff where it is broken and gradually incorporated into gravelly colluvium by soil creep. The overlying thin sandy loam is formed predominantly on wind-blown sand. Red Strand, south Ireland.

soil creep County Cork

Soil creep in vertically dipping Devonian shale acts to incorporate shale slivers into the overlying clay-silt loam. Kinsale, south Ireland.

 

Burrens clints and grykes Miocene karst Takaka

Karst, common weathered landforms in carbonate rocks. Left: Clints and grykes formed by dissolution of carbonate along fractures in Carboniferous limestone, Burrens, Ireland. Right: Pinnacle dissolution structures in jointed Oligocene – Early Miocene limestone, Takaka, NZ (Image by Kyle Bland, GNS).

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Dirt; Soil degradation is a global problem we inflict on ourselves

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The media loves hyperbole. In some ways they remind me of ‘The end is nigh’ cartoon guy. This week (Oct 16, 2017) it’s ‘Ecological Armageddon’, a kind of end-of-the-world announcement that is founded on what looks like a drastic reduction in the insect biomass in parts of Germany; 75% of insects have disappeared since 1989. I don’t mean to trivialise these alarming reports, because if it turns out to be a phenomenon of more global extent (the collapse of bee colonies does not augur well), then the ramifications for activities like food production could be dire. The report’s authors note that the cause of this reduction is not yet understood, a sensible comment based on the limited scope of their study (the paper is Open Access). But their caution has not stifled speculation and hyperbole.

The demise of insects segues into the topic of this blog; the alarming rate at which soils, globally, are being degraded. There is a symbiotic relationship between soils and insects, linked primarily to the vital role both play in vegetation productivity. Continue reading

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