Soils of Cold to Temperate Climates PDF

 Soils of cold to temperate climates Podsol (a.k.a. Spodosol). Podsolisation: removal of Fe and/or Al from the A horizon and their accumulation in the B horizon. Strong acidic conditions needed to allow the mobility of Fe and Al in Podsols. Common in humid-te...

 Soils of cold to temperate climates Podsol (a.k.a. Spodosol). Podsolisation: removal of Fe and/or Al from the A horizon and their accumulation in the B horizon. Strong acidic conditions needed to allow the mobility of Fe and Al in Podsols. Common in humid-temperate climates. Podsol  Palaeosols Palaeosols are buried, fossilized soils. Palaeosols can be used to interpret ancient climates.  Paleosol located between the 1400 Ma Butler Hill Granite and the Cambrian Lamotte Sandstone. Photo taken by author in Missouri along State Highway 67. The weathered granite is overlain by a shaly regolith and the Lamotte sandstone overlaps this irregular surface  SEDIMENTS AND SEDIMENTARY ROCKS  Definitions Sediment – loose and unconsolidated material that forms at or near the Earth’s surface. Sedimentology – the study of sediments and the processes that form them. Lithification – the processes by which a sediment is converted into a sedimentary rock. Sedimentary petrology – the branch of geology concerned with the study of sedimentary rocks.  Sedimentary basins Sediments are deposited in sedimentary basins subsiding areas of the Earth’s crust which permit the net accumulation of sediment. – rift basins (e.g. East African Rift) – continental basins (e.g. Congo Basin) – continental margins Rift basins form by extensional tectonics and movement along normal fault planes passive continental margin  Sediment texture The texture of a sediment is the nature and arrangement of its’ grains. – grain size – sorting – roundness – grain fabric  Grain size The most important texture of a sediment. Grain size is a function of current strength: – the stronger the current the larger the particles deposited.  Sorting Refers to spread of the grain size distribution. Poorly sorted sediments consist of grains with a large variation in size. Well sorted sediments have grains that tend to be the same size. Sorting is related to the depositional mechanism: – sediments deposited from glaciers are poorly sorted – sediments from streams are better sorted – sediments from aeolian processes are even better sorted.  Roundness is a function of the number of corners a grain possesses. varies from angular to well rounded. increases with transport distance due to abrasion of particles.  Fabric Fabric – the mutual arrangement of grains, i.e. their position relative to one another. Fabric example: preferred orientation – elongate grains are often orientated in more or less the same direction (e.g. parallel to flow direction). – flattened pebbles are stacked one against the other, dipping upstream (imbrication) Current direction Biogenic sediments Carbonates  Carbonates composed of calcite (which makes up limestone) and dolomite. Limestones are deposited in warm, tropical, shallow-marine environments. Dolomite is not formed by marine organisms, but forms during diagenetic replacement of calcite. Jean-Marc Truchet/Tony Stone Worldwide  Carbonates - composition Grains – skeletal fragments of organisms, faecal pellets, coated grains (ooides). Micrite – carbonate mud. Cement – commonly calcite. Crinoid Broken Stem Peter Kresan Chemical sediments Evaporites  Evaporites inorganic precipitates from saline-rich waters (brines). Brines form from the evaporative concentration of salts in water, e.g. in a salt lake. The most common evaporite minerals are anhydrite, gypsum and halite.  anhydrite gypsum  Evaporites form in continental basins (salt lakes). form in marginal ocean basins or lagoons with restricted access to the main ocean. The bank of the Dead Sea, one of Earth’s saltiest bodies of water. It is nearly ten times saltier than the ocean. Credit: Nadav Lensky/Geological Survey of Israel. Organic sediments Coal  Coal Coal is derived from plant remains. Plant remains were deposited in delta environments coastal lagoons river flood plains Coal formed in vast swampy areas like the Everglades Swamp, Florida  Coal The plant remains are changed to coal by the diagenetic process of coalification. With burial and increasing heat and pressure the plant material (peat) changes to lignite (soft brown coal) bituminous coal (hard black coal) anthracite. These changes reflect increasing coal rank – which reflects an increase in the percentage of carbon in the coal. Coal Mining Australia Indonesia  SEDIMENTS AND SEDIMENTARY ROCKS Rock types  Definitions Detritus - disintegrated and broken fragments of pre-existing rocks that constitute the sedimentary particles. Terrigenous sediment – land-derived detritus Clastic sediment - sediment composed of fragments (clasts) of rocks and minerals. Provenance – the source area (area of erosion where the detritus was formed).  Sedimentary Rocks Sediments are the building blocks of sedimentary rocks. Sediments are diverse, as are the rocks made from them. 4 classes:  Clastic  Biochemical  Organic  Chemical Clastic Biochemical Organic Chemical Clastic sedimentary Sedimentary rock types Siliciclastic sedimentary rock: made up of grains of silicate minerals, mainly quartz (e.g. sandstone). Volcaniclastic sedimentary rock: dominated by detritus of volcanic rocks origin (e.g. tuff, lithified volcanic ash). Bioclastic sedimentary rock: broken and fragmented skeletons of animals (e.g. coquina, a shelly limestone). Biogenic sedimentary rock: produced directly by the activity of organisms (e.g. limestone). Organic sedimentary rock: consisting of organic material. Chemical sedimentary rock: produced by precipitation from water.  USGS Mt Pinatubo Deposition of a volcanic ash fallout layer Coquina – composed almost entirely of shells Siliciclastic sedimentary rocks  Conglomerate and breccia Coarse-grained sedimentary rocks in which the clasts > 2 mm in diameter. They are divided on the basis of clast shape into: Sedimentary breccia (angular clasts) clasts have not been transported far Conglomerate (rounded clasts) clasts have been transported sufficiently for rounding to occur Conglomerate – rounded clasts separated by sandy matrix Matrix Clast Breccia  Conglomerate and breccia Clast content may be: Monomict (single rock type) Polymict (variable rock types)  Conglomerate and breccia can be divided on matrix content into: clast-supported – little matrix, clasts are touching each other matrix-supported – much matrix, clasts float in the matrix Matrix- supported conglomerate Clast- supported conglomerate  Conglomerate and breccia Diamictites are matrix-supported conglomerates with a muddy matrix. Tillites are diamictites of glacial origin.  Sandstones Sedimentary rocks with a grain size between 0.063 - 2 mm (i.e. sand- sized). the dominant component is quartz, although feldspar and lithic grains (rock fragments) are also important.  Sandstones Some sandstones contain silt- to clay-sized particles (matrix) in the pore space. Arenites: < 15 % muddy matrix Greywackes: > 15 % muddy matrix  Sandstones Arenites are subdivided on mineral content into: Quartz arenite: > 95 % quartz Arkosic arenite (Arkose): > 25 % feldspar Lithic arenite: > 25 % lithic fragments Shown is a classification scheme for arenites.  Mudrocks Fine-grained sedimentary rocks made up of silt and clay (i.e. 1 cm thick Lamina - a layer of sediment < 1 cm thick Beds/laminae are deposited by a single depositional event (e.g. a flood or storm event). Bedding planes – beds are separated by bedding planes, i.e. the top and bottom surfaces of a bed.  Upper bedding plane Bed Lower bedding plane (sole)  Bedding thickness Beds are classified according to their thickness: Very thick bedded > 100 cm thick Thick-bedded 30-100 cm thick Medium-bedded 10-30 cm thick Thin-bedded 1-10 cm thick  Bedding morphology The geometry of beds is determined by the orientation of the bedding planes. Flat bedding - upper and lower bedding planes are parallel. Wavy bedding - the bedding surfaces are undulatory. Lenticular bedding - the bed pinches out laterally to form a lens.