Sedimentology Sedimentary ParticlesLecture 1

Jyoti KhatiwadaRoll no 10

types of sedimentary particles• Sediment is a naturally occurring material that is broken down by

processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice, and/or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea be deposited by sedimentation and if buried this may eventually become sandstone and siltstone, ( sedimentary rocks).

• Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.

Solid breakdown Particles

• Sedimentary deposits are assemblages of individual grains, or particles, which compose the framework of modern sand or mud deposits (beach, flood plain) and its lithified equivalent (sedimentary rock). The goal of this laboratory exercises is to provide you with an overview of some of the many type of particles commonly found in Sedimentary Rocks, from terrigenous and marine sediments.

• A. TERRIGENOUS/ BREAKDOWN PARTICLES. Terrigenous sedimentary particles can be divided into 2 groups (Friedman and Sanders, 1978):

• 1) solid breakdown products of older deposits and • 2) materials that are not solid breakdown deposits. • Group 2 consists of volcanoclastic materials and those transported in

water solution and deposited at the site of accumulation by biologic secretion or chemical precipitation.

Solid breakdown particles• Those eroded from the land are terrigenous particles and

fall into 2 groups:• a) inorganic terrigenous materials and • b) carbonaceous materials. Most terrigenous particles

come from bedrock. Inorganic terrigenous particles include: rock fragments, quartz, feldspar and heavy minerals originally derived from igneous or metamorphic rocks.

• Carbonaceous terrigenous particles include• 1) solid carbonaceous materials reworked from older strata,

and• 2) modern plant detritus. Breakdown particles are also

referred to as Siliciclastic.

Teachers slide solid breakdown products

• Inorganic particles =Rock fragments , Quartz, Feldspar, Layered lattic silicates , Heavy minerals , clay minerals and mica

• Particles not breakdown= Pyroclastic (erupted bombs blocks, tepras, etc) and Authegenic ( Skeletal debris, Silicious skeletal debris, Phosphatic skeletal debris, Non Skeletal Calcium carbonate debris, Evaporites)

• Clay mineral conversion ( feldspsr to Kaolinite ),(Montomorolite to clay minerals)

• Clastic sedimentary rocks such as breccia,conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris.

• Chemical sedimentary rocks, such as rock salt, iron ore, chert, flint, some dolomites, and some limestones, form when dissolved materials precipitate from solution

• Terrigenous sediments (siliciclastics) in the oceans are concentrated on continental margins (decreasing abundance into the basin) and in the deep sea, as red clay. Because sediments of continental margins are derived from land and sea, they are termed hemipelagic sediments- essentially they are pelagic sediments diluted by fluvial and Aeolian sediments. The deep sea red (often brownish) terrigenous sediments contain no or very rare calcareous microfossils.

particles that are not solid breakdown products of older sediment deposit

• Pyroclastic materials • Authigenic particles• Pyroclastic material is another name for a cloud

of ash, lava fragments carried through the air, and vapor. Such a flow is usually *very* hot, and moves *rapidly* due to buoyancy provided by the vapors. Pyroclastic flows can

extend miles from the volcano, and devastate life and property within their paths.

Authigenic particle –Non solid breakdown particle

• Authegenic = formed where found —used of mineral particles of rocks formed by crystallization in the place they occupy —opposed to allothogenic

• AUTHIGENIC. Authigenic sediments are those chemically precipitated from seawater. Common examples include manganese nodules and Glauconite (green sands).

• Precipitation of minerals on or within the sediments of the sea floor generally results from supersaturation of the element or compound required to form the mineral. Because authigenic mineral accumulation rates are often less than 1 mm/1000 years, resulting sediments are common only where terrigenous and biogenic accumulation rates are nearly zero. In many cases, crusts of authigenic minerals form where bottom currents prevent the accumulation of other sediments.

Examples of authegenic• Barite (BaSO4) occurs in crystalline or microcrystalline phases or as replacement

material in fecal pellets in deep-sea sediments. Barite concentrations average 1% in deep sea sediments, but can make up as much as 10% by weight of the carbonate-free fraction on the East Pacific Rise, where it is associated with hydrogenous iron oxide. Most (80%) of the elemental barite in the oceans enters through rivers, about 20% comes from hydrothermal vents

• Evaporite-Glauconite is a well-ordered K- and Fe-rich mica-structure clay mineral. It occurs as flakes or pellets, and may occur as infilling in foraminiferal shells and sponge spicules. It may occur in fissures in feldspars, as crusts on phosphorite nodules, and as replacement mineral in coproliths. The color is usually blue-green, but this depends on the original clay-type and chemical composition

• Marine Phosphates concentrations are typically very low within the euphotic zone of the oceans because phytoplanktons extract phosphate nutrients to photosynthesize organic matter. Vertebrates also concentrate phosphate into apatite, from which their bones are constructed.

• Organic-Rich Sediments is measured in sediment as total organic carbon (TOC) or particulate organic matter (POC) which in ocean water is primarily living organisms or the remains of dead organisms. Upon the death of an organism, its remains are subjected to chemical and bacterial degradation processes

The End

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