Module 2.2: Rocks (Sedimentary)

Sediment

An accumulation of loose mineral grains or very small fragments of rocks, such as boulders, pebbles, sand, silt, or mud, that are not cemented together

Sedimentary rocks

Rocks that form either by cementing together rock fragments or by precipitation of mineral crystals out of water solutions

Weathering

Process that fractures and dissolves the rock, creating sediment and dissolved components

Mechanical weathering

Physical disintegration of breaking up rock into smaller pieces

Frost wedging

Type of mechanical weathering where water seeps into cracks of rocks, which freezes and expands, and then exerts pressure and causes rocks to break apart

Thermal expansion

Type of mechanical weathering that involves the expansion of solid materials when heated

Exfoliation

Type of mechanical weathering where water erodes rocks in parallel layers due to pressure release

Chemical weathering

Type of weathering that alters a rock’s chemistry, changing it into different substances

Dissolution/hydrolysis

Type of chemical weathering which involves the breakdown of rocks and minerals through their interaction with water and acidic substances

Dissolution/hydrolysis

Type of chemical weathering that turns plagioclase into kaolin

Oxidation

Type of chemical weathering which involves minerals, particularly those containing iron, react with oxygen in the presence of water

Oxidation

Type of chemical weathering that turns pyroxene into hematite

Erosion

• Process that carries away the products of weathering as it moves rock or soil particles

• Comes from an old word meaning “eat away”

Gravity, ice, organism, water, and wind

The five agents of erosion

Sediment transport

The movement of sediment particles as they get deposited in other areas

Ice, water, and wind

The three agents of sediment transport

Suspension

Sediment transport that involves fine particles carried within the fluid

Saltation

Sediment transport that refers to the bouncing motion of medium-sized particles

Traction

Sediment transport that involves the rolling or sliding of large particles along the bed

Poorly sorted to well sorted

In clast sorting, short distance and long distance means?

Angular to rounded

In clast roundness and sphericity, short distance and long distance means?

Deposition

Process that accumulates sediments from large source regions

Higher energy environments

In terms of deposition, larger sediments are deposited where?

Diagenesis

• Process of transforming sediments into rocks through physical, chemical, and biological processes

• Modification of the texture and mineralogy of the rock

Compaction

• A diagenetic process wherein sediments are squeezed together due to the weight of overlying layers

• This leads to decrease in porosity but an increase in density

Cementation

• A diagenetic process wherein minerals precipitate from fluids within the pore spaces of sediments, binding the grains together

• Further reduces porosity and increases the cohesion of the sediment

Detrital or clastic

Sedimentary rocks consisting of cemented-together detritus derived from the weathering of pre-existing rock (detritus)

Non-detrital or chemical

Sedimentary rocks are made up of minerals that precipitate directly from water solution (chemical sediment)

Breccia

Detrital sedimentary rocks with grain size of 2mm or greater, and have clasts that are angular

Breccia

Identify the sedimentary rock

Breccia

Identify the sedimentary rock

Conglomerate

Detrital sedimentary rocks with grain size of 2mm or greater, and have clasts that are rounded

Conglomerate

Identify the sedimentary rock

Conglomerate

Identify the sedimentary rock

Sandstone

Detrital sedimentary rocks with grain size of 1/16mm to 2mm, classified according to the amount of minerals in the rock

Arkose sandstone

Sandstone with >25% feldspar

Quartz sandstone

Sandstone with >90% quartz

Lithic sandstone

Sandstone with >5% lithic fragments

Arkose sandstone

Identify the sedimentary rock

Arkose sandstone

Identify the sedimentary rock

Quartz sandstone

Identify the sedimentary rock

Quartz sandstone

Identify the sedimentary rock

Lithic sandstone

Identify the sedimentary rock

Lithic sandstone

Identify the sedimentary rock

Siltstone

Detritral sedimentary rocks with grain size of 1/256 to 1/16mm

Siltstone

Identify the sedimentary rock

Siltstone

Identify the sedimentary rock

Claystone

Detritral sedimentary rocks with grain size less than or equal to 1/256mm

Claystone

Identify the sedimentary rock

Claystone

Identify the sedimentary rock

Limestone

• Non-detrital sedimentary rocks made up of 90% biochemical sediment and 10% chemical

• It is the most abundant sedimentary rock.

Limestone

Identify the sedimentary rock

Limestone

Identify the sedimentary rock

Coquina

Non-detrital sedimentary rock composed mostly or wholly of biochemical shells

Coquina

Identify the sedimentary rock

Coquina

Identify the sedimentary rock

Chalk

Type of limestone which is more porous and is made almost of entirely hard parts of microscopic organisms

Chalk

Identify the sedimentary rock

Chalk

Identify the sedimentary rock

Chert

• Non-detrital rock made up of a siliceous rock

• Forms from the recrystallized skeletons of animals (single-celled radiolarians and glass sponges) or plants (diatoms, silicoflagellates)

Chert

Identify the sedimentary rock

Chert

Identify the sedimentary rock

Rock salt (halite)

• Non-detrital rock of fine to coarse crystals made up of salt (NaCl)

• Formed through the drying of a lagoon which supersaturates and precipitates out

Rock salt (halite)

Identify the sedimentary rock

Rock gypsum

• Non-detrital rock of fine to coarse crystals made up of hydrated calcium sulfate (CaSO4 . H2O)

• Formed through the drying of a lagoon which supersaturates and precipitates out

Rock gypsum

Identify the sedimentary rock

Peat and coal

• Non-detrital sedimentary rocks of biochemical composition that come from plant remains

• Commonly used in fossil fuel

Sandstones and shales

The clastic rocks that cause the formation of peat and coal

Lignite coal → Bituminous coal → Anthracite coal

The life cycle of anthracite

Anthracite

Hard, compact variety of coal with a high carbon content and submetallic luster