Part C: Types of Sedimentary RocksDetrital Sedimentary Rocks- Detritial sedimentary rocks are separated from Chemical and Biochemical Sedimentary Rocks as they are composed of: Rock fragments and particles cemented and compacted together.-Detrital rocks are also called Siliclastic because their main constituents are: a) Silicate Clay Minerals; b) Quartz.-This rock category is divided into different rock types according to grain/sediment size (examine Lab Book Figure 6.3 on page 131).-What can grain size reveal about the depositional environment?The larger the grain size, the greater the energy that existed. Gravels would accumulate in higher energy environments than clays.-Take your own notes on the different types of Detrital Sedimentary rocks:

a) Mudstone (Claystone, Shale, Siltstone)Particle Size: Clay to silt sized (sediments are not identifiable without magnification).Depositional Environment: Gradual settling in quiet environments (lakes, floodplains, lagoons, deep-ocean basins) Strength: Weak, as during compaction clay and silt particles align closely and in doing so reduce pore spaces. This prevents cementation from occurring (usually only weak cementation occurs). Lack of pore spaces makes shale and other mudstones impermeable to liquids= aquifers, oil/gas reserves.Breakage: Shale has fissility; mudstone breaks into chunks or blocksOther Characteristics: Siltstone lacks fissility and is made of silt and small amounts of clay.

b) Sandstone (Quartz, Arkose, Wacke)Particle Size: SandDepositional Environment: A variety, with particle size, shape and composition indicating where.Sorting: Best sorting by wind,

then waves, then rivers. Poorly means short transportation and rapid deposition.

Roundness: Streams, wind or waves move particles they hit together=become round with distance, time or repetition of disturbance. Angular grains not transported far or were transported by a different mechanism (glacier)Composition: Length or erosion and number of transports reflected by what mineral grains are left. Silica is very resistant.Types:i) Quartz Sandstone: Quartz is the dominant mineral, well sorting/rounding indicates long transportation or many repetitions.ii) Arkose Sandstone: Large quantities of feldspar are present (quartz and biotite too=granitic origin), poor sorting/angular grains indicates short transportation, dry climate (minimal chemical weathering of feldspar) and rapid deposition/burial. iii) Wacke Sandstone: Quartz, feldspar and abundant rock fragments and matrix. Poor sorting/angular grains indicate short transportation and rapid deposition. E.g. Turbidity current.

*The Folk Classification System for Sedimentary Rocks takes the ratio of mud to sand very seriously…

c)

Conglomerate and BrecciaParticle Size: Gravel. Large enough to indicate parent material. -Differentiate between Conglomerate and Breccia

depositional environments based on their particles:Both contain large, poorly sorted particles=high energy environments for deposition.

Conglomerate particles are rounded and breccia particles are angular, indicating some and no/minimal transportation.

Chemical Sedimentary Rocks-Are the product of materials carried in solution when it precipitates to form chemical sediments.-Precipitation occurs as a product of evaporation (crystalline texture) and the chemical activity of organisms like corals (clastic texture).

a) LimestoneComposition: Calcite (CaCO3), so will react completely with acidic water through dissolution (powder the rock, drop HCL on).Formation Process: Inorganic or biochemical (shells).Types:i) Organic Limestone: Made up of the cemented remains of shells (corals, etc). Examples include fossiliferous limestones like coquina (visible shells) and chalk (microscopic shells).ii) Inorganic Limestone: Chemical changes, water temperature or microbial activity super saturate water with calcite=precipitates. Examples include travertine limestone in caves and oolitic limestone in shallow marine waters .

b) Chert (Flint, Jasper, Agate)Composition: Silica (Si02)Formation Process: Inorganic (precipitation from water results in nodules; decay of volcanic ash); Biochemical (silica skeletons of diatoms and radiolarians results in tabular layers)

d) Evaporites-Evaporation results in the precipitation of minerals (halite, gypsum) out of solution.

Coal-Take your own notes on coal formation from text pages 155 to 166.