Sedimentary defined
- rocks formed at the surface of the earth either in water or on land
- produced by movement of sediments, precipitation from solution and organic remains
- layered accumulations of sediments
- cover 75%-80% of the Earth’s land
- environments: continental, transitional (delta/intertidal), Marine
Bedding
- primary compositional layer in a sedimentary/volcanic rock
- most important discontinuity in a sedimentary/volcanic rock sequence
- Types: page Q04-2-7
- vary in size and can be folded/tilted due to tectonic activity
strata
horizontal planes and layers
lithification
-sediments are converted into rocks through cementation and compaction where the common cementing materials of quartz, calcite, and iron oxides
Particle shapes
angular: no evidence of wear sub-angular: shows some wear sub-rounded: considerable wear rounded: only some flat faces remain well-rounded: well rounded
Particle sorting
well sorted: poorly graded, particles occur in narrow size range ex: beach sand
poorly sorted:well graded, particles occur in near equal amounts in all size range ex: river channel/glacial deposits
Clastic Sedimentary Rocks
-Mechanically-formed sedimentary rocks
derived from the chemical and mechanical breakdown of pre-existing rock
-often contain rock frags (ortho feldspar, quartz, and clay) and are classified on grain size
sedimentary classifications
- classified by source of their sediments and by methods of development:
- mechanically-formed
- chemically-formed
- organically-formed
conglomerates
- mechanically formed
- consolidated gravels with part size >2 mm
- defined by cementing material
breccia
- mechanically formed
- consolidated gravels with part size>2 mm
- particles are sharp
- defined also by cementing material
sandstones
- mechanically formed
- consolidated sand (.062-2 mm)
siltstone
- mechanically formed
- particls between .002 to .063 mm
shale
- mechanically formed
- consolidated mud (<.0062 mm)
- rich in organic matter
mudstone
- mechanically formed
- constituents originally mud (<.0625 mm)
- need microscope for grains
strength and resistance to weathering (mech formed)
type strength res. to weathering
mudstone small weak
shale
siltstone
sandstone
conglomerate large high
and breccia
Chemically formed sedimentary rocks
-formed when minerals in solution oversaturate and precipitate
-2 environments: marine and evaporating
Halite
Limestone
Gypsum
Dolomite
limestone
- chemically formed
- primarily calcite
- accumulation of fossilized remains of organisms in sea
- important for fertilizer and building (contains C, N, K, P)
Dolomite
- chemically formed
- contains mostly dolomite
- aka dolostone
Clastic Sedimentary Rocks in HK
conglomerates, sandstones, and mudstone
heterogeneity
diverse combination
