SEDIMENTS Flashcards
4 classes of sedimentary rocks
= Clastic – Made from weathered rock fragments (clasts)
= Biochemical – Cemented shells of organisms
= Organic – The carbon-rich remains of plants
= Chemical – Minerals that crystallize directly from water
what 5 process do Clastic sedimentary rocks reflect
= Weathering – Generation of detritus via rock disintegration
= Erosion – Removal of sediment grains from rock.
= Transportation – Dispersal by wind, water, and ice.
= Deposition – Accumulation after transport stops.
= Lithification – Transformation into solid rock
what are Clastic Sedimentary Rocks classified on the basis of
= Clast (grain) size
= Clast composition
= Angularity and sphericity -> reflects degree of transport
= Sorting -> well sorted = uniform grain size
= Character of cement -> Dissolved ions slowly crystallize in (and fill) pores e.g. Quartz, Calcite
what is meant by maturity of Clastic Sedimentary Rocks and its 2 types
the degree of “processing.”
= Textural maturity – Degree of roundness and sorting
= Mineral maturity – Degree of unstable mineral removal
how does Time and transport cause sediment evolution
- Texture: Average grain size decreases ; roundness and sorting increases
- Composition: Unstable minerals decreases, Stable minerals increases
types of Clastic Sedimentary Rocks
- Coarse clastics - gravel-sized clasts (Breccia = angular clasts + Conglomerate = rounded clasts)
- Sandstone – sand-sized particles (quartz = dominant mineral)
- Fine clastics - silt and clay (mud) (only deposited in non-agitated water)
types of Biochemical Sedimentary Rocks
- Biochemical limestone – Made from CaCO3 shell remains
- Biochemical chert – Cryptocrystalline quartz rock (Formed from opalline silica (SiO2) skeletons)
types of organic rocks
- Coal – Altered remains of fossil vegetation
- Oil shale – Shale with heat-altered organic matter
types of Chemical Sedimentary Rocks
- Evaporites – Created from evaporated seawater
- Travertine – CaCO3 precipitated from ground water where it reaches the surface (Thermal (hot) springs -> Tufa, Caves -> speleothem)
- Dolostone – Limestone that has been chemically modified by Mg- rich fluids
- Replacement chert (SiO2) – Nonbiogenic in origin (many varieties e.g. flint, jasper, petrified wood, agate)
Why does bedding form (sedimentary rocks arranged in planar, horizontal)
- caused by changing conditions during deposition - Energy conditions -> grain size
- may also reflect non-deposition or erosion
*series of beds = strata, sequence of strata = formation
5 types of sedimentary structures
- strata / formation - series of beds
- bedforms - Water flowing over loose sediment (Asymmetric ripples = Unidirectional flow, Symmetric ripples = Wave oscillation)
- Dunes – Similar to ripples except much larger
- Cross-beds – Created by ripple and dune migration
- Graded Bed – Bedding layer that fines upward
How do graded beds form
- Disturbance to submarine slope sediment -> Turbidity current
- As current wanes, water loses velocity and sediments settle
- Coarsest material settles first, medium next, then fine
*Multiple graded-bed sequences = turbidites
3 types of Bed-Surface Markings in soft sediment
- Mudcracks - Indicate alternating wet and dry conditions
- Scour marks – Troughs eroded in soft mud by current flow
- Fossils – Evidence of past life
what are Depositional Environments and 2 types
Locations where sediment accumulates - strongly linked to sea level
- Terrestrial environments – above sea level e.g. glacial till (poorly sorted gravel, sand, silt, and clay), Mountain streams, Alluvial fan, rivers, sand dunes, lakes
- Marine environments – at or below sea-level e.g. Deltas, Shallow marine, Coastal beaches, Shallow water “carbonate environments” – Tropical, Deep marine
what is Sedimentary basin- sediment-filled depression important for
=Coal
=Petroleum
=Natural gas
=Uranium
how is Sedimentary deposition strongly linked to sea level
- Transgression – Flooding due to sea level rise
- Regression – Exposure due to sea level fall - tied to erosion; less likely to be preserved
whats Diagenesis and its types
changes occurring during the conversion of sediment to sedimentary rock
= Bioturbation
= Lithification
= Dissolution
= Mineral precipitation
= Pressure solution
