Sedimentary Rocks and Processes Flashcards
What is sediment?
Particles transported by water, ice, wind, and gravity.
What is stratification/bedding?
The arrangement of sedimentary particles in layers
What is a stratum?
A distinct layer of sediment
What do you call the top and bottom surfaces of a bed?
The bedding plane
What are the 2 main types of sediment/
Clastic (‘rock’) and non-clastic
What are the 2 main types of non-clastic sediment?
- Chemical precipitates
- Biogenic sediment (made from plants or animals)
What are the 4 sub-categories of clastic sediment in size order?
Gravel
Sand
Silt
Clay
How is sediment sorting described?
Poorly sorted (large range) or well sorted (similarly sized particles)
What is till?
Glacial sediment
How does water speed differentiate sediment?
Faster flowing water can transport larger/heavier particles
- As water slows, heavier particles are deposited first and lighter ones carried further
What is roundness?
A measure of the sharpness of the edges of a particle
What is sphericity?
A measure of how similar a particle’s shape is to that of a sphere
Used together, what can sorting, roundness and sphericity tell us?
About the environment sediment was transported and deposited in
What is graded bedding? What does it show?
A bedding in which particles are deposited mostly by size with the coarsest at the bottom
- Shows a change in energy of the depositional system over time
What is cross bedding? What does it show?
Inclined beds of sediment.
- Shows dominant wind directions
What is diagenesis?
Sediment becoming rock ( a collective term for all processes including compaction and chemical processes )
What is lithification?
The overall process for creating sedimentary rock
What is the difference between lithification and diagenesis?
Lithification is the overall process of creating sedimentary rock.
Diagenesis is the collective term for all chemical, physical, and biological processes that cause lithification.
What is compaction as a diagenesis process?
The weight of an accumulating sediment forces the grains together and the pore space is reduced.
What is cementation?
Substances dissolved in water precipitate to form a cement that binds sediment grains together
How do cementation and compaction work together?
Water being squeezed out by compaction allows chemicals to precipitate and cement.
What is recrystallisation?
Less stable minerals recrystalise into more stable forms
What is dissolution?
When some minerals are dissolved during burial
Name 4 common clastic sedimentary rocks.
Conglomerate, Breccia, Sandstone, Mudstone/Shale
What are the 4 vague categories of sedimentary structures?
- erosional
- depositional
- biogenic
- post depositional
What type of rock is coal?
A biogenic sedimentary rock
How is coal formed/
Plant remains accumulate and form peat which is compressed to become coal
How are erosional structures formed?
Aqueous flows run over recently deposited sediment and gouge out depressions which are usually then infilled by sediment from the flow
What are the two most notable erosional structures?
Flute marks (asymmetric dips, wider upstream), Groove marks (ridges)
What do depositional structures depend on?
Flow velocity, flow depth, grain size
What are some examples of depositional structures?
Ripples, dunes, cross stratification
What are biogenic structures?
Structures left by animals such as burrows
Name two types of biogenic structures.
Ichnofacies, Bioturbation
What is an ichnofacie?
Trace fossil left by something like a burrow or feeding structure
What are bioturbations?
Shapes/erosions in sediment caused by things like footprints
Name two post-depositional structures?
Mud cracks, raindrop depressions
What is an evaporite?
A rock formed from salts produced by evaporation
What makes biogenic sediment bioclastic sediment?
When the remains of plants/animals are then broken and scattered
What is deep sea ooze?
Fine deep sea mud formed of skeletal material
What are the two types of deep sea ooze?
Calcareous ooze is made from material with more than 30% calcium carbonate
Siliceous ooze is made from material that’s mostly silica
What are stromatolites? How are they formed?
Algae reef systems, formed incrementally as algae deposit calcium in laminations
What are BIFs?
Banded iron formations, iron concentrations in layers
What is limestone?
Rocks formed from the deposition of calcium carbonate
What is oolitic limestone?
Limestone containing 0.5-2mm spherical grains of carbonate, shaped when these particles roll around in tidal environments
What is chalk formed from?
Compacted carbonate shells of coccolithophores
