Dynamic Surface L1 Flashcards
What is sediment?
Solid fragmented material that is either eroded from pre-existing rock, chemically precipitated from solution or secreted by organisms which accumulates as layers in loose unconsolidated form.
What is an example of sediment?
Mud, sand
What is a sedimentary rock?
A rock that results from the consolidation of sediment and diagenesis of minerals.
What is a crystalline rock?
Igneous and metamorphic rocks that form as a result of cooling magma etc
What kind of rock is a sedimentary rock?
Fragmentary
What is the economic importance of sedimentary rock?
Oil and gas
Coal
Mineral deposits
Sand, gravel, building materials
Aquifers
Geothermal energy reservoirs
What is a sedimentary facies?
A body of rock with distinct characteristics that reflect the conditions of deposition. Can be carried out on any scale from grain type to large sedimentary structures.
Which 2 features of oceans define what sediments are produced and preserved?
Latitude
Water depth
Which two broad groups can sedimentary rocks be classified into?
Clastic and non-clastic
What is a clastic rock?
A rock made up of fragments of pre-existing rock
What is a volcaniclastic rock?
The products of volcanic eruptions or the result of the breakdown of volcanic rocks.
What is a terrigenous clastic rock?
Rock that is generated from the land
What is a carbonate rock?
Rocks that are mostly non-clastic, formed from shells and skeletons of organisms.
What are 6 ways we can classify sedimentary rocks?
Grain size
Grain shape
Grain roundness/sphericity
Grain sorting
Compositional classification
Maturity of sediments
Define mud in terms of grain size.
Sediment where you cannot discern individual grains with the naked eye.
Define sand in terms of grain size.
Sediment where the grains are visible with the naked eye but less than 2mm on its longest axis
Define clasts in terms of grain size.
Larger particles, usually pebbles
What is the matrix?
The fine-grained material between grains and clasts in sediments and rocks with a bi-or higher modal distribution
What is cement?
Distinct from the matrix - precipitated and grown in pore spaces after deposition
What can the grain shape tell us about the sedimentary rock?
How long the grains have been in the depositional system
What is an equant grain?
Grains that have equally spaced fracture planes in all directions (e.g. a cube/sphere)
What is a discoid/oblate grain?
Grains with one axis shorter than the other two (e.g. a thin cube/sphere)
What is a prolate grain?
Grains that are rod-shaped (e.g. long, thin cylinders/cuboids)
What are the 4 types of grain shape?
Equant
Prolate
Discoid/oblate
Bladed
What is a bladed grain?
Grains that are long and thin (e.g. a long, thin cuboid/cylinder)`
What does grain roundness say about the transport of a grain?
The longer the grain has been transported, the higher roundness it will have.
How can the roundness of a grain infer the distance from the source?
Increasing distance from the source = increasing roundness
Name the stages of roundness from “well rounded” to “very angular.”
Well rounded
Rounded
Sub-rounded
Sub-angular
Angular
Very angular
What are the two categories of sphericity?
Low sphericity
High sphericity
When talking about the texture of a rock and its grains, which characteristics are being described?
Size, sorting, roundness and sphericity
What is grain sorting?
The grain size distribution
What is a well-sorted rock?
A rock with a very small grain size distribution (grain sizes are very similar)
What is a poorly sorted rock?
A rock with a large grain size distribution (grain sizes are highly differing)
What are the main minerals of sedimentary rocks?
Quartz, feldspar, calcite and micas
What is the Pettijohn system?
A classification scheme that determines the relative proportions of quartz, feldspar and lithic fragments in a sedimentary rock
What are the 3 components of sediment maturity?
Mineralogy
Texture
Size
How does mineralogy tell us about sediment maturity?
The more mature a sediment is, the higher the proportion of quartz, the most resistant component, there will be
How does texture tell us about sediment maturity?
The more rounded the grains are, the longer they will have been rolled and abraded against each other
How does size tell us about sediment maturity?
The smaller the grains, the further they may have
been transported from source and the lower the velocity of the depositing flow
What are the characteristics of a supermature rock?
< 15% mud content (arenite)
Well sorted
Rounded grains
What are the characteristics of an immature rock?
> 15% mud content (wacke)
