2.2 Stratigraphy and Cross Sections Flashcards
Stratigraphy
A branch of geology dealing with the order and succession of rock strata, their occurrence, sequence, lithology, composition, fossils, and correlation
Stratification
A structure produced by deposition of sediments in beds or layers (strata), laminae, lenses, wedges, and other essentially tabular units
Stratified
Arranged in or composed of strata or layers
Stratigraphic sequence/succession
Refers to the original succession of stratified rocks
Steno’s Principles
- Principle of original continuity
- Principal of original horazontality
- Principle of superposition
- Principle of cross-cutting relationships
Principle of original continuity
Layers are continuous and end only by thinning, lithological transition, or a abutment against a barrier
Principle of original horizontality
When sediments are deposited the beds are horizontal
Principle of superposition
any new sedimentary layer must be added on top pf existing layers
principle of cross-cutting relationships
If a body or discontinuity cuts across a stratum, it must have formed after that stratum
Interpretation
Interpretation must rely on available data
- Site data is complete
- Interpretation is always required
Unconformities
A stratigraphic break
Angular conformity
an erosional surface that truncates older, tilted sedimentary layers
Disconformity
A break in a sedimentary sequence which does not involve a difference of inclination between strata on each side of the break
Nonconformity
Sediments are deposited on top of an eroded surface of igneous or metamorphic rocks
Marker Beds
Bed of rock strata that are easily distinguished and are traceable over a long horizontal distance
Fossils
- Limestone’s are rich in fossils
- Shale’s often have preserved fossils
- Sandstone’s sometimes have fossils
- They represent life in former times
Evolution
- Life evolve from simple to more complex forms
- Faunal successions and stratigraphic sequences are in the same order
Mapping Unit
Used to group deposits of similar age, materials, and appearance into formations
Mapping Units
Bed: A lithologically distinct layer (not normally named unless it is a marker bed) - the smallest recognizable stratigraphic unit
Member: Also a lithologically distinct layer and part of a formation
Formation: Primary units used to map in geology. Range in scale from cm to km - must have a sufficient extent to be useful in mapping.
Group: Two or more formations that share certain lithological characteristics.
