stratigraphy Flashcards
what is lithostratigraphy based on?
– Lithostratigraphy is based on rock boundaries
what is biostratigraphy based on?
– Biostratigraphy is based on fossil boundaries
what is chronostratigraphy based on?
– Chronostratigraphy has definite time boundaries using the stratigraphical time column.
this column is made by specific events including extinctions and from fossil collection
what is lithostratigraphy?
it is the description, comparison & correlation of layered rock units in space & time
it is the basis for all geological exploration
what does the word formation mean?
• The word formation has a strict meaning, it is the base unit
• The Formation is the basic unit, which:
– Is internally homogenous (mostly)
– Has clear boundaries
– Can be mapped out (at scale of 1:10,000 : scale traditionally used for mapping)
what do geological maps show/define?
maps define the lateral extent, as they appear at the surface, of lithostratigraphical units (i.e. formations)
time tools that are independent of rock type allow correlation by establishing time lines. these are created by using:
– Fossils (evolution/extinction)
– Events (global/regional footprint)
what is diachronism?
when the deposit may be lithologically identical, but of differnet ages in seperate places
what are most fossils and why?
- Most fossils are:
- Marine in origin
- Have hard parts
- Why?
- Marine organisms more likely to be buried
- Soft parts decay
- Rapid burial is best
- On land organisms are normally eroded before they have time to be fossilised
define biostratigraphy
is the method of subdividing the rock record into units based on fossils
what is biostratigraphy based on?
• Based on ‘Principle of Faunal and Floral Succession’:
– Life evolves, becomes extinct & leaves a record of existence as a series of fossils in order of appearance
– Some organisms (guide fossils) are better suited than others for global correlation
what six points make a good guide fossil?
Essential:
• Free moving
• Widespread
• Rapidly evolving
Desirable:
• Abundant
• Readily preserved
• Easily recognised
define chronostratigraphy.
- Considers stratigraphy as time passed using the stratigraphical column that we have been told to learn. This column has been internationally agreed.
- Chronostratigraphical units (e.g. Systems) have isochronous boundaries, defined by biozones or events
- Radiometric dating of these provides an absolute timescale
what is this called?
when?
info?

trilobites (trilo = three lobes)
• Cambrian–Carboniferous
- Large number of species & habitats
- Hard exoskeleton with jointed limbs
what is this called?
when?
info?

grapolites
• Cambrian–Devonian in age
- Floating, branched colonial organisms
- Many different types: good guide fossils
what is this?
when?
info?

Brachiopods
• Cambrian–Recent: dominant in Palaeozoic
- Great diversity in fossil record
- Bivalved shell, mostly attached to seafloor
what is this?
when?
info?

Corals
• Cambrian–Recent
- Major extinction end Permian: Palaeozoic types differ from Mesozoic
- Can be compound (colonial) or solitary

what is this?
when?
info?

Bivalves
• Ordovician-Recent: dominant Mesozoic–Recent
- Two valves or shells: differ from Brachiopods
- Infaunal (equivalve): equal valves: buried into sand as it has two equal valves
- Epifaunal (inequivalve): often unequal valves: a curved valve and a flat edge it can’t bury itself into the sand

what is this?
when?
info?

ammonites
• Devonian–Cretaceous
- Chambered shells
- Rapid evolution; great diversity
- Superb guide fossils

what is this?
when?
info?

gastropods
- Ordovician-Recent
- most common in Cenozoic
- land, freshwater, sea
- Poor guide fossils overall as they have had a very slow evolution
Conical shells are more typical
what is this?
when?
info?

Echinoderms
• Cambrian–Recent
- Shell made of calcite crystals
- Based on five-ray symmetry
- Stalked crinoids (usually Palaeozoic)
- Sea urchins (usually Mesozoic)
what is stratigraphy?
it is the interpretation of rock units as sequences of events in earth history
stratigraphy is the interpretation of rock units as sequences of events in earth history. How do we establish the sequence?
we use:
- sequncing tools (superpositon, way up, etc)
- time tools ( litho-, bio, and event stratigraphy)
stratigraphy is the interpretation of rock units as sequences of events in earth history. how do we interpret the sequence?
we use the primary tool actualism (uniformitarianism)














