Sedimentology and Palaeontology Lecture 6: Biostratigraphy and Microfossils Flashcards
Define Biostratigraphy
The use of fossils to define biozones, stratigraphical ranges of taxa that correlate with specific periods of geological time
Define a Biozone and how they are determined
Biozones are defined by the stratigraphical ranges of fossils or
groups of fossils
- The first and last appearances of fossil taxa are therefore
important dates: - FAD: First Appearance Datum
- LAD: Last Appearance Datum
Define a total range biozone
Total range biozone
- Defined by total range of a
single species
Define a concurrent range biozone
Concurrent-range biozone
- Defined by overlapping
ranges of certain species
Define a consecutive range biozone
Consecutive-range
biozone
- Defined by the range of a
single chronospecies (i.e.
species B in the sympatric
lineage of species A-B-C)
Define a partial range biozone
Partial-range biozone
- Defined as the range a of
species between the FAD
and LAD of other species
(e.g. species B between
the LAD of species A and
FAD of species C
Define an acme biozone
Acme biozone
- Defined by
superabundance of a
certain species
Define an assemblage biozone
Assemblage biozone
- Biozone defined by the
overlapping ranges of
multiple species
List the principal biostratigraphical fossils
-Trilobites – Cambrian, some
Ordovician and Devonian
- Nautiloids – Early Ordovician
- Ammonoids – Devonian – Cretaceous
- Bivalves + gastropods – Cenozoic
- Graptolites – Ordovician - Silurian
Describe Graptolites
Graptolithina: diverse
group of stick-like fossils
preserved as flattened
carbonised films
- Cambrian -
Carboniferous - Extremely abundant in
Lower Palaeozoic black
shales
Define Macrofossils
Macrofossils are mostly too big for use in subsurface
exploration: borehole drills obliterate them beyond all
diagnosis
Define Cuttings
pieces of rock excavated from the well - can
contain thousands of microfossils in a few grammes
Define Microfossils
Microfossils are generally
considered as fossils measuring
less than 5 mm, be it a
complete organism or a
component of a larger one
What are the two types of Microfossils
inorganic-walled
* (e.g. calcium carbonate;
silica; phosphate)
organic-walled
* (=palynomorphs - a microscopic fossil composed especially of pollen or spores.)
Define Palynomorphs
A catch-all term for organic-walled microfossils including (but
not restricted to):
- Dinoflagellates
- Chitinozoans
- Spores
- Pollen
All can be extracted from rocks using acids that would
damage other types of microfossil,
Describe Foraminiferans (‘forams’)
Heterotrophic single-celled
eukaryotes with globular
CaCO3
tests
- Abundant in marine
Ediacaran – Recent strata,
and large enough to be seen
with low-power
microscopes
- Primarily used for dating the
Cenozoic and some parts of
the Permian
Some Forams are pelagic but most are benthic living
epifaual or infaunal existences
on the sea floor
Describe Coccoliths
Calcareous nannoplankton
responsible for chalk deposits
- Triassic – Cretaceous
- Very useful zone fossils:
- Very abundant from Jurassic
onwards - Provide biozones from Jurassic
Describe Chitinozoans
mystery microfossil, assumed to be the egg-case of
an unknown Palaeozoic metazoan
Confirmed stratigraphical range of Cambrian – Devonian,
with hundreds of species known by 470 Ma
Describe Dinoflagellates and their anatomy
Photosynthetic unicellular algae responsible for red tides
- Commonly possess thickened thecae
- Flagellae, or ‘whips’ extend from the cingulum and are used
for movement
Cysts underlie the
thecae
- Confirmed
stratigraphical range of
Silurian – Recent - Useful for dating some
parts of the Mesozoic,
and Cenozoic
Define spores
Spores: the reproductive
agents of fungi,
gymnosperms and other
primitive plants
Define Pollen
Pollen: ‘male’
reproductive agents of
flowering plants
