Sedimentology and Palaeontology Lecture 6: Biostratigraphy and Microfossils

Question 1

Define Biostratigraphy

Answer 1

The use of fossils to define biozones, stratigraphical ranges of taxa that correlate with specific periods of geological time

Question 2

Define a Biozone and how they are determined

Answer 2

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

Question 3

Define a total range biozone

Answer 3

Total range biozone
- Defined by total range of a
single species

Question 4

Define a concurrent range biozone

Answer 4

Concurrent-range biozone
- Defined by overlapping
ranges of certain species

Question 5

Define a consecutive range biozone

Answer 5

Consecutive-range
biozone
- Defined by the range of a
single chronospecies (i.e.
species B in the sympatric
lineage of species A-B-C)

Question 6

Define a partial range biozone

Answer 6

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

Question 7

Define an acme biozone

Answer 7

Acme biozone
- Defined by
superabundance of a
certain species

Question 8

Define an assemblage biozone

Answer 8

Assemblage biozone
- Biozone defined by the
overlapping ranges of
multiple species

Question 9

List the principal biostratigraphical fossils

Answer 9

-Trilobites – Cambrian, some
Ordovician and Devonian

• Nautiloids – Early Ordovician
• Ammonoids – Devonian – Cretaceous
• Bivalves + gastropods – Cenozoic
• Graptolites – Ordovician - Silurian

Question 10

Describe Graptolites

Answer 10

Graptolithina: diverse
group of stick-like fossils
preserved as flattened
carbonised films

• Cambrian -
  Carboniferous
• Extremely abundant in
  Lower Palaeozoic black
  shales

Question 11

Define Macrofossils

Answer 11

Macrofossils are mostly too big for use in subsurface
exploration: borehole drills obliterate them beyond all
diagnosis

Question 12

Define Cuttings

Answer 12

pieces of rock excavated from the well - can
contain thousands of microfossils in a few grammes

Question 13

Define Microfossils

Answer 13

Microfossils are generally
considered as fossils measuring
less than 5 mm, be it a
complete organism or a
component of a larger one

Question 14

What are the two types of Microfossils

Answer 14

inorganic-walled
* (e.g. calcium carbonate;
silica; phosphate)

organic-walled
* (=palynomorphs - a microscopic fossil composed especially of pollen or spores.)

Question 15

Define Palynomorphs

Answer 15

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,

Question 16

Describe Foraminiferans (‘forams’)

Answer 16

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

Question 17

Describe Coccoliths

Answer 17

Calcareous nannoplankton
responsible for chalk deposits

• Triassic – Cretaceous
• Very useful zone fossils:
• Very abundant from Jurassic
  onwards
• Provide biozones from Jurassic

Question 18

Describe Chitinozoans

Answer 18

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

Question 19

Describe Dinoflagellates and their anatomy

Answer 19

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

Question 20

Define spores

Answer 20

Spores: the reproductive
agents of fungi,
gymnosperms and other
primitive plants

Question 21

Define Pollen

Answer 21

Pollen: ‘male’
reproductive agents of
flowering plants