Lecture 9 Trace Fossils

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Lecture 9 Trace Fossils
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Ichnology is the study of the behaviour of
extinct organisms by examination of their traces,
tracks, burrows, borings etc. These are left in
sediments and or hard substrates and may
subsequently preserved as trace fossils. They
were produced by the activity of animals (usually
invertebrates but sometimes vertebrates). Many
animals such as worms, containing soft tissues
and no hard skeletal tissue, are known only from
trace fossils, as after death the animal decays
and the body is not preserved. Trace fossils are
most commonly represented in the geologic record
by features formed through animal activity in a
substrate of some sort, such as sediment, rock,
or wood. These features include burrows, tracks,
trails, and borings.

• Burrows are excavations made into an
  unconsolidated substrate.
• Borings are excavations made into a
  consolidated substrate, which could include rock
  or wood.
• Tracks are imprints on a sediment surface by an
  animal with legs.
• Trails are imprints on a sediment by a legless
  animal dragging its body across a surface.

Burrows, tracks, and trails are examples of
biogenic sedimentary structures (structures made
in an unconsolidated substrate) borings are
examples of bioerosion structures. Trace fossils
are useful in determining the environmental
conditions that prevailed when the traces were
made. They are sometimes useful in age
determinations of sedimentary rocks such as
strata of Cambrian age (590 to 500 million years
old) which contain few body fossils. The term
ichnology was first introduced by the Rev.
William Buckland of Oxford in about 1830.
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Trace Fossil Classification
Trace fossils may be classified according to
their physical characteristics or more usefully
according to the behavioural patterns of the
animal that produced them. There are seven such
behavioural groups (Figure 2)

• Repichnia crawling traces
• Cubichnia resting traces
• Fugichnia escape traces
• Domichnia dwelling traces
• Fodinichnia feeding traces
• Agrichnia framing traces
• Pascichnia grazing traces

FIGURE 2. Classification of trace fossils based
on behavioural patterns.
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FIGURE 3. The behavioural classification of trace
fossils, showing the major categories, and some
typical examples of each. Illustrated
ichnogenera 1. Cruziana 2. Anomoepus 3.
Cosmorhaphe 4. Paleodicyton 5. Phycosiphon
6. Zoophycos 7. Thalassinoides 8.
Ophiomorpha 9. Diplocraterion 10.
Gastrochaenolites 11. Asteriacites 12.
Rusophycus.
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Ichnofacies and environmental usefulness of trace
fossils
One useful aspect of trace fossils is that it has
been discovered that certain assemblage types
characteristic of particular water depths and
environments have occurred through geological
time. For example, deep water abyssal traces
from Cambrian rocks are similar to those produced
today. Ichnologists who study such traces have
identified nine ichnofacies which combine
features of water depth with that of sediment
type and setting. Figure 4 shows the position of
these ichnofacies in a cross section from
terrestrial environments to deep water
environments. Illustrations of examples from some
of these ichnofacies are given in Figure 5.
Scoyenia ichnofacies - low diversity assemblage
in lacustrine environments that may contain
vertebrate trackways some ichnogenera
illustrated in Figure 3 1. Kouphichnium
(kingcrab trace) 2. Isopodichnus. Trypanites
ichnofacies - borings in limestone 3. Polydora
(annelid worm borings) 4. Entobia (clionid
sponge) 5. Echinoid borings 6. Algal borings
and Pholas - see practical). Glossifungites
ichnofacies - typically found on hardgrounds 7.
Pholadid borings 8. Diplocraterion 9. crab
burrow. Skolithos ichnofacies - found generally
in intertidal areas where sediment is often
replaced 10. Skolithos 11. Thalassinoides
12.Diplocraterion 13. Ophiomorpha 14.
Arenicolites. Cruziana ichnofacies - rich
assemblage of crawling and burrowing traces.
Below normal wave base, but not storm base 15.
Phycodes 16. Rhizocorallium 17. Teichichnus
18. Diplichnites (trilobite tracks) 19. Cruziana
20. Rusophycus (trilobite resting trace) 21.
Asteriacites (starfish resting trace). Zoophycos
ichnofacies - range of water depths from shallow
to deep water 22. Zoophycos 23.
Lorenzinia. Nereites ichnofacies - generally in
deep water, in muds and turbidites (24.
Paleodictyon 25. Taphrhelminthopis 26.
Helminthoida 27. Spirorhaphe 28.
Cosmorhaphe. Psilonichnus ichnofacies - found
in supratidal marshes Psilonichnus rootlets
vertebrate tracks. Teredolites ichnofacies -
borings in wood often made by the ship worm
Teredo Teredolites.
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FIGURE 5. Characteristic trace fossils found in
some ichnofacies. See handbook for explanation.
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1. Scoyenia ichnofacies (lacustrine environments)
Scoyenia is a horizontal to vertically oriented,
simple, straight to slightly curved burrow made
by an arthropod (possibly a larval beetle) and is
typically associated with nonmarine environments,
originally formed in moist soils.
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Kouphichnium, walking trace of a kingcrab from
the Upper Jurassic Solnhofen Limestone of Bavaria
1. Scoyenia ichnofacies (lacustrine environments)
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FIGURE 5. Characteristic trace fossils found in
some ichnofacies. See handbook for explanation.
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2. Trypanites ichnofacies (borings in limestone
rocky coast)

• Borings made in wall of Ordovician coral by algae
  or sponge

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2. Trypanites ichnofacies (borings in limestone
rocky coast)

• Borings in chalk made by Recent piddock bivalve,
  Phloas (remember bivalve practical)

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FIGURE 5. Characteristic trace fossils found in
some ichnofacies. See handbook for explanation.
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Vertical burrows (pipes),Skolithus, from the
Grampians of Australia
4. Skolithus ichnofacies (sandy shore 0-10 m
depth, high energy, intertidal areas where
sediment is replaced)
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U-shaped burrows of Diplocraterion from the
Parachilna Formation at the base of the
Cambrian, Ediacara, South Australia
4. Skolithus ichnofacies (sandy shore 0-10 m
depth, high energy, intertidal areas where
sediment is replaced)
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4. Skolithus ichnofacies (sandy shore 0-10 m
depth, high energy, intertidal areas where
sediment is replaced)

• Thalassinoides, a complex burrow system, from the
  Miocene of Libya

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FIGURE 5. Characteristic trace fossils found in
some ichnofacies. See handbook for explanation.
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Cruziana, an arthropod crawling trace from the
Upper Cambrian of Portmadoc, Gwynedd
5. Cruziana ichnofacies (sublittoral zone,
offshore and inner shelf, below normal wave base,
but above storm wave base, 10-100 m depth, also
lagooons)
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5. Cruziana ichnofacies (sublittoral zone,
offshore and inner shelf, below normal wave base,
but above storm wave base, 10-100 m depth, also
lagooons)

• Cruziana, an arthropod crawling trace from the
  Lower Carboniferous of Co. Mayo, Ireland

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5. Cruziana ichnofacies (sublittoral zone,
offshore and inner shelf, below normal wave base,
but above storm wave base, 10-100 m depth, also
lagooons)

• Rusophycos, a trilobite resting trace from the
  Lower Carboniferous of Co. Mayo, Ireland

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5. Cruziana ichnofacies (sublittoral zone,
offshore and inner shelf, below normal wave base,
but above storm wave base, 10-100 m depth, also
lagooons)

• Asteriacites, a starfish trace from the Lower
  Carboniferous of Co. Mayo, Ireland