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‫بسم هللا الرحمن الرحيم‬
Modes of preservation
Modes of preservation
• Preservation without alteration
• Preservation with alteration
• Trace fossils
Preservation without alteration
• In rare cases, soft and hard parts may preserve
due to freezing of organisms, such as the
mammoths of Siberia or due to entrapment of
organisms in resin (amber) and oil seeps such as
insects.
• Also hard parts consisting of calcite, silica and
calcium phosphate, as in molluscs, brachiopods,
bryozoans…may preserve without alteration,
especially of Quaternary and Tertiary periods.
Complete unaltered remains
Unaltered hard parts
Preservation with alteration
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Carbonization
Permineralization
Recrystallization
Replacement
Molds and casts
Trace fossils
Carbonization
• The process of carbon enrichment of organic-rich
remains through their burial and heating.
• Organic remains, when buried to relatively shallow
depths, are lightly heated.
• During this low-grade cooking, the volatile
elements such as oxygen, hydrogen, and nitrogen
are released as gasses, while carbon (nonvolatile) is left behind.
• As a result, the remains are increasingly enriched
in carbon.
• Carbon films and coal are the typical product of
this process.
Carbonization
This carbon-film fossil of a fern is more than 300 million years old.
Permineralization
• Deposition of mineral material, most commonly
of calcium carbonate, silica, pyrite, dolomite from
underground solutions in pore spaces of buried
remains.
• The new materials increase hardness and
weight of skeletons and help them to
fossilization.
Recrystallization
• Conversion of less stable compounds into a more
stable form, without change in chemical
composition of the skeleton (change in crystal
form).
• Ex. Aragonite to calcite in scleractinian corals and
gastropods.
• Fine crystals changed to coarse one.
Recrystallization
Increased size of crystals
Replacement
• Complete replacement of skeletons (molecule by
molecule) by new mineral material such as calcite,
dolomite, silica, and iron compounds.
• Ex. Petrified wood.
Calcification.
Silicification.
Pyritization.
Dolomitization
Silicification
Pyritization
Moulds
• External mould is the impression that the buried
object made in the surrounding sediment
(impression of shell exterior surface)
• Internal mould forms when the buried object is
hollow, and infilled with sediments (impression of
shell interior surface)
Internal
mould
External
mould
Moulds
Fossil clam
Clam
Internal mould
Shell is dissolved
External mould
Snail
Fossil snail
Shell is dissolved
External mould
Internal mould
Casts
• Casts are formed when the void within an exterior
mould is filled in by siliciclastic sediment or minerals
precipitated from ground water.
•The product of this infilling is a cast) take the
internal and external morphology of the original
remains.
Cast of Tree Trunk
Trace Fossils
Preserved structures in sedimentary rocks express the
vital activity of organisms without presence of body
fossil. There are many types of trace fossils:• Tracks and trails: Footprints of animals and birds,
indicating the movements by invertebrates.
• Burrows and borings: Excavations made by worms
and other animals such as clams, crabs, shrimp, or fish
as they tunnel into sediments.
• Coprolites: Fossilized animal excrement, may give
evidence of diet, animal size, and habitat.
•
Give the scientific term
• The process of carbon enrichment of organic-rich remains
through their burial and heating.
• Deposition of mineral material, from underground solutions
in pore spaces of buried remains.
• Conversion of less stable compounds into a more stable
form, without change in chemical composition of the
skeleton.
• The impression that the buried object made in the
surrounding sediment.
• Preserved structures in sedimentary rocks express the vital
activity of organisms.
• Formed when the buried object is hollow, and infilled with
sediments.
Define!
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Moulds
Replacement
Casts
Recrystalization
Permineralization
Ichnoossil (trace fossil)
Choose the correct answer
• The process of carbon enrichment of organic-rich
remains through their burial and heating.
a) Carbonization
b) Replacement
c) Permineralization
• Deposition of mineral material, from underground
solutions in pore spaces of buried remains.
a) Carbonization
b) Replacement c) Permineralization
• Conversion of less stable compounds into a more stable
form, without change in chemical composition of the
skeleton.
a) Carbonization
b) Replacement
c) Recrystalization
• Preserved structures in sedimentary rocks express the
vital activity of organisms.
a) Trace fossils
•
b) Replacement
c) moulds
Write the modes of preservation
Complete
• Examples of preservation without alterations…..…
and ……….
• Examples of preservation with alterations…..… and
……….
Report subjects
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Fossilization
Porifera
Coelenterata
Bivalvia
Gastropoda
Cephalopoda
Echinodermata
Brachiopoda
Bryozoa
Trilobita