الرحيم الرحمن الله بسم

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.

The Pleistocene Mammoth of Sibera

Complete unaltered remains

Unaltered hard parts

Preservation with alteration

• 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 (non-volatile) 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

• 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

Replacement

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

External mould

Internal mould

External mould

Internal mould

Clam Fossil clam

Fossil snailSnail

Shell is dissolved

Shell is dissolved

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!• Moulds• Replacement• Casts• Recrystalization• Permineralization• Ichnoossil (trace fossil)

Choose the correct answerChoose 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 preservationWrite the modes of preservation

CompleteComplete

• Examples of preservation without alterations…..… and ……….

• Examples of preservation with alterations…..… and ……….

Report subjectsReport subjects

• Fossilization• Porifera• Coelenterata• Bivalvia• Gastropoda• Cephalopoda• Echinodermata• Brachiopoda• Bryozoa• Trilobita