Paleontology/Introduction/Geological structures of fossiliferrous bearing material

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Before we can find fossils, we need to know if a rock strata can be able to contain fossils. This is because not all rock contain fossils, those from w:Volcanoes and w:divergent tectonic plates (like in Iceland) are less likely to contain fossils because of the way they are formed. A basic understanding of Earths processes can be found here. Smithsonian Institution: Introduction to Earths processes

Multicoloured limestone rock caused by intrusion of other minerals, at São Pedro de Muel beach, Marinha Grande, Portugal

Types of fossil bearing rocks.[edit]

The most likely rock to find fossils would be in (w:Sedimentary rock), and for these there are three types we are concerned with. The first is called Clastic rock which is made up of sand based material like sandstone, shale, conglomerate etc. The second rock are called Biogenic such as the w:Small shelly fossil, as they are formed from the animals themselves, they include coal, limestone etc, and similar secondary rock such as marble which is metamorphasized limestone. The last is Evaporates, phosphate rocks and nodule type rocks, these usually percipitate out of the ground, from evaporated water bodies such as salt lakes and are known as massive or nodular deposits as they are a very concentrated material.

Minerals for fossilization[edit]

Limestone with fossil bivalves

Organic material of all kingdoms of life are usually replaced mainly by phosphates and smaller amounts of other minerals. In this process, fossils that contain hard parts (shell, bone etc) are readily preserved as the salts and phosphates reduce or kill bacterial and other concentrations that destroy skeletal or exoskeletal organic matter. But in soft boddied organisms without a skeletal frame (like jellyfish, worms etc) are preserved in exceptional circumstances. The salts and phosphates can also destroy the softer tissue allong with bacteria.

These deposits are usually formed in low lying areas where sedimentary material can accumulate, and in doing so making the depression shollower. These can encompass water and land bodies, so long as there is a depression where sediment can accumulate and minimal erosion does occurs. Some examples are subterranian caves, trenches, lakes, cratons and the like. (Philips 2003 pp.31-35, McGeary and Plummer (1994) pp.267-283)

Sedimentary rock formation.[edit]

For the main topic see Sedimentary rocks

The build up of sedimentary formations is the results of compaction or w:lithificationof debre from eroded geographical formations, organic precipitates and the compacetion of other material. Sedimentary formations can be composed of w:Igneous rocks, other w:sedimentary rocks, or w:metamorphic rocks, which is an altered state of igneous, sedimentary or other metamorphic rocks, caused by pressure and or heat.

Torridonian sandstone shows strata of arkosic sandstone laid down around 1000 million years ago. By Anne Burgess

All three rock classifications belong to a cycle called the Rock Cycle with no begining and no end, but all rock is continously changed and altered depending unpon the conditions it is currently in. Sediment accumulates (lithifications) to form sedimentary rock strata. As new layers form on top of older layers, the older material is compacted the spaces between the grains is reduced. There can either be with or without cementation. The accumulation causes a rise in ground level , so an increase in the crustal thickness of the local deposit area, which would cause a lowering of the crust into the mantle to form a state of w:isostatic adjustment.

There are four types of sedimentary rock.

Readings[edit]

Distribution of fossil bearing rock strata.[edit]

Microfossils from Antarctic marine sediments. Click on picture for more information.

All continents and some islands like Crete, Greenland, New Zealand bare rock of a sedimentary kind, but not all of these areas have fossil formations within the sedimentation. A list of fossil localities as indicated in the w:List of fossil sites article on wikipedia.

A majority of these rock formations are w:shale, w:sandstone and w:limestone. But many more less common rock formations do occure such as w:conglomerates and w:breccia (McGeary and Plummer).

Reading material[edit]