admin    August 18, 2021    0

Palaeontology in a broad sense is the study of the remains or traces of the activities of once living organisms called fossils which have been stored in rocks through natural processes. Palaeontology can generally be sub-divided into;

  • Micropaleontology, the study of macroscopic fossil such as dinosaurs, fossilized tree stumps etc.
  • Micropaleontology concerned with the study microscopic (micro) fossils. The term is sometime associated to the study of mineral walled microfossils such as foraminifera.
  • Palynology which is the study of organic walled microfossils


Modes of fossil preservation

Fossils are preserved either as unaltered body fossils or altered fragments and traces through one or a combination of the following processes.

  • Desiccation: Rapid drying of organisms that limits decay and preserve the organism in a mummified state.
  • Permineralization: the replacement of internal parts of and organism with precipitated minerals
  • Replacement : Minerals can replace bone, shell, wood, and even soft body parts as they dissolve away due to the action of water and decay
  • Recrystallization: the transforming of mineral parts of organisms from one mineral to a more stable form that allows preservation e.g, Calcite to aragonite.
  • Carbonization: compression of a fossil within lithifying rocks that leaves behind a thin carbon film outline of the organism
  • Formation of moulds and casts: Three-dimensional impressions of organism shapes preserved in rocks (mostly sedimentary).


Microfossils Used in Petroleum Exploration

Three main groups of microfossils have been extensively used in petroleum exploration. They include foraminifera, Calcarous nannofossils and palynomorphs.

Foraminifera:  These are protists that form shells called tests by secreting calcium carbonate or gluing sand and salt grains together. They first occuured in benthonic and evolved later (Mesozoic and Cenozoic) to planktonic forms.

Calcareous Nannofossils: they are extremely small (usually <25µm) organisms made up of calcium carbonate and are mostly produced by marine algae.

Coccolithophorans are known for the production of plantonic golden brown algae nannofossils. The organism produces calcareous plates (coccoliths) as shells which they shed after growth or death. The shells accumulate to form the nannofossils

Palynomorphs: these are organic walled microfossils consisting mainly of plant pollen and spores as well as some marine organisms like dinoflagellates. They are generally very resistant to weathering and transportation, hence are transported over very long distances and are amongst the most abundant fossils.