Key Facts
● The study of marine planktonic and benthonic microfossils.
● Palaeozoic to Holocene
● Very abundant in marine deposits and certain non-marine sediments.
● Versatile tool to carefully assess paleoenvironments and palaeobathymetry.
What is Micropalaeontology?
Micropalaeontology is a discipline of palaeontology mainly concerned with fossils (generally >63 microns) that require microscopes for study including foraminifera, ostracoda, radiolaria and diatoms.
Associated identification of key minerals, fragments of small invertebrates, evidence for bioturbation and drilling artefacts (i.e. mud additive) are also important during analysis. Microfossils have great utility in accurately interpreting the stratigraphic age and environment of deposition.
Diatoms
Are a major group of unicellular algae, producing silica skeletons, and living as solitary organisms or as part of colonies. They are photosynthetic, generating around 20% of the oxygen produced on our plant annually. They take a variety of shapes, including; zig-zags, ribbons, fans or stars. Fossil evidence indicates this group originated in the Early Jurassic, and inhabit both marine and non-marine environments. They have undergone rapid evolution making them useful biostratigraphically.
Foraminifera
Foraminifera inhabit most marine-marginal marine environments and are often very abundant, accounting for over 90% of deep sea biomass. They are single-celled protists with an external shell/test composed of calcium carbonate, aragonite or cemented agglutinated grains. They are a principal microfossil group used to age-date and correlate marine sedimentary rocks of Late Palaeozoic, Mesozoic and Cenozoic age. Moreover, planktonic foraminifera which are geographically widespread and have rapidly evolving lineages and some smaller benthonic foraminifera are widely used for regional stratigraphy.
Ostracods
Ostracods are a class of Crustacea, sometimes informally known as “seed shrimp”. These tiny crustaceans have bivalve-like shells protecting their inner bodies; these shells are chitinous or calcareous, and their preserved remains date back to the early Ordovician. In marine environments, they inhabit the upper layers of the ocean floor sediments. They can also be found in freshwater environments, as well as in humid forest soils in the terrestrial realm. They can be used for biostratigraphic delineation and are also very useful for palaeoenvironmental interpretation, especially when integrated with other groups.
Radiolaria
Radiolaria single-celled microplankton that produce intricate mineral skeletons usually composed of silica. They are found throughout the ocean systems of the world, and their skeletal remains rain down onto the ocean bed as a siliceous ooze. This group has been present since the Cambrian, and their rapid evolution throughout geological time makes them an excellent biostratigraphic tool.
Cambrian to Holocene Biostratigraphic Tool
Micropalaeontology has proven to be a reliable biostratigraphic tool for rocks dating ranging from Cambrian to Holocene (modern day).
Paleoenvironments and Paleobathymetry
Microfossils are highly sensitive to environmental changes and can be present from the terrestrial (ostracods and diatoms) to the deep marine (foraminifera, radiolaria, ostracods, diatoms). Therefore, relative changes in a microfossil assemblage composition throughout a section can be a versatile tool to interpret the environment of deposition and distance from palaeo-shoreline.
Principally this is achieved by investigating:
- The causal association between microfaunal distribution (abundance and diversity) and sea levels.
- Particular benthonic foraminifera genera and species proliferate in specific environments which can be characterised based on their Morphogroup characteristics.
- Distribution of planktonic microfossils (foraminifera, radiolaria, diatoms) in the pelagic regime reflects distance from shore and the degree of open marine connectivity which can be distinguished into key zones.
