Nannopalaeontology is the study of minute calcareous fossils, extracted from fine grained rocks such as muds, clays and silts. These fossils are much smaller than the fossils studied for micropalaeontoloy or palynology. Nannofossils include; spicules, juvenile foraminifera and calcispheres (calcareous dinoflagellates) and the plate-like remains of unicellular algae (coccoliths and nannoliths).
The individual fossils are minute in size, typically ranging from 2 to 25µm. Their small size adds to their utility. Mechanical damage during drilling is unlikely, leading to good preservation and vast number of nannofossils can be found in relatively small amounts of sediment, making biostratigraphic analysis possible when material is in short supply.
By far the most dominant nannofossil group, are the remains of unicellular haptophyte algae (phytoplankton or nannoplankton) known as coccoliths. These are generally disc-like in form and would have comprised the exoskeleton of an individual coccolithophorid.
There are also a large group of various-shaped nannofossils known as nannoliths; their biological affinity is not clear based on the lack of modern analogues. The nannolith group includes the ‘discoasters’ (genus Discoaster), a very important group, used extensively in biostratigraphy, especially in the Neogene Period (~2.5 to 23Ma).
Calcareous nannofossils can be found extensively across all marine environments, from coast to open ocean. The earliest known calcareous nannofossils are of Late Triassic age and range through the geological record to present day seas, making them indispensable as a biostratigraphic tool.
Their rapid rate of evolutionary change and widespread global distribution allows a high resolution biostratigraphic breakdown, which can define intervals as small as 0.1Ma in the Pleistocene, allowing development of robust global nannofossil zonation schemes.
The application of nannopalaeontology at wellsite has, time and time again, proven itself invaluable. Sample preparation is quick, simple and low cost allowing real time, cost efficient, biostratigraphic coverage whist drilling. Whether used to biosteer horizontal wells in complex geology, locating and defining faults, picking casing points and TD depths or monitoring well sections to provide comprehensive age data for immediate use, nannofossils cannot be overlooked.
Nannofossils also have palaeoceanographic, paleoenvironmental and palaeoecological applications; being used to help determine temperature and current patterns in prehistoric oceans.