Calcareous Nannofossils
Calcareous nannofossils are minute calcite plates from marine algae that provide extremely high-resolution dating of Mesozoic and Cenozoic sediments.
Definition
Calcareous nannofossils are microscopic calcite structures, chiefly coccoliths, secreted by single-celled marine algae and preserved abundantly in fine-grained marine carbonates.
Scope
This topic covers coccoliths and other calcareous nannofossils produced by haptophyte algae, their structure observed by light and electron microscopy, their evolution since the Triassic, and their use in fine-scale biostratigraphy and paleoceanography.
Core questions
- What organisms produce calcareous nannofossils?
- Why do nannofossils give such high biostratigraphic resolution?
- How are nannofossils studied and identified?
- How do they record ocean productivity and chemistry?
Key concepts
- Coccoliths and coccospheres
- Haptophyte algae
- Nannofossil datums and zones
- Chalk and carbonate accumulation
Key theories
- Nannofossil biostratigraphic zonation
- Rapid evolution and global distribution of coccolithophores yield closely spaced datums that subdivide Mesozoic and Cenozoic time finely.
- Coccolithophores as rock builders
- Accumulated coccoliths form major deposits such as chalk and contribute to the marine carbon cycle and carbonate record.
Clinical relevance
Calcareous nannofossils provide some of the finest available time resolution for marine strata in exploration and academic stratigraphy, and their abundance archives ocean productivity and carbonate chemistry through time.
History
Coccoliths were first seen in chalk in the mid-nineteenth century, but their biostratigraphic potential was realized only with electron microscopy and deep-sea drilling in the twentieth century, after which they became key zonal fossils.
Debates
- Drivers of nannoplankton turnover
- The relative roles of climate, ocean chemistry, and mass extinctions in shaping nannoplankton diversity through time remain studied.
Key figures
- Paul R. Bown
- Hans R. Thierstein
- Katharina von Salis
Related topics
Seminal works
- bown1998
- armstrong2005
Frequently asked questions
- What are coccoliths?
- Coccoliths are tiny calcite plates produced by single-celled marine algae called coccolithophores; vast numbers of them form chalk deposits.
- Why are nannofossils so useful for dating?
- They evolved quickly, spread across the oceans, and occur in enormous numbers, so their appearances and extinctions mark very narrow time intervals.