USGS-GD-Scientific Capabilities - MICROFOSSILS CALCAREOUS NANNOFOSSILS Technique

MICROFOSSILS

CALCAREOUS
NANNOFOSSILS

Technique

 

Calcareous nannofossils are fossil remains of golden-brown, single-celled algae that live in the oceans. Because they are plants, they require sunlight, so they float near the surface of the water. There are billions of them living in the oceans today, and they are eaten by anything that is bigger than they are. They are one of the primary organisms at the base of the food chain.

These algae make tiny calcite platelets inside their cells, and these platelets (the calcareous nannofossils or nannos for short) move to the surface of the cell. The platelets fall off the cell and slowly drift down to the bottom of the ocean. These platelets are replaced by new ones that constantly are forming within each cell. As these platelets land on the bottom of the ocean, they are slowly covered up with remains of other plants and animals and bits of mud and sand that have washed out with the rivers of the world. At this point they are part of a mud or marl or sandy clay. Eventually, there are many sediments on the ocean bottom, and their weight is enough so that the lowest sediments are squeezed enough to become rocks. Chalks are composed almost entirely of nannofossils. Nannofossils also occur in other sedimentary lithologies The calcite platelets are preserved in the rocks and are the fossils that paleontologists study.

Calcareous nannofossils have been living in the world's oceans for at least 200 million years (from the Triassic Period), and they have evolved and changed constantly over time.

Applicaton to Earth Science Research

Biostratigraphy - Calcareous nannofossils are the most useful age indicator for marine sediments from the Jurassic (205 million years) to the Recent because of their rapid rate of evolution and wide geographic distribution. The first appearance datums (FAD's) and last appearance datums (LAD's) for calareous nannofossil species usually occur at the same horizon globally and often can date sediments to accuracies of one million years or less. Accurate dating of sedimentary deposits has many proctical applications. For example, calcareos nannofossils have been used succuesfully to help map both the surface and subsurface geographic extent of lithologic units, particulary in regions with complex facies patterns like New Jersey and Alabama. They also are used in regional geologic studies to correlate time-equivalent but lithologically distinct deposits form state to state and region to region.

Paleoceanography, Paleobiogeography, and Paleoecology - Calcareous nannofossils can be used to help determine the temperature and current patterns of ancient oceans.

Forensic, Art, and History Studies - Calcareous nannofossils have been used in forensic studies. For example, clay scraped from the shoes of a murder suspect in England contained calcareous nannofossil species that were unique enough to lead the police to the scene of the crime. Calcareous nannofossils have been used to determine the origin of building stones for Medieval churches in Denmark and to check authenticity of paintings. In Norway, which has no native chalk, calcareous nannofossils were used to determine the origin of white chalk that was used to prepare the surfaces of Medieval wooden sculptures and panels before painting. The pattern and changes through time of the chalk trading routes probably can be used to interpret general trading patterns in northern Europe at the same time.

Additional Information

Current USGS Projects using Calcareous Nannofossils:

Southern Region Geology Project

Both Mesozoic and Cenozoic calcareous nannofossils are an important part of the south Carolina Coastal Plain Study that is within this project. During the projected five-year extent of this project, calcareous nannofossils will be used as the primary tool to determine the age of marine sediments that are found both at surface outcrops and in numerous coreholes in South Carolina and eastern Georgia. In addition to using previously collected sediments, this project is actively gathering new material by means of (1) coreholes, (2) auger holes, and (3) outcrop sediments. The calcareous nannofossil data, in conjunction withother fossil data and lithologic and geophysical data, will be used to establish a stratigraphic framework for the study area. This framework will form the basis for a widely applicable, comprehensive digital database that encompasses the principal geologic and geohydrologic characteristics of the surface and subsurface Cretaceous an Tertiary strata in South Carolina.

Links

Introduction to the Prymnesiophtya (Coccolithophorids and other Haptophytes) (Museum of Paleontology, University of California at Berkeley)

 


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URL http://geology.cr.usgs.gov/capabilities/paleoanal/microfos/nanno/tech.html