The Foraminiferal Colouration Index McNeil, D.H., Issler, D.R., and Snowdon, L.R., 1996, Colour alteration, thermal maturity, and burial diagenesis in fossil foraminifers. Geological Survey of Canada, Bulletin 499, 34 p. (FCI) is a tool for assessing the thermal alteration of organic matter buried in

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particle ...

. It uses temperature-controlled colour changes in the organic cement of agglutinated foraminifera (

microfossils A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

) to estimate thermal alteration. The method is empirical and based on determination of colour by visual comparison of fossil specimens to the

Geological Society of America The Geological Society of America (GSA) is a nonprofit organization dedicated to the advancement of the geosciences. History The society was founded in Ithaca, New York, in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitch ...

Rock-Color Chart ( Munsell colour system) under a binocular microscope. The FCI values 0 to 10 are indicated below: Agglutinated foraminifera have a long geological history spanning the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...

, and

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

. The FCI has many potential applications especially in the analysis of samples from hydrocarbon exploration wells.McNeil, D.H., Dietrich, J.R., Issler, D.A., Grasby, S.E., Stasiuk, L.D., and Dixon, J., 2010, A new method for recognizing subsurface hydrocarbon seepage and migration using foraminiferal alteration documented from a gas chimney in the Beaufort-Mackenzie Basin. In L. Wood, ed., Shale Tectonics: American Association of Petroleum Geologists, Memoir 93, p. 197-210. Significant colour changes (FCI 2 to 6) occur through a temperature range of ~60 °C to ~110 °C. The FCI is therefore an indicator of temperatures required to initiate petroleum generation (oil window). The onset of oil generation correlates approximately to FCI 5–6.

Raman spectroscopy Raman spectroscopy () (named after Indian physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman s ...

(an analytical tool for fingerprinting molecules) has confirmed that organic cement is present in fossil agglutinated foraminifera.McNeil, D.H., Schulze, H.G., Matys, E., and Bosak, T., 2015, Raman spectroscopic analysis of carbonaceous matter and silica in the test walls of recent and fossil agglutinated foraminifera: American Association of Petroleum Geologists Bulletin , v. 99, p. 1081-1097. Raman spectroscopy and the FCI can be used to estimate thermal maturity and, therefore, assess thermal conditions necessary for hydrocarbon generation. The FCI methodology is similar to the Conodont Alteration Index (CAI), but the colour/temperature relationships differ in that FCI is more sensitive to colour change at lower temperatures.

References

{{Reflist * Sedimentology Fossilization