Application of transmitted light techniques for evaluation of thermal maturity

Status Start Date End Date Locations
completed Jun 1, 2014 Feb 29, 2016 All Counties
Director: Maria Mastalerz
Other Researchers: Agnieszka Drobniak
Funding: Indiana University - Indiana Geological & Water Survey
Issue: Even though organic petrography techniques are dominated by reflected light microscopy, and measurements of vitrinite reflectance have been a standard technique to evaluate thermal degree of maturity of organic matter for some years observations of organic matter in transmitted light remain an effective way to also evaluate maturation changes. The thermal alteration index (TAI), a parameter based on transmitted light observations, uses color changes in organic matter to evaluate sediment maturity.
Objective: Project analyzes changes in color of structureless amorphous organic matter and palynomorphs in transmitted light through a range of maturity stages.
Approach: The changes were observed from immature (Ro <0.30%) to post mature samples (Ro >4.00%) based on shales from various ages (Silurian to Tertiary) and geographic locations. Thermal Alteration Index (TAI) assessed based on the color of structureless organic matter and Spore Color Index (SCI) is compared to vitrinite reflectance values obtained on more than 200 samples. A subset of 180 samples was used to establish a relationship between Tmax and vitrinite reflectance.
Products: Mastalerz, M., Hampton, L. Drobniak, A., Transformation of structureless organic matter with maturation: Thermal alteration index (TAI) revisited: International Journal of Coal Geology (submitted). Mastalerz, M., Hampton, L. Drobniak, A., Application of transmitted light technique for evaluation of thermal maturity: Color changes in structureless organic matter and palynomorphs: Indiana Geological Survey Occasional Paper 73. Mastalerz, M., Hampton, L. and Drobniak, A., Thermal maturation index (TAI), vitrinite reflectance, and Tmax through maturation – abstract for the 32nd Annual Meeting of the Society for Organic Petrology, Yogyakarta, Indonesia, September 20-27, 2015.
Benefits: The primary purpose of this project is to document color changes of structureless amorphous organic matter as well as color of palynomorphs with increasing maturation in shale samples of various ages from Silurian to Tertiary coming from various geographic locations in an effort to build more universally applicable TAI and SCI scales. Although both TAI and SCI are commonly used in industry to evaluate maturity, no comprehensive sets of photomicrographs of structureless organic matter and palynomorphs are available in the literature for use as a reference or for instructional purposes. Photomicrographs taken during this project can serve as color reference for individuals who use these techniques