Thermal Effect Evaluation of Basic Sill on Rhythmite of Taciba Formation (Permian), South of Brazil, Using RGB Measurements on Non-Opaque Phytoclasts
The thermal effects on organic matter are the focus of many studies due its importance to the hydrocarbon industry. Through the years many methods to measure these effects such as; vitrinite reflectance (VR), Raman, Rock-eval pyrolysis, Termal Alteration Index (TAI) and Spore Color Index (SCI), have been developed and applied. However, these classical indices are often expensive, time consuming and require equipment not often available to many palynological studies. The current wide access to inexpensive digital color cameras has provided opportunities to develop new methods of thermal effect measurements, such as the Palynomorph Darkness Index (PDI). The PDI is based on grey scales produced by the combination of Red, Green and Blue (RGB) intensities. Despite the effectiveness of the PDI, the palynomorph content in some sequences are scarce, non-continuous or not easy to identify. It is common sense that the organic matter color responds to the temperature increase, then the PDI principle can be apply to other kerogens components e.g. non-opaque phytoclast (NOP). Here, we report on the evaluation of the thermal effect sill emplacement on rhythmites of the Taciba Formation (Lower Permian), south of Brazil, using RGB measurements on NOP. The outcrop, José Guelbcke, located in the city of Itaiópolis, Santa Catarina, Brazil, comprises a 5m sill above a 4.5m fossiliferous rhythmite (subdivided in 9 levels). A sample of each level has been analyzed using OLYMPUS IX83 equipped with the digital camera Olympus DP73 with 17 mpixel resolution. The luminosity was calibrated and pre-set. The kerogen compound, non-opaque phytoclast were chosen due there abundance. Fifteen NOP randomly chosen in each level have been measured. The values obtained were the mode of RGB intensities in all pixels on the selected NOP. The result were converted to a greyscale value and then applied in the PDI formula to obtain the NOP darkness index (NOPDI). Scale ranges from white to black are used. Three distinct groups have been observed in the sequence, from levels 0.5 to 2.0m the NOPDI vary from 37,86% to 45.57%; from levels 2.5 to 4.0m the NOPDI range from 58.28% to 61.27%; and in the upper level (contact with the basic sill) was 70.39%. The NOPDI results allows us not only to assign that the thermal effectiveness of the sill penetrated only 2.5 m beneath the intrusion, but also that the first group of values represent the pre-intrusion conditions, as for example, background diagenesis.
AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018