Differences in thermal decomposition and crystallinity of dark organic laminae and light mineral laminae in same stromatolite

Abstract

Stromatolite was a typical representative of microbial carbonate rocks, and also a unique microbial sedimentary structure in carbonate rocks. Previous studies on the characteristics of dark organic laminae and light mineral laminae in same stromatolite have carried out a lot of work, but there was less research in thermal decomposition and crystallinity. Here, X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were used to determine the mineral composition and organic components of stromatolite and micrite. In addition, TG, DTG and were used to analyze their thermochemical characteristics and the non-isothermal decomposition of stromatolite and micrite at multi-heating rates of 5, 10, 20 and 30 °C min−1 in nitrogen atmospheres. Moreover, kinetic model function, kinetic parameters of apparent activation energy (E), and pre-exponential factor (A) were calculated by Popescu, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS). The results showed that the mineral composition of two laminae structures was calcite, but there were organic matter and organic functional groups in the dark laminae. In addition, the results of thermal analysis showed that the crystallinity and thermal stability were significantly different, that was, crystallinity and thermal stability of dark laminae were significantly higher than that of light laminae. Moreover, the kinetic calculation results showed that the activation energy of dark laminae was also higher. These results provided an important reference for analyzing the thermochemical characteristics of stromatolite, especially the differences in dark organic laminae and light mineral laminae of the stromatolite.