High-temperature wood silicification: constraints from fluid and carbonaceous inclusions in quartz from Qitai, NW China

Silicified wood serves as a crucial geological archive, recording significant information about palaeoenvironment, palaeoecology, palaeontology and diagenetic conditions. However, temperature and pressure conditions of silicification remain poorly constrained. In this study, we analysed primary fluid and carbonaceous material inclusions in quartz from silicified wood in the Qitai Silicified Forest, Xinjiang. Microthermometry and Raman spectroscopic studies reveal the methane-bearing silicification fluids, with salinities of 12.05-14.87 wt% NaCl equiv., densities ranging from 0.94 to 0.96 g/cm³, homogenization temperatures in the range of 238-257 °C, and provide the converting temperatures of 285 ± 30 °C for carbonaceous inclusions. Silicification temperatures are constrained to 238-315 °C, supported by successive silica precipitation. The thermal model analysis of inclusion isochores and thermobaric gradients, burial history of the Junggar Basin, and the presence of volcanic tuff hosting silicified wood limit the silicification pressure in the range between 0.1 MPa (surface conditions) and ~ 50 MPa. These findings provide the first quantitative P-T constraints on wood fossilization, revisit its thermal limits, and facilitate the study of wood fossil genesis in volcanic environments globally. Quantifying the P-T thresholds of wood silicification not only renews models of plant fossil preservation but also provides insights into how forest fossils reflect extreme palaeoenvironments.