Author Description

Organic matter (OM) quantity, quality, and thermal maturity are key parameters in both conventional and unconventional petroleum systems. Understanding the stratigraphic distribution of OM content and type in black shale successions and its transformation during thermal maturation is of great significance in source rock evaluation and unconventional shale oil/gas exploration and development. In this study, organic petrography, scanning electron microscopy (SEM), micro-Fourier transform infrared spectroscopy, portable x-ray fluorescence spectroscopy, and inductively coupled plasma-mass spectrometry techniques were used to study the heterogeneity of OM in the Upper Devonian New Albany Shale (NAS) in the Illinois Basin. Specifically, this research aims to (1) document the distribution of total organic carbon content (TOC) content and maceral types in the sequence stratigraphic context of the NAS; (2) study the association of uranium (U) with organic matter and maceral types; (3) document the transformation of oil-prone macerals and characterize the evolution of the chemical structure of macerals and solid bitumen (SB) during thermal maturation across a maturation gradient from vitrinite reflectance (Ro) 0.55% to 1.42%; and (4) examine the control of thermal maturity and maceral type on the development of secondary organic pores using correlative microscopy (SEM and reflected-light microscopy). The results show that within a sequence stratigraphic context, TOC content increases in transgressive systems tracts, reaches a maximum just below maximum flooding surfaces, and shows relatively low values in highstand systems tracts. Bottom-water redox conditions are one of the controlling factors for OM enrichment in the NAS. U in the NAS is mainly associated with sedimentary OM. Amorphous organic matter (AOM) derived from degraded phytoplankton, zooplankton, and bacterial biomass is the primary host of U in the NAS. Alginite and terrestrial OM have negligible contributions to