Thermal maturity map of Devonian shale in the Illinois, Michigan, and Appalachian basins of North America

Abstract

Source Rock Maturity Immature (%R o values < 0.6) Oil window (%R o values 0.6 to 1.3) Gas window (%R o values 1.3 to 2.0) Overmature (%R o values > 2.0) Outline of basin Outline of maximum extent of Devonian shale-Dashed where concealed Sample with %R o value Sample with conodont CAI value Sample with SCI value 0 50 100 150 200 250 miles 0 50 100 150 200 250 300 350 kilometers Michigan basin Illinois basin Appalachian basin Conodont Color Alteration Index (CAI) Liptinite Fluorescence Thermal Alteration Index (TAI) Hydrocarbon Generation / Preservation Events Vitrinite Reflectance in %R o (mean)

Post‐orogenic thermal history and exhumation of the northern Appalachian Basin: Low‐temperature thermochronologic constraints

“…%R o values for individual samples were estimated based on their proximity to %R o isograds or, if samples were within <15 km of a %R o drill core location, values were estimated directly from measured values (Table ). Given that the Devonian shales measured by East et al () and Ryder et al () are stratigraphically below our samples (Figure ), %R o values were interpreted as an absolute maximum bound for potential maximum paleotemperature experienced by our samples.…”

“…Published %R o values (East et al, ; Repetski et al, ; Ryder et al, ) and measured CAI data all indicate increasing maximum paleotemperatures from west to east, ~100°C to >200°C. Our younging AFT age trend is consistent with the pattern shown by maximum paleothermometer values (Figure ).…”

“…The PAZ (~60–120°C, depending on composition) and PRZ (~40–80°C) are marked with dashed lines. Published %Ro values (East et al, ; Ryder et al, ) are shown with dashed, double headed arrows when they are within bounds of figure (i.e. <200°C).…”

“…The percentage of light reflected off vitrinite, an organic substance naturally occurring in rocks, is a proxy for thermal maturity primarily controlled by temperature and time (Sweeny & Burnham, 1990). Published maps of %R o values from Devonian shale drill core and cuttings samples (East, Swezey, Repetski, & Hayba, ; Ryder, Hackley, Trippi, & Alimi, ) were used to estimate %R o values for this study's samples. %R o values for individual samples were estimated based on their proximity to %R o isograds or, if samples were within <15 km of a %R o drill core location, values were estimated directly from measured values (Table ).…”

“…The PAZ (~60-120°C, depending on composition) and PRZ (~40-80°C) are marked with dashed lines. Published %Ro values (East et al, 2012;Ryder et al, 2013)…”