299-8 Relationships between vitrinite reflectance and Rock-Eval Pyrolysis Tmax temperatures in Pennsylvanian rocks of the central and northern Appalachian basin

Session: Geochemical Studies of Sediments (Posters)

Presenting Author:

Authors:

Abstract:

The thermal maturity of sedimentary basins can greatly impact authigenic mineral formation, fluid

migration, coal rank, and hydrocarbon production. Two commonly applied thermal maturation

indicators in sedimentary basins include vitrinite reflectance (VR) and Rock-Eval pyrolysis (REP).

VR is a measure of the percentage (%Ro) of incident light reflected from vitrinite observed in thin

section, while REP is determined through the progressive heating of rock samples during which

hydrocarbons and other organic materials are volatilized. In VR determinations, samples with higher

maturity generally display higher %Ro values. For REP analyses, samples that are more thermally

mature generally require higher temperatures to produce the maximum release of volatiles (Tmax)

during pyrolysis. While VR is commonly viewed as a standard metric for thermal maturity of

organic-rich deposits, REP Tmax temperatures are commonly employed due to the relative ease in

sample preparation and evaluation. The primary goal of this investigation was to evaluate the

relationship between VR %Ro and REP Tmax temperatures. To this end, we sampled organic-rich

mudrock (n=30) from Pennsylvanian-age rocks in the central (eastern Kentucky and southern West

Virginia) and northern (eastern Ohio, Pennsylvania, western Maryland, eastern West Virginia) parts

of the Appalachian Basin from locations in close proximity to published coal VR sample localities

(Ruppert et al., 2014). Sample REP Tmax temperatures ranged from, 420 – 608 °C for VR %Ro

values of 0.55 – 5.65, respectively. The sample suite displayed a close correlation between sample

Tmax and VR values (r²=0.82) that was improved (r²=0.92) with the omission of samples with TOC

values of <0.75% and %Ro values >3.5. Collectively, study results indicate that pyrolysis Tmax

temperatures in carbonaceous mudrocks can be confidently used as a proxy for coal VR %Ro in all

but the most thermally mature areas (e.g. the Anthracite Region of northeastern Pennsylvania) of the

basin.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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