CHARACTERIZATION OF AMORPHOUS ORGANIC MATTER (AOM) IN ORGANIC-RICH SHALES OF THE CARBONIFEROUS PENNINE BASIN (UNITED KINGDOM) (Invited Presentation)

Kerogen in Serpukhovian (late Mississippian) mudstones in the Pennine Basin (northern England) consists of 90–95% amorphous organic matter (AOM). These high abundances reflect that AOM, despite being poorly constrained as it lacks a distinct morphology and is of unknown origin, determines the quality and influences the quantity of hydrocarbons contained in the mudstones. 

In Mississippian times, the Pennine Basin consisted of a mosaic of inter-linked basins formed due to crustal extension north of the Hercynic orogenic zone. The data presented here was collected from cores from two basins: the Widmerpool Gulf and the Edale Gulf. A new scheme with a focus on AOM was developed to characterize palynofacies using transmitted light microscopy. This revealed a covariance of terrestrially sourced material and homogeneous AOM. Transmitted electron microscopy showed that the texture of the amorphous particles consists mostly of mineral imprints suggesting a diagenetic overprint on the original texture. This observation has potentially far-reaching consequences as the reactive surface of these organic particles is much larger than originally expected.

To complement the palynological dataset, a suite of geochemical techniques including stable isotope analysis shows dominance of heterogeneous AOM in more marine parts of the stratigraphic column. Rock Eval pyrolysis confirms the highly variable nature of the Mississippian mudstones in the Pennine Basin, suggesting a high resolution approach will be necessary to correctly assess the prospectivity of this stratigraphic unit.

From the kerogen fraction we isolated AOM and analysed using Rock Eval pyrolysis and pyrolysis gas chromatography. This showed a type II origin for most of the AOM with some horizons prospective for gas and condensates. These results again emphasizes the need for high resolution palynological and geochemical characterization of the British Mississippian mudrocks.