An organic geochemical study of bitumens and their potential source rocks from the South Pennine Orefield, Central England

Abstract

Bitumens associated with PbZn mineralisation hosted by upper Dinantian limestones in the South Pennine Orefield (Derbyshire, Central England) were characterised in terms of maturity as well as source/correlation parameters, and compared with hydrocarbons from the East Midlands oilfield and bitumens from the Cheshire Basin. Potential source rocks from within the Dinantian sequence and from the lower Namurian mudstones of adjacent Carboniferous sedimentary basins were characterised in a similar fashion. The bitumens from both Derbyshire and Cheshire show a range of effects due to biodegradation and water washing, from partial to complete removal of n-alkanes, isoprenoids and polyaromatic hydrocarbons. The bitumen/oil suite (Derbyshire bitumens, Cheshire bitumens and East Midlands oils) show mature biological marker distributions. Whilst the Derbyshire bitumens and East Midlands oils generally correlate well with each other, bitumens from Cheshire show distinct differences. On the grounds of maturity and source/correlation biological marker characteristics, it is possible to suggest likely source rocks for the Derbyshire bitumens and East Midlands oils. Using a “multiparameter approach”, lower Namurian mudstones from the Widmerpool Gulf, along with those from the Gainsborough and Goyt Troughs, are not regarded as source rocks. The lower Namurian mudstones from the Edale Gulf correlated with the East Midlands oils and Derbyshire bitumens on the basis of a restricted number of biological marker compound classes. Bulk and molecular maturity parameters also indicate that these particular formations could have generated hydrocarbons. More local contributions to the Derbyshire bitumens may have been made by some of the organic-rich mudstones within the Dinantian succession.