Hydrocarbon-bearing nodules from Heysham,Lancashire

Nodules enriched in hydrocarbon occur sparingly in a subarkose bed of Namurian (?Kinders-coutian) age near Heysham, Lancashire. The nodules are commonly spheroidal to ellipsoidal (1-9 cm across) and are composed of alternating shells of hydrocarbon-rich and hydrocarbon-poor sandstone. Irregular impregnations and pellets are also formed from hydrocarbon. The hydrocarbon is infusible, insoluble in CCl₄, CS₂ and petroleum naphtha, and is classified as a pyrobitumen. Ash content averages 22.1% and the ash contains major V; subordinate Fe, U, Ca; minor Pb, Ti; traces of Ba, Mn, Zr, Ga, Y, Sr, Ni and Th. Sulphide inclusions in the hydrocarbon are comprised of chalcopyrite and pyrite. Hydrocarbon, commonly with illite, replaces primary sandstone matrix and clastic grains. The nodules may have formed as periodic structures (cf. Liesegang rings) with precipitation from thixotropic hydrocarbon compounds. The available evidence is insufficient, however, to postulate with any certainty the origin of the hydrocarbon. It may have formed syngenetic accretions with clastic detritus or alternatively it may have been introduced after deposition of the sandstone, although no feeders have been observed.