Sulphur isotope variations in diagenetic pyrite from core plug to sub-millimetre scales

Sulphur isotope ratio measurements (δ34S) of diagenetic pyrite are commonly used to identify S sources and mechanisms of sulphide formation in basinal sediments. This study reports such data for a diagenetic pyrite nodule from the Brent Group sandstones of the northern North Sea at three sampling scales: 50 cm (core subsample), 500 μm (laser microprobe) and 50 μm (ion microprobe). Similar δ34S variations are found by the laser and ion microprobe techniques. There is a very wide range in δ34S (<−10% to >+50%) within the nodule and isotopically heavy S (δ34S >+20%) is common at all scales. The nodule δ34S distribution does not fit a Rayleigh fractionation pattern. The laser microprobe sampling at 100–500 μm scales seems to be adequate to characterize S isotope variations in this material.