The following chemostratigraphy study was completed on the Permo–Carboniferous Unayzah Group in Eastern Saudi Arabia. The aim of the study was to determine whether the technique could be used to identify formation and member boundaries on a subregional scale, with the area extending for c. 550 km in a NW–SE direction and 350 km NE–SW. A total of 30 375 core and cuttings samples were analysed from 225 wells using ICP (Inductively Coupled Plasma) and XRF (X-ray Fluorescence) instruments, with data acquired for 42–53 elements for each sample in the range Na-U in the periodic table. Of these, details of 14 wells are discussed in the present work.

Based on variations in Zr/Ti, Zr/U, Zr/Y, Y/U, U/Th, Gd/Zr, Nb/Yb and Nb/Th it is possible to identify a hierarchical order of one zone, four subzones and five divisions, these chemozones being correlative on a subregional scale. By comparing geochemical, biostratigraphic, sedimentological and wireline log data in selected reference wells, it was possible to relate chemozones to particular members of the Unayzah Group. The differences in geochemistry between these chemozones/members is largely explained by changes in provenance, though depositional environment may have exerted at least some influence.

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