Regional geochemical comparisons from the Lower Palaeozoic, Southern Uplands-Down-Longford terrane in Northern Ireland and Scotland

Abstract

Newly-acquired regional geochemical data for the Down-Armagh (Northern Ireland) sector of the Southern Uplands–Down-Longford terrane are assessed by comparison with the equivalent dataset for southern Scotland. Despite the much thicker glacigenic cover to the Down-Armagh bedrock, the principal geochemical lineaments identified in the Southern Uplands are still apparent. Patterns of element distribution emphasize the continuity of structure and stratigraphy between the two regions, with Cr, Zr, Sr, Rb, Ba and Ca (as CaO) proving particularly instructive. Much of the Down-Armagh outcrop consists of Llandovery strata from the Gala and Hawick Groups, so it is this part of the terrane that is most closely considered. Though continuity is clear, there is a suggestion of additional structural imbrication in Down-Armagh, whilst variability in the defining element ratios suggests along-strike compositional changes in the turbidite sandstones. These changes may be controlled by lithostratigraphical variation in sedimentary provenance, or may be influenced by the dominant palaeocurrent flow towards the SW, which has resulted in a broadly more distal and mature Llandovery turbidite lithofacies in Down-Armagh than in the Southern Uplands