Organic maturation levels, thermal history and hydrocarbon source rock potential of the Namurian rocks of the Clare Basin, Ireland

Vitrinite reflectance data from two inland cored boreholes confirm high mat uration levels throughout the onshore part of the Irish Glare Basin and sug gest erosion of 2 to 4 km of late Carboniferous cover and elevated palaeoge othermal gradients in the Carboniferous section. The observed maturation gr adients are fully consistent with the published hypothesis of a late Carbon iferous/Permian 'superplume' beneath Pangaea but local vertical reversals i n gradients also suggest a complex thermal regime probably involving advect ive heating. The uppermost Visean-lower Namurian Glare Shale is laterally e xtensive and up to 300 m thick. Although this unit is post-mature, TOC valu es of up to 15% suggest that it could have considerable hydrocarbon source rock potential in any less mature offshore parts of the basin. (C) 1999 Els evier Science Ltd. All rights reserved.