LOWER CARBONIFEROUS (DINANTIAN) STRATIGRAPHY AND STRUCTURE IN THE KINGSCOURT OUTLIER, IRELAND

Logging of 55 recent boreholes, together with remapping, has resulted in a fundamental reassessment of the stratigraphy and sedimentology of the Dinantian Kingscourt Outlier. Despite the present isolated positi on of the outlier within the Longford-Down Massif, the Kingscourt rock s are an integral part of the Dublin Basin succession. The newly defin ed Ardagh Platform marks the most northerly limit to basinal sedimenta tion in the Dinantian Dublin Basin. The Courceyan is a typical but thi nner, north Dublin Basin succession with two new formal units: the Roc kfield Sandstone Member and the Kilbride Formation. The latter, a coar se-grained, well washed limestone of latest Courceyan to early Chadian (late Tournaisian) age is the shallow water equivalent of the Feltrim Formation (Waulsortian facies), which is absent in the outlier. The C ourceyan interval in the north of the outlier is markedly attenuated. In the succeeding Chadian-Brigantian interval basinal facies predomina te in the south, but on the Ardagh Platform an almost complete coeval Visean shallow water sequence is found. A new platform unit (Deer Park Formation) of latest Asbian to Brigantian age is defined in the Ardag h area. The Dee Member (Chadian) is newly defined for the lower part o f the basinal Tober Colleen Formation and the Altmush Shale Member is formally defined for the upper part of the Loughshinny Formation. Two major structures dominate the Kingscourt Outlier: the NE-SW trending M oynalty Syncline in the south and the N-S trending Kingscourt Fault. B oth are Hercynian structures, but probably represent reactivated Caled onide basement-controlled structures. Dinantian syn-depositional fault ing is indicated in both the Courceyan ('Kingscourt Sag') and Chadian- Asbian. The latter period of faulting in the Ardagh area separates pla tform facies in the north from basinal facies to the south. In the lat e Asbian, platform facies with carbonate build-ups prograded south int o the basin as far south as Nobber, but in the latest Asbian to Brigan tian, basinal facies extended northwards over the collapsed platform m argin.