The thickest section of Early Jurassic strata known from onshore Ireland (total Jurassic thickness 566 m) is reported from the Ballinlea-1 well (Rathlin Basin) situated on the north coast of Northern Ireland. A biostratigraphical and palaeoenvironmental assessment is presented for this section largely based on calcareous benthic microfossils (foraminifera and ostracods). The Early Jurassic Waterloo Mudstone Formation (Lias Group) of Northern Ireland has previously received little micropalaeontological attention, therefore this work provides an opportunity to enhance palaeogeographic and palaeoenvironmental understanding for the Early Jurassic of the province, and this paper illustrates the key microfossil taxa of this age from Ireland for the first time. The records, based on ditch-cuttings samples, demonstrate a stratigraphical range from Hettangian to Early Pliensbachian, consistent with other wells and boreholes in this basin. The assemblage compositions are comparable to those elsewhere in the European boreal Atlantic realm. Hettangian to earliest Sinemurian microfossil assemblages are generally of low diversity and are numerically dominated by metacopid ostracods with occasional influxes of foraminifera. Gradually, foraminiferal abundance (often dominated by species of the Lagenida) come to exceed those of the ostracods in the Early Sinemurian reaching their greatest diversity in the Late Sinemurian. The sediments are considered to represent an inner to mid-shelf environment throughout while the record thickness for this region indicates ongoing syn-sedimentary fault movement along the basin margins within this period.

从位于北爱尔兰北海岸的 Ballinlea-1 井（Rathlin 盆地）报告了爱尔兰陆上已知的早侏罗世地层的最厚部分（侏罗纪总厚度 566 m）。本节主要基于钙质底栖微化石（有孔虫和介形虫）进行生物地层学和古环境评估。北爱尔兰早侏罗世滑铁卢泥岩组（Lias Group）以前很少受到微古生物学的关注，因此这项工作为加强对该省早侏罗世古地理和古环境的了解提供了机会，本文阐述了该地区的关键微化石分类群第一次来自爱尔兰。记录，基于沟壑样本，展示了从 Hettangian 到早 Pliensbachian 的地层范围，与该盆地中的其他井和钻孔一致。组合组合物与欧洲北大西洋地区的其他地方的组合组合物相当。Hettangian 到最早的 Sinemurian 微化石组合通常具有低多样性，并且在数量上主要由 metacopid ostracods 和偶尔流入的有孔虫。逐渐地，有孔虫的丰度（通常由 Lagenida 的物种主导）开始超过早期 Sinemurian 中的介形动物，在 Sinemurian 晚期达到其最大的多样性。沉积物被认为代表了整个内陆架环境，而该地区的记录厚度表明在此期间沿盆地边缘正在进行同沉积断层运动。