An Improved Bedrock Geology Characterization in Limerick Basin Using Multi-Geophysical Data Integration Guided by Petrophysics and Outcrop Data

Abstract

Geological mapping in the Limerick Basin, Ireland, presents significant challenges due to the extensive glacial overburden obscuring the bedrock geology. To address this, multiple geophysical datasets comprising the Bouguer gravity anomaly, total magnetic intensity and resistivity depth slice at 60 m depth obtained from frequency domain electromagnetic data are integrated using a novel data integration workflow that uses geological (ground truth) and petrophysical data. The ground truth data available in this area contain information about the geological formations of outcrops and topmost geological units of drill cores procured from drilling campaigns undertaken by several mining companies.

The data integration workflow utilizes ground truth data for semi-supervised uniform manifold approximation and projection (UMAP) dimensionality reduction, which leads to cleaner separation of classes in the dimensionality-reduced data and improves the performance of the clustering algorithm for which we have used hierarchical density-based spatial clustering of applications with noise (HDBSCAN). The stochastic nature of UMAP yields slightly different results for each iteration. Hence, a repetitive workflow involving multiple iterations of UMAP and HDBSCAN is applied to create cluster maps with smoothly varying cluster labels, allowing us to classify them into ranges that are associated with geological formations and rock types using a combined interpretation technique involving geological, geophysical and petrophysical data.

The workflow is tested on a synthetic study inspired by the real geological setting of the Limerick Basin and geophysical datasets available in the area. The cluster map obtained from field data integration led to the proposal of a revised map of the area with significant modifications in the distribution of igneous and sedimentary units, specifically to the northwest and within the Limerick syncline region.