Gravity measurements in the north Irish Sea

Abstract

This paper presents a Bouguer anomaly map of most of the north Irish Sea, based on under-water gravimeter measurements. The map incorporates earlier surveys in the northern part of the region and new work in the southern part. The new work reveals that the previously discussed Manx–Furness gravity 'low' (now renamed the East Irish Sea 'low') extends southwards to the coast of North Wales. Newly observed detailed profiles across the north-western margins of the 'low' show that it is caused by a partially fault-bounded composite sedimentary basin between the Isle of Man, Lancashire and North Wales, with a local region of basement uplift 30 km southeast of Douglas. High Bouguer anomalies are observed over a wide area between the Isle of Man, Anglesey and Ireland, suggesting a region with relatively shallow basement rocks. A negative gravity anomaly of –4o mgal amplitude occupies an elongated oblong area 40 × 30 km 2 in dimension off the east coast of Ireland near Dublin. The steep gravity gradients and other characteristics of the anomaly suggest that it is caused by a sedimentary basin about 3 to 4 km deep. The high density contrast required to explain the anomaly implies that Permo–Triassic and/or later sediments form the main infill of the basin. This anomaly is called the Kish Bank gravity 'low'.