Lower Jurassic (Hettangian–Pliensbachian) microfossil biostratigraphy of the Ballinlea-1 well, Rathlin Basin, Northern Ireland, United Kingdom

Ian Boomer*, Azrin Azmi, Philip Copestake, Robert Raine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
JournalProceedings of the Geologists' Association
DOIs
Publication statusAccepted/In press - 2020

Bibliographical note

Funding Information:
The authors acknowledge the support of the Geological Survey of Northern Ireland for providing access to the Ballinlea material. Azrin Azmi acknowledges the financial support of Ministry of Higher Education Malaysia and the National University of Malaysia while undertaking a PhD at the University of Birmingham. The paper benefitted from the assistance of Mark Jeffs (MSci student, (Birmingham) and the advice of Michael Simms (National Museums Northern Ireland) and Nigel Ainsworth (PalaeoDate Ltd) at various stages, including review. We also thank one anonymous reviewer. Philip Copestake thanks Merlin Energy Resources Ltd for their support in undertaking this work. Robert Raine carried out work under the SLA between the Department for the Economy and the British Geological Survey and publishes with the permission of the Department and the Executive Director of the British Geological Survey (UKRI).

Funding Information:
The authors acknowledge the support of the Geological Survey of Northern Ireland for providing access to the Ballinlea material. Azrin Azmi acknowledges the financial support of Ministry of Higher Education Malaysia and the National University of Malaysia while undertaking a PhD at the University of Birmingham. The paper benefitted from the assistance of Mark Jeffs (MSci student, (Birmingham) and the advice of Michael Simms (National Museums Northern Ireland) and Nigel Ainsworth (PalaeoDate Ltd) at various stages, including review. We also thank one anonymous reviewer. Philip Copestake thanks Merlin Energy Resources Ltd for their support in undertaking this work. Robert Raine carried out work under the SLA between the Department for the Economy and the British Geological Survey and publishes with the permission of the Department and the Executive Director of the British Geological Survey (UKRI).

Publisher Copyright:
© 2020 The Geologists' Association

Keywords

  • Foraminifera
  • Hettangian
  • Ostracoda
  • Pliensbachian
  • Sinemurian
  • Waterloo Mudstone Formation

ASJC Scopus subject areas

  • Geology
  • Palaeontology

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