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Establishing the glacial record of the Port Askaig Tillite Formation (Cryogenian) in Argyll (lecture)

Thursday, 12 April 2018
7:30 pm - 9:30 pm
Event Category:
Lecture Theatre, Gregory Building
c/o School of Geographical & Earth Sciences
Glasgow, Glasgow City G12 8QQ United Kingdom

Dr Tony Spencer

The Port Askaig Formation (PAF) in the Garvellach Islands and Islay is ~1100 m thick and includes 47 diamictite beds, interbedded with siltstones, dolostones and sandstones. The succession in the PAF records a total of 76 climatically-related stratigraphic episodes: 28 glacial, 25 periglacial and 23 non-glacial episodes. The PAF occurs in a Dalradian succession that is many kilometres thick, as newly revealed by sea-floor mapping around the Garvellachs. Compared with other Cryogenian glacial successions around the World, the PAF is exceptional in its combination of formation thickness, the number of climatically-related stratigraphic episodes, and the considerable thickness of its host supergroup. These indicators of relative stratigraphic completeness suggest that the base of the PAF in the Garvellachs is a succession without a major break, supporting it as a candidate section for the base of the Cryogenian System (GSSP).

Study of the ‘PAF’ has a long history which started with MacCulloch (1819). It was the first Neoproterozoic glacial deposit to be identified (Thomson 1871) and the wonderful outcrops in the Garvellachs were first ‘discovered’ by Pitcher and Shackleton (1961), leading to my Memoir in 1971. Now a large team is working to prepare a new Memoir for 2021.

Further reading: SPENCER, A.M. (1971): Late Precambrian Glaciation in Scotland. Geological Society, London, Memoir 6, pp. 5-102.

Tony has been a practising professional geologist since completing his PhD at Liverpool University in 1966 on the Port Askaig Tillite Formation in the Garvellachs and Islay. Whilst employed at the Geological Society of London researching Mesozoic-Cenozoic orogenic belts, he was the author of the 1971 GSL Memoir number 6 – an exhaustive treatise on the Port Askaig Tillite, which today remains the key reference for the stratigraphy of that area; and he also published another definitive paper on the stromatolitic carbonates of the overlying Bonahaven Formation.

A long and distinguished career in the oil industry then followed, first with BP and latterly with Statoil in Norway, where he published and edited a large number of key papers, books and memoirs on the petroleum geology of the Arctic regions, the NW European continental margin and the North Sea. Throughout his career in the oil industry he maintained his interest in the Precambrian glacial story and published a paper on NE Greenland.

He retired from Statoil in 2012 after a career in petroleum exploration spanning 41 years and rather than just relaxing and enjoying retired life in Norway; he has turned back to his first love, the Port Askaig Formation. He spends a lot of his retirement in a remote and primitive bothy on the Garvellachs and is in the process of authoring several key papers on the area including a proposal for a ‘Golden Spike’ on the Garvellachs to mark the worldwide base of the Cryogenian Period of the late Precambrian – which if accepted would be only the second such ‘spike’ in Scotland (after Dob’s Linn).

Before the lecture, Dr Spencer will be presented with the T. Neville George Medal for services to stratigraphy in recognition of his work on Precambrian glaciations, in particular his work on the Port Askaig Tillite on Islay and the Garvellachs.