Doctoral defence: Sylvester Ikenna Ofili “Geochemistry and depositional environments of two black shale formations: the Baltoscandian Cambrian-Ordovician Alum Shale and the Cretaceous Lokpanta Oil Shale“

On 17 June at 14.15 Sylvester Ikenna Ofili will defend his doctoral thesis “Geochemistry and depositional environments of two black shale formations: the Baltoscandian Cambrian-Ordovician Alum Shale and the Cretaceous Lokpanta Oil Shale“ for obtaining the degree of Doctor of Philosophy (in Geology).

Supervisors:
Visiting Professor Alvar Soesoo, University of Tartu and Tallinn University of Technology
Professor Leho Ainsaar, University of Tartu

Opponent:
Associate Professor Jurga Lazauskiene, Vilniuse Ülikool (Leedu)

Summary:
Black shales are widespread globally, offering valuable insights into Earth's geological history. Various environmental factors, sedimentation rate and seawater composition, influence their formation. Notable examples of black shales include the Paleozoic Alum Shale in Northern Europe and the Cretaceous Lokpanta oil shale in Nigeria. Both shales contain high levels of organic matter and useful elements, making them attractive for metal and hydrocarbon exploration. In this work, the Alum Shale and Lokpanta oil shale were studied to understand better their geochemistry and depositional environment and to model the element distribution and accumulation mechanisms.

A study of mineral composition shows that the Alum Shale is rich in quartz, K-feldspar, and K-mica/illite minerals, making up to 95% of its composition, whereas the Lokpanta oil shale has lower K-feldspar but abundant in carbonates (calcite and dolomite) which comprise half of its composition. Both shales are enriched in uranium (U), molybdenum (Mo), and vanadium (V). The Alum Shale (graptolite argillite) in Estonia shows higher enrichment in these metals than the Lokpanta shale, particularly in the basal part of the bed. This variation may be influenced by the slow sedimentation rate of the organic-rich mud during its deposition in the marine environment with little or no oxygen. While the Lokpanta oil shale was also deposited under oxygen-depleted conditions, the sedimentation rate was much higher than in the Alum shale. This difference may have contributed to the enrichment of U, Mo and V in both shales.

The bulk of the materials that make up both shales were eroded from rocks of intermediate to felsic composition and/or older sediments and deposited on a passive margin setting. Indicators of the degree of chemical weathering suggest that these materials in Alum shale and the Lokpanta oil shale have experienced intense and moderate–intense weathering, characteristic of warm and humid paleoclimate.