Enhancing subsurface understanding through palynostratigraphy: insights from the Triassic of the Southern North Sea and Barents Shelf

A robust understanding of subsurface geology is crucial for both effective hydrocarbon exploration and CO₂ storage. This presentation highlights CASP’s research on two significant Triassic stratigraphic successions: the Bunter Sandstone Storage Complex (Bacton and Haisborough groups) in the Southern North Sea, and the Sassendalen and Kapp Toscana groups of the southwest Barents Shelf. Through these case studies, we demonstrate the application of palynology, the study of organic-walled microfossils such as fossil pollen and spores, to enhance subsurface understanding.

The Bunter Sandstone Storage Complex in the Southern North Sea and the Triassic formations of the southwest Barents Shelf represent important targets for CO₂ storage and hydrocarbon exploration, respectively. The geological settings of these regions fundamentally differ as do the challenges of their subsurface interpretation.

Southern North Sea Triassic deposition predominantly occurred in dryland fluvial/lacustrine-palustrine environments. These apparently ‘unpromising’ settings mean that there have been very few studies of Triassic biostratigraphy, despite detailed zonations for coeval deposits in Germany and Poland. This presents a significant knowledge gap that we have addressed by analysing samples from 12 onshore and offshore wells in the UK and Dutch sectors as part of a broader study of the Bunter Sandstone Storage Complex. By integrating palynological data with wireline logs and other geological information, we have developed a comprehensive chronostratigraphic framework. This framework provides refined age interpretations for reservoir and seal units and significantly enhances cross-border correlations.

The Barents Shelf Triassic succession represents deltaic and shallow marine sedimentation where detailed sequence stratigraphic and biostratigraphic schemes do exist, but where they have typically been poorly integrated. For our Barents Shelf study, we integrated published palynological and macrofossil data with wireline log-based sequence stratigraphy. This approach enabled the construction of a robust chronostratigraphic framework, instrumental in assessing spatio-temporal changes in provenance-specific sand types within the Sassendalen and Kapp Toscana groups. The framework provides valuable insights into the depositional history and sedimentary dynamics of the Barents Shelf, advancing our understanding of Triassic reservoir potential across the region.

The contrasting depositional and climatic settings of the Southern North Sea and Barents Shelf during the Triassic underscore the need for tailored approaches to palynological sampling and processing, as well as the development of regional biozonal schemes. Despite these differences, our research reveals intriguing parallels in the response of terrestrial plants to environmental changes during the Triassic. Significant episodes of species turnover commonly coincide with marine transgressions and climatic perturbations, highlighting the sensitivity of Triassic ecosystems to such changes. This interplay between climate, sedimentation, and palynological dynamics emphasises the intrinsic connection of these factors in shaping depositional settings and informing subsurface models.

Our results demonstrate the continued relevance of traditional techniques like biostratigraphy, specifically the value of palynology, in developing stratigraphic models across various depositional settings. This presentation illustrates how combining palynostratigraphy with wireline analyses can improve the characterisation of both hydrocarbon plays and CO₂ storage complexes, highlighting the importance of these techniques in building subsurface models. Furthermore, the approaches and findings of this research are relevant to other Triassic successions, including those of the East Irish Sea Basin and adjacent areas, and the Central North Sea, demonstrating their broader applicability.