Palynological approaches to Triassic basin analysis: from the North Sea to the Barents Shelf

Introduction

A robust understanding of subsurface geology is essential for both hydrocarbon exploration and CO₂ storage. This presentation highlights CASP’s ongoing 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 on the southwest Barents Shelf. Each region represents a unique target—CO₂ storage in the Southern North Sea and hydrocarbon exploration on the Barents Shelf—yet both require refined stratigraphic frameworks to support effective resource development. Through these case studies, we illustrate the continued value of palynology, the study of organic-walled microfossils such as fossil pollen and spores, in enhancing understanding of Triassic stratigraphy.

Method

The geological contexts of the Bunter Sandstone storage complex and the Barents Shelf Triassic deposits present distinct challenges for subsurface interpretation, reflecting their differing sedimentary environments and climatic settings. In the Southern North Sea, Triassic deposition occurred primarily in dryland fluvial and lacustrine-palustrine environments (Bachmann et al. 2010; Geluk et al. 2018), which have historically been regarded as unpromising for detailed biostratigraphic studies. However, coeval sequences in Germany and Poland possess well-defined palynological zonations (e.g. Kürschner and Herngreen, 2010). This highlights a significant knowledge gap for the stratigraphy of the Southern North Sea, which currently lacks a formal, published palynozonation —the last substantial study dating back to Geiger and Hopping (1968). To address this knowledge gap, we conducted a detailed analysis of ~500 samples from 14 wells, including a previously unstudied core, that provides a near complete section through the reservoir and seal units. This analysis enabled the establishment of a refined zonal scheme for the Southern North Sea Triassic. By integrating this scheme with wireline logs, we constructed a refined chronostratigraphic framework that enhances age interpretations and significantly improves cross-border stratigraphic correlation between the UK and Dutch sectors.

In contrast, Triassic successions from the Barents Shelf region and Svalbard predominantly reflect a series of prograding deltas that infilled a shallow intra-cratonic sea, containing proven hydrocarbon reservoir and source intervals (Høy and Lundschien, 2011; Klausen et al. 2015). Previous work by CASP in the region has identified provenance-specific sand types with variable reservoir properties, (Fleming et al., 2016). While detailed biostratigraphic and sequence stratigraphic frameworks exist for the region, they lack sufficient integration. To address this, we synthesised palynological (Vigran et al. 2014; Paterson and Mangerud, 2020) and macrofossil data (Dagys and Weitschat, 1993) with the published sequence stratigraphy (Klausen et al. 2015; Gilmullina et al. 2021), creating a robust chronostratigraphic framework for 42 well and outcrop localities. This framework enabled the evaluation of various sediment input sources and spatio-temporal changes in sand types, contributing to an enhanced understanding of the depositional history and reservoir potential of the Sassendalen and Kapp Toscana groups across this vast frontier region.