Correlating Permo-Carboniferous sandstones with biogenic silica microfossils: a new biostratigraphic tool for the E&P industry

Abstract

Globally, significant oil and gas reserves occur in so-called ‘barren red beds’. These sediments are generally deposited in a shallow to non-marine environment under arid (desert) climate conditions. In terrestrial basins, biostratigraphic analysis of plant microfossils (pollen and spores) is often effective in constraining static geological models. Unfortunately, such organic-walled microfossils are not preserved in red bed deposits due to oxidation, hampering stratigraphic correlation on both local (field) and regional scale. Although red beds occur throughout the geological timescale, examples with an economic interest are the Late Carboniferous, Permian and Early Triassic of Europe (Barren Measures, Rotliegendes, Bunter − Doornenbal and Stevenson, 2010), the Triassic of the United States, and the Permo-Carboniferous of the Middle East (Melvin & Sprague, 2006). Here, for the first time, we apply biogenic silica microfossils as a stratigraphic tool in the Permo-Carboniferous red bed sequences in the Southern North Sea. The combination of their qualitative occurrence, cyclic abundance patterns, and stable isotopic data provides the possibility to improve existing regional geological correlations, position regional unconformities, and to refine reservoir architecture models. We have applied the biogenic silica stratigraphy in two representative case studies in the Upper Rotliegend in the Southern North Sea Basin. The first example focuses on refining the basin infill model of the Upper Rotliegend and the second on detecting the position of the Base Permian Unconformity (BPU). Both aspects are critical for E&P activities in the Southern North Sea but are notoriously difficult to determine due to a lack of effective correlation tools in the red bed deposits. Permo-Carboniferous red beds in