Abstract
AbstractThe genesis of polygonal faults is an intriguing diagenetic phenomenon. This study discusses their origin in carbonate mudstones together with other associated diagenetic features. In the eastern Danish Basin, at the fringe of the Baltic Sea, the Stevns peninsula offers a unique opportunity to study the early diagenesis of Upper Cretaceous Chalk deposits, buried between 500 m and 1400 m. This paper combines data from onshore and offshore high‐resolution seismic reflection profiles, a fully cored borehole with high‐resolution wireline logs and quarry and coastal cliff outcrops to study early diagenetic features at different scales. Chalk is affected by an extensive polygonal fault system that is detected in onshore and offshore seismic data. Outcrop and core data provide a better understanding of the distribution of contraction‐related features like deformation bands (hairline fractures), stylolites and fluid escape structures. An original model of genetic relationships between these different diagenetic processes is documented for Chalk. The spatial relationships between stylolites and fractures suggest that pressure‐solution processes triggered shear failure that initiated the polygonal fault systems. The early diagenetic processes affect the reservoir properties of Chalk by creating compartments and vertical connections. Taking these features into account will allow for a more detailed understanding of early diagenesis and better models for exploiting drinking water or hydrocarbons hosted in Chalk.
Highlights
Chalk is a singular material consisting principally of an accumulation of micron-sized calcareous nannofossil grains
In the eastern Danish Basin, at the fringe of the Baltic Sea, the Stevns peninsula offers a unique opportunity to study the early diagenesis of Upper Cretaceous Chalk deposits, buried between 500 m and 1400 m
This paper aimed to provide new insights into the first phases of Chalk diagenesis by untangling the complex relationship between centimetre to metre-scale observations made on a fully cored borehole with high-resolution wireline logs, on quarry exposures and on coastal cliff outcrops of the Stevns peninsula (Denmark), and 100 m-scale observations from onshore and offshore high-resolution seismic reflection profiles in the same area
Summary
Chalk is a singular material consisting principally of an accumulation of micron-sized calcareous nannofossil grains. Previous studies of the area have documented the stratigraphy, depositional facies, porosity variations with depth and the associated seismic velocities (Frykman, 2001; Lykke-Andersen & Surlyk, 2004; Stemmerik et al, 2006; Surlyk et al, 2006, 2013; Anderskouv et al, 2007; Esmerode et al, 2007; Nielsen et al, 2011).
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