Abstract: Many siliciclastic reservoirs contain millimetre-scale diagenetic and structural phenomena affecting fluid flow. We identified three major types of small-scale flow barriers in a clastic Rotliegend hydrocarbon reservoir: cataclastic deformation bands; dissolution seams; and bedding-parallel cementation. Deformation bands of various orientations were analysed on resistivity image logs and in core material. They are mainly conjugates, and can be used to validate seismically observable faults and infer subseismic faults. Bedding-parallel dissolution seams are related to compaction and post-date at least one set of deformation bands. Bedding-parallel cementation is accumulated in coarser-grained layers and depends on the amount of clay coatings. Apparent permeability data related to petrographical image interpretation visualizes the impact of flow barriers on reservoir heterogeneity. Transmissibility multiplier calculations indicate the small efficiency of the studied deformation bands on flow properties in the reservoir. Deformation bands reduce the host-rock permeability by a maximum of two orders of magnitude. However, host-rock anisotropies are inferred to reduce the permeability by a maximum of four orders of magnitude. The relative timing of these flow barriers, as well as the assessment of reservoir heterogeneities, are the basis for state-of-the-art reservoir prediction modelling.

Abstract: Four specimens of the pterosaur Pteranodon exhibit patterns of irregular alternating light and dark bands on the lateral surfaces of the upper jaw anterior to the nasoantorbital fenestra. Examinations reveal that the maxilla and premaxilla of Pteranodon consisted of two thin sheets of bone interconnected by regularly spaced septa with the spaces contained within presumably pneumatized, resulting in a structure analogous to modern honeycomb sandwich panels. The alternating light and dark bands resulted from waves of bone deposition moving anteriorly along the external surface of the lateral sheet of bone and laying down thin laminae of new bone while bone was simultaneously resorbed from the internal surface of the lateral sheet to maintain its thickness. The specimens that exhibit the bands were immature males and no banding was found in mature specimens or immature females. Therefore, the presence of the bands in immature males is interpreted as correlated with the enlargement and reshaping of the rostrum as males approached and attained sexual maturity.

Thin, planar, dark, lamination-like bands are found in host siltstones in the Miocene-Pliocene metamorphosed Miura-Boso accretionary prism, southern Boso Peninsula, Japan. We classified the bands into four types on the basis of distribution, crosscutting relations, and internal textures. Type 1-1 dark bands are developed parallel to the bedding plane and do not include crushed or deformed grains within the band. Type 1-2 bands are also developed parallel to the bedding plane, but grain alignment within the band cuts obliquely across that in the host rock. Type 2 bands include ductilely deformed grains similar to an S-C′ structure, whereas type 3 bands have cataclastic grains. All the dark bands except type 1-1 (being an open fracture with little displacement) are shear bands or slip planes formed from sedimentation to accretion, although the formation mechanisms between the four types are different. These deformation bands are affected by the state of consolidation and magnitude of stress during formation, reflecting the deformation processes. Type 1-1 bands show evidence of independent particulate flow from excess pore-fluid-pressure generation, which occurs just after sedimentation. Type 1-2 bands are flexural-slip faults formed during formation of folds; type 2 bands are sliding planes formed from submarine landslides, whereas type 3 bands are thrust faults formed during accretion.