Fig. 3
From: Timing and origin of natural gas accumulation in the Siljan impact structure, Sweden
Appearance and paragenesis of solid bitumen and seep oil. (a–d) from sedimentary rock fractures (e–g) from crystalline rock fractures. Drill core photographs are shown in (a, c, e) and SEM images of secondary minerals on the fracture surfaces (BSE mode) are shown in (b, d, f, g). a White limestone (VM2:328 m) with abundant solid bitumen (asphaltite = “Asph”) and oil seep. b Abundant scalenohedral calcite (13C-rich) crystals on the fracture in (a), and small patches of bitumen (“Asph”). c Fractured section of limestone (01–10C:326 m) with abundant occurrences of solid bitumen and oil seep. d Euhedral calcite (13C-rich) crystals on the fracture in (a) with abundant bitumen and seep oil smeared on the surface. e Drill core sample VM1:255 m (fractured crystalline rock). f Euhedral pyrite and bitumen on the fracture surface (e). g Bitumen (“Asph”) and calcite (slickensided and partly euhedral crystals) in an adjacent fracture, VM1:251 m. Length of scale bars: (a, c, e) 4 cm, (b, f, g) 500 µm, (d) 1 mm
