Irregular cavities found in muddy intertidal to supratidal carbonate sediments. They take a number of forms: birdseye fenestrae (irregular, ‘birdseye’-shaped cavities, usually 1–5 mm across, formed by gas entrapment in the sediment); laminoid fenestrae (long, thin cavities, parallel to the sediment laminae, formed particularly in algal, laminated muds, and produced by the decay of organic material); and tubular fenestrae (cylindrical, near vertical tubes, formed by burrowing organisms or plant rootlets). Fenestral cavities may become filled with sparry calcite (sparite). If they remain unfilled, the fenestrae are responsible for the development of fenestral porosity in the sediment. The term comes from fenestra (pl. fenestrae), the Latin for an opening or window.
Subjects: Ecology and Conservation — Earth Sciences and Geography.