SEDIMENTARY PROCESSES/Post-Depositional Sedimentary Structures 611 Figure 12 Septarian nodule developed in mudstone with calcite filled cracks which demonstrate shrinkage of the concretion Kimmeridge Clay, Dorset, England Courtesy of R Selley bedding also occurs in periglacial sediment due to freeze–thaw action termed cryoturbation Concretions During the burial of sediment, pore water may precipitate minerals in the pore spaces In some cases, this is as pervasive cement, but, in other cases, it occurs in discrete patches around nuclei (Figure 11) In some cases, these cemented concretions or nodules occur apparently at random, whilst others follow bedding or are nucleated on obvious earlier inhomogeneities, such as fossils, burrows, or root traces Some concretions, which form at shallow burial depths in fine-grained sediment, predate major compaction and, by resisting compaction, help to preserve lamination and delicate fossils that would otherwise be flattened beyond recognition Other early concretions (e.g., calcrete nodules) are an integral part of soil textures and are discussed elsewhere (see Soils: Modern; Palaeosols) Most concretions occur during deeper burial and many have distinctive internal features ‘Septarian nodules’ have internal cracks filled with calcite, reflecting shrinkage during their development (Figure 12) Other concretions have complex nested conical fractures, termed ‘cone-in-cone structure’ See Also Sedimentary Processes: Depositional Sedimentary Structures; Deep Water Processes and Deposits; Particle- Driven Subaqueous Gravity Processes Soils: Modern; Palaeosols Trace Fossils Further Reading Allen JRL (1982) Sedimentary Structures: Their Character and Physical Basis Developments in Sedimentology 30A & B, pp 593, 663 Amsterdam: Elsevier Allen JRL (1985) Principles of Physical Sedimentology, ch 10 London: Allen & Unwin Collinson JD (2003) Deformation structures and growth faults In: Middleton GV (ed.) Encyclopedia of Sediments and Sedimentary Rocks, pp 193 195 Dordrecht, Kluwer: Academic Publishers Collinson JD (1994) Sedimentary deformational structures In: Maltman A (ed.) The Geological Deformation of Sediments, pp 95 125 London: Chapman & Hall Collinson JD and Thompson DB (1989) Sedimentary Structures, 2nd edn., ch London: Chapman & Hall Jones ME and Preston RMF (eds.) (1987) Deformation of Sediments and Sedimentary Rocks Special Publica tion of the Geological Society, London, 29 London: Geological Society Leeder MR (1982) Sedimentology; Process and Product, ch 11 London: Allen & Unwin Leeder MR (1999) Sedimentology and Sedimentary Basins, ch 12 Oxford: Blackwell Science Mutti E (1992) Turbidite Sandstones Milan: Agip Pettijohn FJ and Potter PE (1964) Atlas and Glossary of Primary Sedimentary Structures Berlin: Springer Reineck HE and Singh IB (1980) Depositional Sedimentary Environments, 2nd edn Berlin: Springer Selley RC (2000) Applied Sedimentology, 2nd edn., ch San Diego: Academic Press