SEDIMENTARY ENVIRONMENTS/Depositional Systems and Facies 491 where local channel bases are nested within a largerscale palaeovalley However, deeper incision as a result of base-level fall may cause the erosion surface to cut down into facies that differ from those beneath autocyclic channel bases Outside the confines of an incised valley, the long-term emergence of the sedimentary surface and the resulting nondeposition may allow highly mature soil profiles to develop, so that recognition of palaeosol facies in interfluve areas may have widespread stratigraphical significance Non-erosive sharp contacts at the bases of coarser facies may also indicate that regressions were forced by falling base level Falling base level or relative sea-level, therefore, may be manifested in a variety of different ways leading to uncertainty in discrimination and correlation Rises of base level or relative sea-level produce more uniform facies expressions, as they tend to be associated with transgression and a cut-off of sediment supply to more distal settings owing to sediment being trapped closer to its source The results are flooding surfaces (Figure 3) characterized by condensation, often to the point of nondeposition In marine settings, such surfaces are commonly characterized by intense bioturbation, reflecting the increased time available for animals to rework the sediment before burial When flooding occurred in humid near-emergent settings, peat developed as plant productivity balanced increasing accommodation space Coal seams, the compacted products of peat, may be of local or regional significance Where flooding occurred through autocyclic processes, for example by cut-off of sediment supply through distributary switching on a delta plain, the seam extent reflects the area of an interdistributary bay or floodplain lake Where the control was allocyclic, coal seams may be regionally important stratigraphical markers Flooding surfaces, however expressed in the sediments, commonly mark the bases of coarsening-up units, termed parasequences, that record the progradations that eventually filled the resulting bodies of water Where flooding is associated with the transgression of a high-energy shoreline, the transgressive surface may be an erosional pebble lag ravinement surface, separating nearshore sediment below from more offshore sediment above See Also Sedimentary Environments: Alluvial Fans, Alluvial Sediments and Settings; Deltas Sedimentary Processes: Depositional Sedimentary Structures; Post-Depositional Sedimentary Structures; Aeolian Processes Sedimentary Rocks: Mineralogy and Classification Sequence Stratigraphy Soils: Palaeosols Trace Fossils Further Reading Anderton R (1985) Clastic facies models and facies analysis In: Brenchley PJ and Williams BPJ (eds.) Sedi mentology: Recent Developments and Applied Aspects, pp 31 47 Special Publication 18 London: Geological Society Galloway WE (1989) Genetic stratigraphic sequences in basin analysis Architecture and genesis of flooding surface bounded depositional units Bulletin of the American Association of Petroleum Geologists 73: 125 142 Leeder MR (1999) Sedimentology and Sedimentary Basins Oxford: Blackwell Scientific Nichols G (1999) Sedimentology and Stratigraphy Oxford: Blackwell Scientific Reading HG (ed.) (1996) Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd edn Oxford: Blackwell Scientific Publications Reading HG (2001) Clastic facies models, a personal per spective Bulletin of the Geological Society of Denmark 48: 101 115 Scholle PA and Spearing D (eds.) (1983) Carbonate Depos itional Environments Memoir 33 Tulsa: American Association of Petroleum Geologists Scholle PA, Bebout DG, and Moore CH (eds.) (1983) Sand stone Depositional Environments Memoir 31 Tulsa: American Association of Petroleum Geologists Selley RC (1996) Ancient Sedimentary Environments and their Subsurface Diagnosis, 4th edn London: Chapman & Hall Tucker ME (1985) Shallow marine carbonate facies and facies models In: Brenchley PJ and Williams BPJ (eds.) Sedimentology: Recent Developments and Applied Aspects, pp 147 169 Special Publication 18 London: Geological Society Walker RG and James NP (eds.) Facies Models; Response to Sea Level Change Waterloo, Canada: Geological Society of Canada