586 SEDIMENTARY ENVIRONMENTS/Storms and Storm Deposits Figure Generalized wave modified turbidite bed Temporal history of generalized bed is shown in the triangular diagram of storm related effects (see also Myrow PM and Southard JB (1996) Tempestite deposition Journal of Sedimentary Research 66: 875 887) HCS, hummocky cross stratification have enhanced apparent cross-shelf transport Sedimentological data must therefore be combined with sequence-stratigraphical data to understand better the bed geometries and transport distances of ancient tempestites The stratigraphical distribution of tempestites may also be understood within a sequencestratigraphical framework, particularly as sea-level has a strong control on shelf profile For instance, geostrophic flow may be more common during transgressive to early highstand conditions, when accommodation space is higher and there is greater potential for Coriolis deflection, whereas more offshore-directed flow may take place during late highstand conditions characterized by greater bottom friction Tempestites are probably more abundant during late highstand to early lowstand systems tracts of third- or higherorder sequences, when sand is mobilized from the coast during relative sea-level fall Carbonate Systems Although the previous discussion applies to both carbonate and siliciclastic systems, there are also depositional features that are specific to, or most common in, carbonate systems The most abundant such features include flat-pebble conglomerate beds and shellbed accumulations Flat-pebble beds are an important component of carbonate deposits, particularly in Cambrian and Lower Ordovician strata, and are generally considered to be accumulations of intraclasts produced by the storm reworking of early-cemented carbonate in shoreline and shallow subtidal environments Detailed sedimentological analyses indicate that some flat-pebble beds were deposited from storm-generated combined flows, although it is likely that there are many other processes that could produce such beds Shell-rich grainstone tempestites accumulate as a result of winnowing by storm waves, commonly in shoreline and nearshore settings, and they have characteristics that are different from those of tempestites produced in condensed sections within maximum flooding intervals In shallow epicratonic seaways, winnowing and concentration of shell debris occurs during lowstand conditions, and further reworking and basinward transport occurs during early transgression Pronounced trends in the thickness, number, and character of shell beds occurred over the Phanerozoic, and these relate to evolutionary trends and complex taphonomic variables See Also Sedimentary Environments: Depositional Systems and Facies; Carbonate Shorelines and Shelves Sedimentary Processes: Depositional Sedimentary Structures; Particle-Driven Subaqueous Gravity Processes Sedimentary Rocks: Mineralogy and Classification; Sandstones, Diagenesis and Porosity Evolution Unidirectional Aqueous Flow Further Reading Arnott RW and Southard JB (1990) Exploratory flow duct experiments on combined flow bed configurations, and some implications for interpreting storm event stratification Journal of Sedimentary Petrology 60: 211 219 Dott RH Jr and Bourgeois J (1982) Hummocky stratifica tion: significance of its variable bedding sequences Geological Society of America Bulletin 93: 663 680 Duke WL (1990) Geostrophic circulation or shallow marine turbidity currents? The dilemma of paleoflow patterns in storm influenced prograding shoreline systems Journal of Sedimentary Petrology 60: 870 883 Einsele G (1996) Event deposits: the role of sediment supply and relative sea level changes overview Sedimentary Geology 104: 11 37 Einsele G and Seilacher A (1982) Cyclic and Event Stratification Berlin: Springer Verlag Kidwell SM (1991) The stratigraphy of shell centrations In: Allison PA and Briggs EG (eds.) Taph onomy: Releasing the Data Locked in the Fossil Record, pp 211 290 Topics in Geobiology, New York: Plenum Press Kreisa RD (1981) Storm generated sedimentary structures in subtidal marine facies with examples from Middle and Upper Ordovician of southwestern Virginia Journal of Sedimentary Petrology 51: 823 848