Gigantoproductid brachiopod storm shell beds in the Mississippian of South China: implications for their palaeoenvironmental and palaeogeographical significances

1. IntroductionStorm beds are distinct facies criteria on shelves and ramps, which are generated by storm winds, such as cyclones and hurricanes in tropical latitudes and blizzards in middle and high latitudes (Tucker & Wright, 1990; Flugel, 2004). Ager (1973) defined storm beds as tempestites that are commonly characterized by sharp and erosional base, internal structures including accumulations of shells, graded and flat bedding and parallel and cross lamination, and ripple bedding and burrowing presented at the top part (Aigner, 1985; Flugel, 2004; Dattilo et al., 2012). Tempestites are abundant and widely distributed in carbonate environments during the Phanerozoic (e.g. Einsele & Seilacher, 1982; Flugel, 2004). The sedimentary patterns and biotic distributions of tempestites could provide important information in aspects of their depositional process, palaeoenvironment, palaeogeographical location and even stratigraphic comparison (Johnson, 1989; Lehman & Pope, 1989; Flugel, 2004; Jin et al., 2013). Storm shell beds, which are one common type of tempestites and featured by accumulation of shells, were documented during the icehouse periods of the late Ordovician (Lehman & Pope, 1989; Davis, 1999; Jin et al., 2013), early Silurian (Johnson, 1989; Li & Rong, 2007; Jin, 2008) and early Carboniferous (Jeffery & Aigner, 1982; Butts, 2005) and during greenhouse climate, as in the middle Ordovician (McFarland et al., 1999), late Permian (Simoes & Kowalewski, 1998), early Triass