Trace fossils and palaeoenvironments in the Ecca group of the Nongoma Graben, northern Zululand, South Africa

Because of the lack of body fossils and the generally poor exposure of the Ecca Group in the Nongona Graben, northern Zululand, trace fossils provide useful evidence of the environment and conditions of deposition in addition to that derived from sedimentological criteria. Trace fossils occur repeatedly at specific levels within coarsening-upward deltaic sequences within the lower and upper parts of the succession, but unlike previous studies their distribution appears to be largely independent of bathymetry. On the lower delta plain interdistributary bay-fill sequences appear to contain the greatest abundance and diversity of trace fossils, and in terms of Seilacher's (1967) bathymetrically controlled ichnofacies include both shallow-water (Skolithos, Diplocraterion) and deep-water (Helminthopsis) forms. Scolicia occurs at lower levels in the sequence within the prodelta deposits and Planolites in the deep-water offshore shales. Both forms, however, are “facies crossing” ichnogenera and would not be expected to be restricted to any particular ichnofacies or depositional environment. The scarcity of trace fossils in the shales probably reflects the generally inhospitable conditions within the basin which restricted faunal development.