Mixed Siliciclastic/Carbonate Systems

The ichnology of mixed siliciclastic/carbonate successions, in which sediment admixture has had a clear effect on infaunal populations, is discussed. Fundamental influences that allow for the development of unique ichnological signatures in mixed systems include grain size, grain shape, and early diagenetic alteration. Shell debris within dominantly siliciclastic successions introduces complexities into the infaunal habitat that are clearly reflected in trace-fossil assemblages. Some differences are preservational, with trace fossils inherently more difficult to recognize in coarser bioclastic intervals than in fine-grained siliciclastic intervals. Faunal level differences include those where some taxa are excluded by admixed bioclastic detritus or by reduced ecospace availability. Diagenetic processes in mixed systems also operate at different scales and temporal intervals, leading to fundamental differences in preservation and in substrate consistency. In mixed systems, quintessential carbonate ichnotextures co-occur with prototypical siliciclastic ichnotextures, such as successions with interstratified or coplanar firmground and hardground assemblages.