SEPM Strata

ichnofacies

The concept of ichnofacies was developed by Adolph Seilacher (1967) (among others) at Tubingen University. This approach is used as a paleontological tool to analyze assemblages of trace fossils to determine ancient depositional settings and facies of sedimentary rocks. These facies were initially defined as assemblages of ichnofossils related by Seilacher (1967) to bathymetry. Since Seilacher's original publication he and like minded scientists have established that ichnofacies are also sensitive to sediment dynamics, coherence of the sediment, salinity, oxygen levels and predation. Each of the ichnofacies on the diagram below are named after a distinctive trace fossil often (but not always) present in that assemblage. These ichnofacies have been related to contemporaneous trace fossils found in modern settings (see Frey and Pemberton, 1985). The substrate character determines the ichnofacies assemblage that colonizes it (see the Seilacher diagram below) and has been divided by Steve Hasiotis into:

Soupground: Slurry
Softground: Grains in contact, but wet
Firmground: De-watered, compacted
Hardground: Cemented

These assemblages of biogenically controlled sedimentary structures, where preserved intact, are closely related to depositional setting. For this reason ichnofacies are commonly used as stratigraphic tools that consider the suites of trace fossils & fossils as sedimentologic & paleontologic indicators that can be identified & analyzed to help interpret vertical ichnological successions. The figure below, copied from Pemberton et al, (1992a), illustrates a vertical association of ichnofacies that matches the facies successions of a shoreline.

Tiering or vertical stacking of ichnofacies layers with a bed or a series of beds can form basis of unraveling more detailed depositional interpretations (see link in side bar).

ichnofacies are also used where substrate-controlled ichnofacies colonize sequence stratigraphic discontinuity surfaces. These ichnofacies, like glossifungites on firmgrounds, often mark the boundaries between parasequences. Thus the original depositional unit below (with or without softground burrowing) may be eroded by a transgression and the surface produced has a postdepositional ichnofacies assemblage then superimposed on it.

For more information on this topic the reader is referred to the Ichnology Research Group (IRG) at the University of Alberta, in Edmonton Canada lead by George Pemberton; link by clicking on the IRG Logo to left.

Some References
Frey, Robert W., and S. George Pemberton (1985), Biogenic Structures in Outcrops and Cores. I. Approaches to Ichnology, Bulletin of Canadian Petroleum Geology, Vol. 33 No. 1, Pages 72-115

Seilacher, A. 1967 Bathymetry of trace fossils Marine Gology v 5 p 413-428