The Ichnofabric Concept - Trace Fossils as Indicators of Sedimentary Environments - page 136

one developed on a sedimentary surface) may reflect substantial changes with
the passage of time. Ignoring any of the many threads that are woven together in
a sedimentary deposit will yield an incomplete, or possibly misleading, view of
the geological history and paleoenvironmental significance of that deposit.
Beginning only about three decades ago, the ichnofabric approach is a rel-
atively young direction in ichnology, although its roots can be traced back a few
decades further to the neoichnological studies of the German scientists Rudolf
Richter, Wilhelm Sch¨fer, and Hans-Erich Reineck at the Senckenberg Institute
in Wilhelmshaven (see Baucon et al., 2012 ). Based on experiments and obser-
vations in the North Sea, Sch¨fer (1956) noticed that benthic organisms modify
the sediment in many different ways, which can lead to total sediment homo-
genization ( Fossitexturae deformativae ) with subsequent overprinting and pres-
ervation of discrete burrows ( Fossitexturae figurativae ). Reineck (1958)
applied these features to delineate the amount of reworking in tidal deposits,
and subsequently documented biologically generated sediment fabrics in com-
bination with other primary sedimentary features based on box-core samples
from the North Sea shelf Reineck (1963) . He also developed a semiquantitative
scheme for estimating relative amounts of bioturbation in such samples, a
method that has subsequently been adapted in ichnofabric analysis (see discus-
sion of the bioturbation index in Knaust, 2012 ). Refinement of the box-core
sampling procedure allowed for the collection and detailed description of bio-
genic sedimentary fabrics in modern deposits ( Reineck et al., 1967 ). In the
1970s, this methodology was expanded and refined by the use of X-ray radio-
graphy to carry out neoichnological studies, especially along the Georgia coast
of North America ( Howard and Elders, 1970; Howard and Frey, 1975 ).
Also in the 1970s, trace fossils and complex sedimentary fabrics resulting
from burrowing were beginning to be recognized and documented in thoroughly
bioturbated sediment in deep-sea cores ( Berger et al., 1979; Chamberlain, 1975;
Ekdale, 1977, 1978; Ekdale and Berger, 1978; Van der Lingen, 1973; Warme
et al., 1973 ). Accompanying those descriptive investigations of ichnological
features in cores were analytical attempts to quantify the nature and extent of
vertical mixing of pelagic sediment by burrowing organisms in the deep sea
( Berger and Heath, 1968; Guinasso and Schink, 1975 ), because that aspect of
ichnology has direct implications for the sharpness (or fuzziness) of biostrati-
graphic horizons based on microfossils. Observations in deep-sea box cores
led to the interpretation of a three-tiered vertical stratification (mixed layer, tran-
sition layer, and historical layer) of burrow emplacement in deep-sea pelagic
deposits ( Berger et al., 1979; Ekdale et al., 1984b ). Wetzel (1981, 1983, 1984,
1985) interpreted the ecological and stratigraphical significance of biogenic sed-
imentary structures in box cores of modern deep-sea sediments, and he outlined
their characteristic position in vertical tiers within the sediment.
Following the aforementioned seminal investigations, the concept of ichno-
fabric per se was born in the 1980s and grew out of a need to decipher a meaning
from the results of bioturbation and/or bioerosion in situations where