The Ichnofabric Concept - Trace Fossils as Indicators of Sedimentary Environments - page 138

the resultant ichnofabric ( Fig. 2 ). Monoichnospecific ichnofabrics can yield
important insights concerning the response of benthic organisms to sedimentary
dynamics in high-energy depositional settings ( de Gibert and Goldring, 2007;
Droser and Bottjer, 1989; Nara, 1997, 2002 ).
Often, however, the situations are not so simple, as in the creation of compos-
ite ichnofabrics by the superimposition of different (successive) suites of bio-
genic structures. Commonly this occurs when a vertically tiered arrangement
of different types of burrows occurs in unconsolidated sediment ( Bromley and
Ekdale, 1986a ). That idea was expanded upon by Wetzel and Aigner (1986) ,
who likened a composite ichnofabric to a measuring stick for understanding
the magnitude and sequence of depositional and erosional events reflected in
a sedimentary deposit. Ekdale and Bromley (1991) further exemplified the
concept of composite ichnofabrics by illustrating the tiered structure of ichno-
coenoses in Late Cretaceous pelagic chalks of Denmark, where “detailed ichno-
fabric analysis reveals over a dozen successive burrowing episodes in the
Danish chalk, testifying to the fact that the original ooze passed through guts
of perhaps hundreds of organisms before it lithified” ( Ekdale and Bromley,
1991 : 232).
Another, slightly different application of the ichnofabric concept involved
the development of ichnofabric indices to describe the overall intensity of bio-
turbation that had affected a sedimentary deposit ( Droser and Bottjer, 1986,
1989 ; see Knaust, 2012 ). This approach followed earlier (pre-“ichnofabric”)
attempts to categorize bioturbated sediment on the basis of how much sediment
had been disturbed by organisms ( Reineck, 1967 ), as well as the simple recog-
nition that sediment had been burrowed without resulting in preservation of

FIGURE 2 Thalassinoides ichnofabrics. In both cases, the intense burrowing by infaunal shrimps

has completely churned the sediment, yielding a totally bioturbated—but monoichnospecific—
ichnofabric ( ii 6). (A) Modern Thalassinoides ichnofabric, produced by burrowing deca-

pod crustaceans ( Upogebia sp.) in high-intertidal sediment at Estero Morua, a macrotidal flat on the
coast of the northern Gulf of California near Puerto Pe˜asco, Sonora, Mexico. (B) Thalassinoides
ichnofabric in Pleistocene intertidal rock in a coastal outcrop in the same area as (A).

¼ 5; BI ¼