Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 629

Scolicia ( Figs. 2 Fand 5 B) is a large, bilaterally symmetrical, subcylindrical
pascichnion filledwithmeniscate lamellae, broadly divided into two concave sets.
The basal face shows a faint bilobate morphology with two strings and the upper
face a slight axial groove. In transverse cross sections, the concentric structure
of the bilobate lamellae is the most conspicuous feature. Scolicia is produced
by Spatangus -like irregular echinoids. For discussion, see Uchman (1995a) .
Thalassinoides ( Figs. 2 G and 5 A-C) is a burrow system consisting of
horizontally branched tunnels connected to the surface by more or less vertical
shafts; swellings often occur at points of branching. A typical asymmetrical
(eccentric) fill structure often results from active filling by the burrowing organ-
ism or collapse of the burrow walls. The tubes are 5-20 mm in diameter and
smooth-walled. Thalassinoides is interpreted to be produced by crustaceans.
For further details, see, for example, Frey et al. (1984) , Ekdale (1992) , and
Schlirf (2000) .
Trichichnus is a thread-like, rarely branching, cylindrical burrow commonly
exceeding 20 cm in length. Its fill is usually pyritized. For further details, see
McBride and Picard (1991) and Uchman (1995a, 1999) .
Zoophycos ( Fig. 2 I) is a spreiten structure composed of distinct levels or
coilings and/or lobes. The regular fill structure appears as crescent-shaped
en-echelon features in vertical section. The presence of open (collapsed) or
actively filled marginal tubes indicates lower or higher oxygen contents, respec-
tively, in the surrounding waters (e.g., Wetzel and Werner, 1981 ). For further
details, see Bromley and Hanken (2003) .

5. ICHNOFACIES
The ichnofacies model was introduced by Seilacher ( 1964, 1967 ; Fig. 3 )to
distinguish between the different trace-fossil associations that characterize con-
tinental, shallow- and deep-marine deposits, so-called molasse-type deposits in

FIGURE 3 Ichnofacies from shelf to deep sea (modified after Uchman, 2007a ).