Hemipelagic and Pelagic Basin Plains - Trace Fossils as Indicators of Sedimentary Environments - page 662

variable diameter; the fill is typically structureless and of the same lithology as
the host rock.
Phycosiphon ( Fig. 3 ) is an extensive, small-scale spreite trace fossil consist-
ing of repeated narrow, U-shaped lobes enclosing a spreite at millimeter- to
centimeter-scale, branching regularly from an axial spreite of similar width.
Lobes are protrusive, mainly parallel to bedding.
Planolites ( Figs. 3 and 4-7 ) represents an unlined, rarely branched, straight
to tortuous, smooth to annulated, tubular burrow of variable dimensions. The fill
is essentially structureless but differs from the host rock.
Scolicia ( Figs. 3, 5 B and 6 B) is a large, bilaterally symmetrical, subcylin-
drical burrow with meniscate lamellae often divided into two concave sets.
In transverse cross section, a concentric structure of bilobate lamellae surrounds
an eccentric axis. Today, Scolicia is produced by irregular echinoids that prefer
to live in sandy to silty sediment.
Skolithos ( Figs. 3 and 8 B) is a straight, simple, unbranched, normally ver-
tical tube with a uniform diameter (4-10 mm).
Spirophyton ( Fig. 3 ) consists of a spirally coiled outward, slightly bent-
upward spreite around a central axis. The diameter of the coils increases down-
ward regularly.
Spongeliomorpha ( Fig. 3 ) is a 3D burrow system composed of cylindrical
tubes with Y- and T-shaped branching with enlarged junctions, having mm-long,
irregularly oriented casts of scratches (bioglyphs) along the burrow margin.
Taenidium ( Figs. 3 and 7 E) represents an unlined or very thinly lined, simple,
straight to sinuous, cylindrical burrow with a fill of meniscus-shaped segments.
Teichichnus ( Fig. 3 ) is a vertical, blade-like elongate spreite burrow result-
ing from the upward or downward displacement of the causative tube.
Thalassinoides ( Figs. 3, 4-7 and 8 B) is an endichnial or hypichnial, slightly
winding, semi-circular, straight or curved, branching burrow system having
swellings at Y- or T-shaped junctions.
Trichichnus ( Fig. 3 ) represents a vertical to oblique, straight or slightly
winding, rarely branched cylindrical burrow, up to 1 mm in diameter.
Zoophycos ( Figs. 3, 4-7 and 8 ) is an endichnial, horizontal to subhorizontal
planar spreiten burrow visible as lobes. The lobes are surrounded by a marginal
tunnel. Fine spreiten laminae run obliquely according to the concavity of the lobe
or as a subcircular, helical coiled structure and may contain poorly outlined pel-
lets. Spreiten laminae are slightly curved and run from the elevated center toward
a thin, indistinct marginal tunnel, where they tend to curve.
3. DEPOSITIONAL ENVIRONMENTS AND TRACE FOSSILS
The biogenic sedimentary structures can be used to decipher the environmental
conditions by looking at a specific trace fossil characterizing a typical condition
(index trace fossil) or at the ichnofabric as such. The combination of both
attempts will provide maximum information.