Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 627

4. POST-DEPOSITIONAL TRACE FOSSILS
Chondrites ( Figs. 2 A, H and 5 A-C) is a three-dimensional, regularly branching
tunnel system consisting of an open connection to the surface and numerous
tunnels that ramify at angles of 30-60 to form a dendritic pattern. Chondrites
is interpreted as a deep-tier chemichnion (for discussion, see Fu, 1991; Uchman,
1999; Wetzel, 2008 ).
Dictyodora ( Fig. 2 B) is a meandering to looping deep-tier pascichnion com-
posed of a basal subcylindrical structure and a dorsal crest. Dictyodora is
reported only from Paleozoic deep-sea sediments. For discussion, see Benton
and Trewin (1980) .
Nereites ( Fig. 2 C) is a winding to regularly meandering, more or less hor-
izontal pascichnion, consisting of a median back-filled tunnel enveloped by an
even to lobate zone of reworked sediment. Synonyms of Nereites are post-
depositional Helminthoida and probably pre-depositional Spirophycus ( Uch-
man, 1995a ). Modern Nereites missouriensis is produced in spatial relation
to the redox boundary,

1-2 cm above the Fe-Mn-stained horizon ( Wetzel,

2002 ).
Ophiomorpha ( Figs. 1 F and 2 E, G) comprises variably oriented, branched
cylinders, locally with a granulated wall interpreted to be produced by crusta-
ceans. In post-Tithonian deep-sea sediments, O. annulata and O. rudis occur.
O. nodosa is typical of shallow-marine sediments. For discussion, see
Tchoumatchenco and Uchman (2001) , Uchman (2001, 2009) , and Cummings
and Hodgson (2011a) .
Palaeophycus is a branched or unbranched, smooth or ornamented, lined,
essentially cylindrical, predominantly horizontal burrow of varying diameter;
the fill is passive, typically structureless and of the same lithology as the host
rock. These burrows are interpreted as pascichnia or domichnia. For discussion,
see Pemberton and Frey (1982) and Keighley and Pickerill (1995) .
Phycosiphon ( Figs. 2 D and 5 C) consists of compound antler-like arranged
series of spreiten. A spreite is a laminated biogenic structure composed of
closely spaced successive tunnel margins produced as the burrow shifts laterally
through the sediment. The width of a single spreite is 1-5 mm, and the diameter
of the marginal tube is 0.5-1 mm. The marginal tubes show a thin lining.
Phycosiphon is interpreted as a fodinichnion. For discussion, see Wetzel and
Bromley (1994) , Naruse and Nifuku (2008) , and Bednarz and McIlroy (2009) .
Planolites ( Figs. 2 H and 5 C) consists of rarely branched, straight or gently
curved, inclined or horizontally oriented, cylindrical tunnels, commonly filled
with sediment of different lithology. Differences in diameter, penetration depth,
and sediment infill may allow different types to be distinguished ( Wetzel,
1981 ). Active filling of the burrow is indicated by grain-size differences in
relation to the surrounding sediment and relatively close packing of the infill.
Planolites is interpreted as a pascichnion. For further details, see Pemberton and
Frey (1982) and Keighley and Pickerill (1995) .