Hemipelagic and Pelagic Basin Plains - Trace Fossils as Indicators of Sedimentary Environments - page 658

trace fossils mainly penetrate deeply and cross previously deposited beds (see
also Seilacher, 1962 ). Continuously deposited sediments contain only post-
depositional burrows, while graphoglypids are overprinted by organisms bur-
rowing deeper. However, in (hemi)pelagic settings, pre-depositional burrows
may be preserved below ash layers (e.g., Manville and Wilson, 2004 ). Grapho-
glyptids are addressed in detail by Uchman and Wetzel (2012) .
2.3 Systematic Ichnology
Only post-depositional burrows are described briefly here because they com-
monly occur and dominate in (hemi)pelagic deep-sea deposits ( Fig. 3 ). In most
cases, the producers of deep-sea trace fossils are unknown and of unknown
taxonomic affinity. In practice, most of the trace fossils mentioned here are
observed on cut or parting surfaces as 2D structures, particularly in cores. Rec-
ognition of their 3D aspects, being a prerequisite for their proper identification,
can be difficult (see Ekdale et al., 1984 , for linking 2D views to 3D models).
Alcyonidiopsis is an endichnial, simple, almost straight, strongly flattened
cylindrical burrow, mostly a few millimeter wide, filled with very small
elongate fecal pellets.
Asterosoma ( Fig. 3 ) consists of elongate, several centimeter long, a few cen-
timeter wide bulbous segments having a terminal or eccentric, laminated fill;
the segments are oriented (sub)horizontally and are arranged around a central
vertical, somewhat twisted axis. Asterosoma occurs in impure mud containing
some silt and fine sand.
Chondrites ( Figs. 3 and 4-7 ) represents a regularly bifurcating tunnel sys-
tem consisting of a (small number of) master shafts open to the surface, which
ramify at depth to form a dendritic network.
Nereites ( Figs. 3, 5 D and 7 D) is a usually selectively preserved, winding to
regularly meandering, often horizontal trail, consisting of a central back-filled
tunnel enveloped by an even to lobate zone of reworked sediment. Commonly,
only the external part of the enveloping zone is preserved as a densely packed
uni- or multiserial chain of small depressions or pustules.
Palaeophycus ( Figs. 3 and 4 A) is a typically unbranched, smooth or orna-
mented, lined, essentially cylindrical, predominantly horizontal burrow of
staining resulting from local dissolution and precipitation of iron (see Hartmann, 1979 for details).
(B) RV Sonne Cruise 114, core 20 (11 54 0 N, 118 04 0 E, 2,919 mwater depth; fresh core). (C) RV Sonne
Cruise 140, core 03 (15 25 0 N, 115 5 0 E, 4248 mwater depth; X-ray radiograph negative; 1-8 cm). (D)
Institute of Geosciences Kiel, core 13209-2 (12 29.2 0 N, 20 02.7 0 W, 4,713 m water depth;
726-740 cm; X-ray radiograph negative); carbonate shells (white dots) within Zoophycos document
a temporary surface-feeding of the producer while the sediment was deposited just below the carbonate
compensation depth where CaCO 3 dissolution occurs on the sediment surface. (E) Institute of
Geosciences Kiel, core 10148-1 ( 8 40 0 N, 149 30 0 W; 5,100 m water depth; X-ray radiograph
negative; 619-630 cm); note that Chondrites cross-cut Zoophycos . m, mottled homogeneous surface
layer; rb, redox boundary (stained by Mn-Fe-oxides; appearing light in X-ray radiograph negatives);
Ch , Chondrites ; Pa , Palaeophycus ; P , Planolites ; Th , Thalassinoides ; Z , Zoophycos .