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Probable root structures and associated trace fossils from the Lower Pleistocene calcarenites of Favignana Island, southern Italy... 747
troughs between bars, are common here. Foresets of larger
bedforms in all facies associations are steep, commonly
avalanched, truncated by washouts and rip channels. These
features suggest storm-dominated sedimentation. Storm peri-
ods were separated by fair-weather intervals, during which
foresets were colonized by burrowing organisms, including
echinoids (Ślączka et al., 2011).
The trace fossils studied occur in algal and rhodolithic
calcirudites arranged in cross-bedded units up to few metres
thick. Locally, medium bedded, homogeneous, medium-
grained calcarenites enriched in pelitic material are present, as
well as coarsening-up strata, which are homogeneous in their
lower part and low-angle laminated in their uppermost part,
and topped by bioturbated calcirudites with lamination and
muddy drapes. In some places, rhodolithic conglomerates crop
out in thick beds with erosive bases, which are massive or
crudely planar cross-bedded. Moreover, lenses of calcarenite
rich in mollusc shells, up to 1.5 m thick, which display crude
lamination in their lower parts and become more chaotic up-
wards, can be found. These deposits were formed by landward
and seaward migrating subtidal dunes, which were influenced
by storms, rip currents and in some horizons, by tsunamis
(Ślączka et al., 2011).
SYSTEMATIC PART
Two taxa of root structures, tentatively interpreted as such,
root mats and three ichnotaxa of typical animal trace fossils have
been recognized. Some bioclasts from the localities studied con-
tain invertebrate borings, which are not considered in this paper.
Even if many aspects of the probable root structures remain un-
solved, the reader may benefit from their descriptions.
Faviradixus gen. nov.
D e r i v a t i o n o f n a m e. – From Favignana, the island
of occurrence of the type species, and from radix (Latin) – root.
T y p e s p e c i e s. – Faviradixus robustus distinguished
in this paper.
D i a g n o s i s. – Mostly horizontal to oblique, sparsely
branched, slightly winding tubular structure with a thick
“wall”, without swellings in the branched point and any evi-
dence of interconnections and interpenetrations.
R e m a r k s. – Faviradixus displays many similarities to
the trace fossil Rhizoichnus D’Alessandro and Iannone, 1982,
typified by Rhizoichnus firmus D’Alessandro and Iannone,
1982, from the Pleistocene of southern Italy, mainly by its thick
“wall” and configuration of some segments. However, Rhizo-
ichnus displays a more sinuous and locally helicoidal course,
and fine hair-like ducts present in the axial part. Moreover, it is isp., Thalassinoides isp., and Beaconites isp. are present
smaller (10–30 mm), and its common feature is micritization.
Faviradixus differs from Thalassinoides by convergence
upwards of the tunnels, oblique dichotomous branching
downwards, the smaller size of some branches, and a tendency
to self avoidance. The differences point to side roots of a large
tree as a possible agent. On the contrary, Thalassinoides shows
mazes or boxworks composed of tunnels of similar size (e.g.,
Ekdale, 1992).
Faviradixus robustus sp. nov.
(Figs. 3–6)
M a t e r i a l. – Holotype (Fig. 3A) – one specimen in the
Dipartimento di Geologia, Universitŕ di Palermo. Moreover,
one specimen ING UJ 183P8a (paratype; Fig. 5) in the Geolog-
ical Museum of the Institute of Geological Sciences,
Jagiellonian University. Tens of observations were made in the
field and documented by photographs.
D e r i v a t i o n o f n a m e. – From robust – sturdy in
Latin, in reference to its large size.
D i a g n o s i s. – As for the ichnogenus.
D e s c r i p t i o n. – Rarely branched, inclined to hori-
zontal, straight or slightly winding, tubular structures bounded
by a “wall”. The structure is circular or elliptical in cross sec-
tion, 40–125 mm wide, traced for at least 250 cm, forming gal-
leries. The “wall” is 4–16 mm thick. Its surface is smooth, cor-
rugated or rough or with holes, but without any ornamentation
pattern. It is composed of coarse calcarenite, without any selec-
tion or arrangement of grains (Fig. 5B). The thickness of the
“wall” is not uniform and changes around the perimeter of the
structure. The lumen is commonly slightly off-centre (Fig. 3F).
Branches are sparse, running horizontally or obliquely
down at an angle of 40–90°. They are of the same or smaller di-
ameter (Fig. 3E). The inclination of the structural segments at-
tains 30°. Dichotomous branches running obliquely down are
also present (Figs. 3A and 4A). Locally, the tubes converge in a
bench composed of 5–6 tubes, or converge obliquely up to a
central point above the recent ground surface (Fig. 3C). Very
rarely, patchy accumulations of the structures occur showing
tubes running generally outwards (Fig. 3D). The branching
tubes may run very close to each other or miss on slightly dif-
ferent levels, but never join again. They have a tendency to mu-
tual avoidance. Only rarely cross-overs can be found, but they
probably derive from different systems. In one specimen, a
“tube-in-tube” structure was found, where a smaller tube pene-
trates along a larger tube in its upper part. The tubes penetrate
along foresets and descend up to 130 cm below the modern
ground surface (Fig. 3B).
The structure described co-occurs with horizontal to
oblique and vertical galleries of the trace fossil Ophiomorpha
nodosa Lundgren, 1891, with which there are cross-cutting re-
lationships (Figs. 4A). However, it was impossible to deter-
mine the order of cross-cutting, and the characteristic granu-
lated Ophiomorpha wall was not observed in the Faviradixus
lumen. In rare cases, it seems that the Ophiomorpha wall enters
the Faviradixus “wall”, but the latter may be of diagenetic ori-
gin (see discussion of the species). Moreover, Ophiomorpha
(Fig. 4C) at the same locality.
O c c u r r e n c e. – The most abundant occurrence is at site 1
at Punta Lunga (N37°55.0686’; E012°19.219’; ±4 m; Figs. 1 and
6). A few specimens were observed at site 2 (N part of Punta
Lunga) and at site 3 (just N of the harbour in Favignana; Fig. 1).