Palaeobiological and palaeonvironmental significance of the Pliocene trace fossil Dactyloidites peniculus ALFRED UCHMAN and PETER PERVESLER Uchman, A. and Pervesler, P. 2007. Palaeobiological and palaeonvironmental significance of the Pliocene trace fossil Dactyloidites peniculus. Acta Palaeontologica Polonica 52 (4): 799–808. The radial trace fossil Dactyloidites peniculus occurs in a deep tier in totally bioturbated shoreface sediments of Pliocene age in the Stirone Valley, N Italy, together with Thalassinoides isp. and Ophiomorpha nodosa. Long, narrow shafts run− ning from centre of the radiating structure and abundant faecal pellets in the radial structure were discovered. The trace maker of D. peniculus, probably a polychaete, deposited the pellets deeply in the sediment, probably for reinforcement of the tubes and a gardening of microbes for feeding. This trace fossil exclusively occurs within a narrow horizon at the top of a shallowing−up section interpreted as a high−stand system tract, below a discontinuity surface capped by finer sedi− ments. D. peniculus was formed in soft sandy sediments under stable conditions related to the latest phases of the high− stand system tract. Therefore, it is a candidate for indication of similar environmental situations having a soft sandy, but stable sea floor. Key words: Tracefossils,Dactyloidites, gardening, sequence stratigraphy, marine flooding, foredeep, Neogene, Pliocene. Alfred Uchman [[email protected]] Institute of Geological Sciences, Jagiellonian University, ul. Oleandry 2a, PL−30−063 Kraków, Poland; Peter Pervesler [[email protected]] Department of Palaeontology, University of Vienna, Althanstrasse 14, A−1090 Vienna, Austria. Introduction fill related to the Southern Alps and Apennines. The Late Pliocene sediments are interpreted as a regressive succession Dactyloidites peniculus, a radial trace fossil, has been de− deposited in the transition from outer to inner shelf (Domi− scribed by D’Alessandro and Bromley (1986) from Pleisto− nici 2001, 2004). cene shallow marine sediments of southern Italy. New field The Upper Pliocene–Lower Pleistocene sections along the observations of this trace fossil (second occurrence) from Late Stirone river valley have been investigated since the sixties Pliocene sediments in Emilia Romagna, Italy, are reported in with regard to their sedimentology, palaeoecology, micro− this study. This trace fossil occurs in a strictly defined horizon palaeontology, taphonomy and sequence stratigraphy (Pelosio in a shallowing−up sequence, what implies a narrow ecologi− 1960, 1964; Papani and Pelosio 1962; Pelosio and Raffi 1974, cal range. New morphological details, for instance a long ver− 1977; Iaccarino 1996; Mutti 1996; Molinari 1997; Mutti et al. tical shaft or the presence of faecal pellets, and the palaeo− 2000; Dominici 2001, 2004). However, there is not much in− environmental context shed new light on this poorly known formation about ichnology, although Dominici (2001) men− ichnospecies. A morphological and palaeoenvironmental ana− tioned some trace fossils. lysis of D. peniculus is the main aim of this paper. The studied trace fossil occurs in the 48.8–51 m interval in The Stirone section was studied during campaigns in July the more than 75 m−thick Stirone section (Figs. 1, 2). This sec− and September 2005 and September 2006. tion can be subdivided in two units separated by a discontinu− ity at 51 m of the section. The lower part of the lower unit con− Institutional abbreviation.—INGUJ, Institute of Geological sists of very fine−grained sands and silty very fine−grained Sciences, Jagiellonian University, Krakow, Poland. sands with intercalated layers containing molluscs, mainly bi− valves in convex up orientation. The middle part of the unit displays similar grain sizes but is characterised by an increase Geological setting of shell and plant debris. The upper part of the lower unit shows a slight coarsening and a decreasing silt content up to The Late Pliocene to early Pleistocene sediments in the the discontinuity surface, which is covered by a thick silt inter− Western Emilia Romagna (Parma and Piacenza provinces) val (Fig. 3). Sediments below the discontinity are generally to− were deposited in the northwestern extension of the palaeo− tally bioturbated, except for the upper part where a few layers Adriatic Sea. They are part of the Po Plain−Adriatic Foredeep show a primary lamination. Acta Palaeontol. Pol. 52 (4): 799–808, 2007 http://app.pan.pl/acta52/app52−799.pdf 800 ACTA PALAEONTOLOGICA POLONICA 52 (4), 2007 Brooksella Walcott, 1896 and Haentzschelinia Vialov, 1964 Po River Piacenca in this ichnogenus and recognized three ichnospecies of Dac− tyloidites: D. asteroides Fitch, 1850, D. canyonensis Bassler, Arda River 1941, D. ottoi (Geinitz, 1849). D. peniculus D’Alessandro and Castell´Arquato Stirone River Bromley, 1986, and D. cabanasi (Meléndez in Cabanás, 1966) Scipione Ponte Parma (see Gámez Vintaned et al. 2006 for the latter) were distin− Salsomaggiore Terme guished latter. Fürsich and Bromley (1985) interpreted Dacty− loidites as a structure produced by worm−like organisms hav− 111 ing a proboscis used for reworking sediment from a central Section Stirone r e 75 m v i shaft. R It seems that trace fossils described under Dactyloidites 158 n e S t i r o Hall, 1866 require a revision. First of all, the type material of 124 Section Stirone San the type ichnospecies (Lower Cambrian of New York State), 0m Nicomede 143 which displays only a few rays of uneven width (see Häntz− schel 1975: fig. W88.7), requires a revision, but this was never 136 done. Vialov (1989) expressed his opinion that Haentzsche− Riverbed Forests linia Vialov, 1964 should be excluded from Dactyloidites sensu Fürsich and Bromley (1985), foremost because of the Scipione fact that the radial elements of Haentzschelinia, in contrast to Ponte 0 500 1000 2000 m those of Dactyloidites, are numerous and of constant width. Vialov (1989) argued also that Dactyloidites is much larger and Fig. 1. Location of the study area in the Stirone river valley close to San Nico− mede (Province of Parma, Italy). Arrows “Section Stirone 0 m” and “Section that its type material is confined to the Cambrian. Also Schwei− Stirone 75 m” point to the base and the top of the section shown in Fig. 2. gert (1998) separated Haentzschelinia and Dactyloidites on the basis that Dactyloidites is a fully radial star−shaped trace fossil and Haentzschelinia forms commonly only a half or three The interval with the trace fossil Dactyloidites peniculus quarters of a star. The diagnosis of Dactyloidites by Fürsich (48.8–51.00 m) is exclusively composed of very fine, com− and Bromley (1985) accentuates spreiten, however in D. peni− pletely bioturbated sand. The deep−tier trace fossil D. peni− culus (see the diagnosis and description below) only spreite− culus is filled mainly with fine−grained pelleted material. like structures are present. It is not excluded that the diagnosis Ophiomorpha, which occurs together with Dactyloidites dis− of Dactyloidites should be amended or D. peniculus should be plays a distinct wall, was produced in shifting sediment be− ascribed to different ichnogenus. All these problems are, how− fore formation of the discontinuity surface. The interval con− ever, beyond the scope of this paper and cannot be resolved tains a Thalassinoides boxwork that reaches deep into the without re−evaluating the type material of Dactyloidites. sediment below the discontinuity (Figs. 2, 3). The horizontal portions of Thalassinoides do not show any wall and they are Dactyloidites peniculus D’Alessandro and Bromley, only slightly compacted. These facts suggest that the Thalas− 1986 sinoides was produced in an already compacted sediment. It Figs. 4–6. is very probable that the Thalassinoides boxwork was for− med starting from the discontinuity surface. The boxwork *1986 Dactyloidites peniculus isp. nov.; D’Alessandro and Bromley 1986: 79, pl. 12: 3; pl. 13: 3. was partially cemented during sedimentation of higher sedi− ments. Chlamys layers, shell debris layers and a horizon with Amended diagnosis.—Simple, numerous and crowded cylin− transported but well−preserved Glycymeris shells cover the drical elements radiating laterally from a central shaft. They discontinuity surface. More than 11 metres of overlying silt form a radial pile arranged in a part or full circle brush−like and sandy silt with Pinna characterize a rising sea−level of a structure. The radial elements consist of tubes that can over− new depositional sequence. lap and form spreite−like structures. The tubes can be lined and irregularly coated with pellets. Material.—7 specimens, 5 thin sections, and numerous field Systematic ichnology observations documented by 88 photographs. Description.—A radial structure, which appears as an oblate Ichnogenus Dactyloidites Hall, 1866 ellipsoid of revolution in outline. It is 82 to 270 mm wide Type ichnospecies:?Buthotrephis asteroides Fitch, 1850; Lower Cam− (mean value 115.6 mm) and 42 to 120 mm high (mean value brian, New York State, USA. 77.3 mm). The radiating elements are thin, 4–5 mm thick, Diagnosis.—Vertical radial spreiten structure having central straight to curved, unbranched tubes. The tubes can coalesce, shaft (Fürsich and Bromley 1985). especially in their proximal parts (Figs. 4B, 5A). In vertical Remarks.—The ichnogenus Dactyloidites Hall, 1866 was re− section, the tubes may overlap partially and appear as indis− interpreted by Fürsich and Bromley (1985). They included tinct spreiten. The tubes run from the common centre. Some UCHMAN AND PERVESLER—PLIOCENE TRACE FOSSIL DACTYLOIDITES 801 Fig. 2. Schematic section showing the distribution of sediments types, body and trace fossils. Dactyloidites peniculus occurs close below the sequence boundary from 48.8 to 51.0 m. Grain size: Si, silt; Fs, fine sand; Cs, coarse sand. http://app.pan.pl/acta52/app52−799.pdf 802 ACTA PALAEONTOLOGICA POLONICA 52 (4), 2007 SequenceSequence boundaryboundary 0 1 2 33mm Sequence boundary 51 D D D D D D TThalassinoideshalassinoides bboxworkoxwork D Oph D D 50 Oph D D Oph D D D D Oph D D Oph D Oph Fig.