(Albian) shell-armoured and associated echinoid trace fossils from the Sa´caras Formation, Serra

13 Pages·2005·0.88 MB·English

1 Lower Cretaceous (Albian) shell-armoured and associated
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3 echinoid trace fossils from the Sa´caras Formation, Serra Gelada
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5 area, southeast Spain
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PAOLO MONACO, ALICE GIANNETTI, JESU´S E. CARACUEL AND ALFONSO YE´BENES
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Monaco, P., Giannetti, A., Caracuel, J.E. & Yebenes, A. 2005 00 00: Lower Cretaceous
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(Albian)shell-armouredandassociatedechinoidtracefossilsfromtheSa´carasFormation,
12 SerraGeladaarea,southeastSpain.Lethaia,Vol.38,pp.1–13.Oslo.ISSN0024-1164.
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The Sa´caras Formation (Albian, Lower Cretaceous) of the Serra Gelada succession
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(Prebetic of Alicante), southeast Spain comprises carbonate-rich, upwards thickening
15 parasequencesinwhichmanytypesoftracefossilshavebeenidentified.Thepresentstudy
16 focuses on two types of tubular trace fossil characterized by features of their external
17 coating.Thefirsttypeisrepresentedbyashell-covered,structuredtracefossil,upto4cm
in diameter and 40cm in length, built horizontally, from rectilinear (type 1) to gently
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curved(type2),whichenvelopesanunstructuredpipeofgreysiltysediment.Thecoating
19 is characterized by imbricated, flat particles, mainly orbitolinid foraminifers and other
20 planarbioclasts,formingthinconcentriclayers;incrosssectionthebioclastsproducea
typicalplumedstructure.Thistracefossilrepresentsanewichnogenusandichnospecies,
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herenamedEreipichnusgeladensis.Particlearrangementoftheexternalcoatingissimilar
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tothatofterebelloidtubes,butEreipichnusisahorizontaltracefossil,whereasstructured
23 wormtubesarevertical.Thesecondtypeisagrain-coatedtracefossil,tubularinshape,
24 with a simple internal structure. The coating is often reddish with respect to the
neighbouring dark grey sediment and shows a slightly coarser-grained texture, which
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envelopes the internal muddy pipe. This type, which yielded echinoids, was produced
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by irregular or heart-shaped sea-urchins (spatangoids) and is attributed to Scolicia or
27 Cardioichnus.FaciesanalysisoftheSerraGeladasuccessionwithEreipichnusandScolicia
28 orCardioichnuslocallyshowsothertypesofbranchedtracefossils(primarilyrepresented
by different forms of Thalassinoides) and bioturbation is developed in tiers, increasing
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upwardsinabundanceanddiversity.&Cardioichnus,Ereipichnus,Ichnology,Imbricated
30 tracefossils,LowerCretaceous,Prebetic,Scolicia,Spain.
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32 PaoloMonaco[[email protected]],&AliceGiannetti,DipartimentodiScienzedellaTerra,
piazzadell’Universita`I-06100Perugia,Italy;Jesu´sE.Caracuel[[email protected]],and
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AlfonsoYe´benesDipartimentoCienciasdelaTierraydelMedioAmbiente,Fac.Ciencias,
34 Univ. Alicante, Apdo. 99 San Vicente del Raspeig, E-03080 Alicante, Spain; 27th March
35 2004,revised31stJuly2005.
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38 The structure of grain-coated trace fossils is well (Onuphidae, Oweniidae and Terebellidae) contain
39 established in the ichnologic literature but a tidy species thatactivelypick upshellsandheavyparticles
40 arrangement of gravel-oriented particles is rarely above the sediment surface (Fager 1964; Bromley
41 observed and only few examples of unbranched, 1996; de Gibert 2003). The construction of coated
42 coarse-grained trace fossils preserved as full relief tubes (e.g. the tube-building polychaete Lanice in
43 structures have been described (Seilacher 1964; intertidalsands;Carey1987)mayhelptostabilizethe
44 Roniewicz1970;Bromley1996;deGibert2003).Many substrate in sandy sea-floor against water movement
45 marine organisms are able to pick up sand-sized caused by wave surges, rip currents or spring tides
46 particles from the substrate in order to construct (Fager 1964). Myers (1972) described a similar rein-
47 and reinforce their burrows, but far fewer taxa forcement of the upper portion of a vertical tunnel
48 stack tabular shells or flat skeletal grains to produce produced by the terebelloid worm Diopatra cuprea.
49 imbricated structures (Fager 1964; Hallam 1970; In this case only the upper portion of tube (tube
50 Bromley 1996; de Gibert 2003). cap 2–5cm long), which is built at or above the
51 In shallow-water marine settings, several families sedimentsurface,showsthecharacteristiccamouflage-
52 of annelid worms build frameworks to produce shell- reinforcementcomprisingflatshellsandrockfragments
53 armoured vertical tubes (tube-building polychaetes, or algae (see also the trace fossil Lepidenteron of
54 terebelloid tubes). Among worms only three families terebelloid worms, Suhr 1988). It is noteworthy that
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DOI10.1080/00241160500355277#2005Taylor&FrancisGroupLtd
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2 P. Monacoet al. LETHAIA 38(2005)
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Fig. 1. The study area and position of the Serra Gelada section, Alicante area, southeast Spain. Units C2–C6 and G4–E are lithological
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subdivisions:C5–C6arereferredtotheLowerCretaceousSa´carasFormation(Fig.2;afterYe´benes2004).
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92 individuals of some polychaetes such as Owenia by coarse-grained particles. In particular taxa of
93 fusiformisandLaniceconchilegaarenotrandomlydis- Opisthognatidae use the mouth and select shells or
94 tributed,butlumptheirburrowstogetherduringcon- coarse-grained particles to reinforce the walls of
95 ditionsofstrongripplecurrentsortides.Theperiodof their deep vertical tunnels (von Frisch 1975).
96 rapidgrowthinOweniacoincideswiththetime(spring) In the geological record, examples of shell-
97 of phytoplankton bloom (Fager 1964; Carey 1987). armoured and well-structured coated trace fossils
98 Therefore,densepopulationsofshell-armouredtubes are rarely encountered. Two types are described from
99 may reflect a peak in the worm-population density the Middle Jurassic of Oxfordshire (England) and
100 formedunderunidirectionalcurrents. referred respectively to Diopatrichnus roederensis and
101 A count of dark and light particles on each tube Diopatrichnus odlingi, indicating their close resem-
102 indicates that Owenia worms must have handled blance to Diopatra tube caps (Kern 1978; de Gibert
103 about 25,000 sand or shell grains per centimetre of 2003). An additional type has now been observed in
104 eachtube(Fager1964).Thesizeofgrainsmaychange the Lower Cretaceous (Albian) succession from the
105 in relation to the size of the burrowing organism Serra Gelada section (Prebetic of Alicante), Spain
106 (in the case of juvenile Owenia, vertical tubes reach (Fig. 1) and is here erected as a new ichnogenus and
107 lengthsof15cmandheavymineralgrainsreachinsize ichnospecies Ereipichnus geladensis (see Appendix).
108 upto80m)buttheparticlesareattachedinamanner, The trace fossil is horizontal and tubular in shape.
109 sothattheresultingtubeisimbricatedupwards.Even The cross section reveals a coating made up by a
110 fishes can create vertical tunnels, which are coated concentric, coarsening-outward pattern composed of
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LETHAIA 38(2005) Albian shell-armoured andassociated echinoidtrace fossils from Spain 3
111 skeletalfragments,whichareimbricatedandarranged 3. Nodular and bioturbated bioclastic limestones
112 in several thin layers. An unsolved problem concerns (packstones). Bioclasts are abundant and diverse
113 the identity of organisms that could build such a includingbivalves,crinoids,gastropods,bryozoans,
114 type of horizontal tube because all previously known echinoids, and rodophytes.
115 grain-coated structured tubes are vertical and do not 4. Bioclastic rudstones and grainstones with some
116 develop on the horizontal bedding plane (de Gibert ooids, forming plano-convex, cross-stratified
117 2003). calcarenitic beds, more or less bioturbated.
118 This paper presents the first ichnological analysis Fragmentary and occasionally oriented bioclasts
119 from the Serra Gelada section. The ichnoassemblage include bivalves, crinoids, gastropods, bryozoans,
120 recorded in the Serra Gelada area is composed of algae, benthic foraminiferans and rare echinoids.
121 Ereipichnus geladensis and non-imbricated, grain-
These lithofacies are organized in upwards
122 coated trace fossils, which are produced by irregular
coarsening-, thickening- and carbonate-rich para-
123 (heart-shaped) sea-urchins (spatangoids) and are re-
sequences, in which bioturbation increases in abun-
124 ferred to the ichnogenera Scolicia and Cardioichnus.
dance and diversity from facies 1 to 3.
125 Different types of Thalassinoides – typical Ophiomor-
126 pha – are also present, but only in the coarse-grained
127 calcarenitic beds.
Methods
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The Lower Cretaceous (Albian) trace fossils from
130 Study area: geological and
the Serra Gelada area have been studied in terms
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stratigraphical setting of their preservation (full or hemirelief) and three-
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dimensional development in marly and calcareous
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The trace fossils described here were analyzed in a beds. Three-dimensional orientation of tubes and
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well-exposedsectioncroppingoutintheSerraGelada their relationship to the bedding have been analyzed
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area(Figs1,2;Ye´benes1996,2004).TheSerraGelada alongwiththedegreeofflatteningduetocompaction.
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area is located northeast of Alicante and between the Measurements of theorientations areplotted as rose-
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baysofBenidormandAltea(Fig.1).Theareabelongs diagrams on Fig. 2, which gives clear evidence of the
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to the northeastern part of the Internal Prebetic uni-directionalorientationofthetracefossilsandalso
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Domain (also named Prebetic of Alicante), corre- shows the stratigraphic distribution of ichnoassem-
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sponding to the (para-) autochthonous sector of the blages. The external shape and framework have been
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ExternalZoneoftheCordilleraBe´tica(deRuig1992). considered and ichnofabric has been analyzed in the
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Upper Jurassic–Lower Cretaceous sedimentary field including also observations from large fallen
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rocks are well exposed in the Serra Gelada area and blocks along the coastal cliff. Trace fossils have been
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the succession is up to 800m thick. The succession studied in transverse and longitudinal sections to
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is subdivided into seven lithostratigraphic units document the structure of the external tube and
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(Ye´benes 2004) of which the uppermost part yielded internal pipe (Fig. 3). Skeletal grain arrangement has
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the trace fossils of this study and is assigned to been observed in thin sections. In cases where echi-
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theSa´carasFormation(LowerCretaceous,Fig.2).The noids have been found preserved within the trace
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formation consists of mainly marls, calcarenites and fossils, grain distribution and colour in the external
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irregularly bedded limestones, about 200m thick and the internal part of the trace fossil have been
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(units C5and C6of Ye´benes 2004;Fig. 1). According defined.
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to biostratigraphic analysis this portion is referred to
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Lower – Middle Albian (Granier 1987; Castro 1998).
154 Grain-coated trace fossils
Four different litho-facies can be distinguished:
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156 1. Arenaceous and calcareous grey marlstones. Based on the structure and shape of trace fossils it is
157 Bioclasts are abundant, consisting of thin-shelled possible to distinguish between two grain-coated
158 bivalves, planktonic foraminifers and Orbitolini- types, whose morphological affinities are discussed:
159 dae;echinoidsarefrequentmainlyinthelowerpart (1) imbricated shell-armoured (structured), and (2)
160 of the unit. grain-coated (unstructured).
161 2. Alternating calcareous marls and bioturbated
162 nodular marly limestones, composed of bioclastic
(1) The shell-armoured trace fossils (structured)
163 wackestones and packstones. Echinoids, bivalves,
164 rare ammonites and belemnites are the most Description of specimens in the type area. – Shell-
165 frequent but fragmentary bioclasts also occur. armoured (structured) trace fossils appear in
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Fig.2.DetailedlogoftheSa´carasFormation,whichistheupperpartoftheSerraGeladasuccession,Alicantearea,southeastSpain.Horizons
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withshell-armouredtracefossilsandechinoid-richlevelsareshown.Theorientationofshell-armouredtracefossilsisindicatedbytherose
220 diagrams.
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LETHAIA 38(2005) Albian shell-armoured andassociated echinoidtrace fossils from Spain 5
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248 Fig.3.Generalviewofshell-armouredtracefossilsEreipichnusgeladensis(Albian,LowerCretaceous),SerraGeladasection,Alicantearea,
southeastSpain.&A–B.Slightlymeandering,horizontaltubes(10to40cminlength)ofEreipichnusgeladensis(type2).&C–D.Rectilinear
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tubes of Ereipichnus geladensis (type 1) packed on superimposed layers showing subcircular or slightly elliptical (ovoid) cross-sections.
250 Meniscatestructuresandinternalmuddypipeareseldompreserved(seearrowinCandD,respectively).
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253 horizontal full relief, well cemented and tubular in mainly orbitolinids and well-sorted, flat fragments
254 shape, between 10 and 40cm in length, and sub- of bivalve and gastropod shells, along with other,
255 circular or slightly elliptical (ovoid) in cross-section more or less platy, carbonate and siliciclastic grains.
256 (Fig. 3A–D). Diameters range from 2 to 4cm, most A transverse section of the lined trace fossil (Fig. 4B)
257 frequently 2.5cm. The degree of eccentricity of the revealsaconcentric, coarsening-centrifugal patternof
258 transversesection(calculatedashorizontalvs.vertical skeletal fragments. Grains of the shell-armoured tube
259 diameter) ranges from 1 (circular) to 4 (elliptic). change in size from fine-grained sand (0.03 to
260 Frequently, trace fossils are more flattened in the 0.1mm),intheinnerpartclosetotheinternalrod,to
261 marly beds, showing a planar base and a convex verycoarse-grainedsand(0.5to1.5mm),intheouter
262 top (Fig. 4A). Most (95%) of the trace fossils are portion of trace fossil (Fig. 4D–F). Grains are aligned
263 horizontallydistributedandparalleltobedding,rarely defining curved, conical laminae, which are con-
264 (5%) gently inclined forming a 20–30(cid:1) angle with centrically placed around the axis with progressively
265 respect to the stratification (Fig. 3C). In the stratifi- increasing angles from 10–15(cid:1) (close to the internal
266 cation plane, they range from rectilinear (type 1) to rod) to 80–90(cid:1) (close to the outer part) (Fig. 4D–F).
267 slightly meandering or gently curved (type 2), Imbrication of grains is clearly visible in the internal
268 changing their direction of locomotion at most 35(cid:1). lumen floor where flat particles are tangentially dis-
269 In some beds they form sinuous mazes (Fig. 3A–B) posed (as a tiled floor). Close to theinternal channel,
270 developed horizontally and distributed on super- particles are concentrically stacked (Fig. 4E–F); this
271 imposedlayers,moreorlessstrictlypackedaccording particular disposition of grains forms, in longitudinal
272 to lithology and trace fossil abundance (Fig. 3C–D). section, a characteristic plumed structure (Caracuel
273 Imbricationofgrainsisthemostimportantfeature et al. 2002).
274 of these trace fossils (Fig. 4D–F). It is shown by the Locally, the coarse-grained framework shows
275 distribution of tabular-shaped skeletal particles, convex structures, similar in shape to meniscate
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Fig.4.Coatingstructuresofshell-armouredtracefossilEreipichnusgeladensis(Albian,LowerCretaceous),SerraGeladasection,Alicantearea,
314 southeastSpain.&A.Fullreliefshowingacoarse-grainedcoatingwithouttheinternalpipe(notpreserved).&B.Transversesectionofthe
315 linedburrowwithcoarsening-centrifugaldistributionofskeletalfragments(fromfine-tocoarse-grainedsand)coatingtheinternalmuddy
316 pipe.&C.Meniscatestructurealignedalongthecentralaxisoftheburrowwhichisemphasizedbyweathering.&D–F.Imbricationisshown
bydistributionoftabular-shapedskeletalparticles(mainlyorbitolinids,well-sortedflatfragmentsofbivalveandgastropodshells,carbonate
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andsiliciclasticgrains).Grainsarealigneddefiningcurvedlaminae,whichareconcentricallyarrangedaroundtheaxiswithprogressively
318 increasinganglesfromtheinternalrodtowardstheouterpart,formingacharacteristic‘plumedstructure’.Notetheinternal(unstructured)
319 muddypipearrowedintheholotypeofFig.4D(EGSGT109).Paratypes(EGSGT110-T111-T112)areillustratedinFig.4A,C,F&G.
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321 fill preserved in convex hyporelief, as indicated by never cut each other, probably because of the early
322 Keighley & Pickerill (1994, pl. 1, fig. 6). Menisci cementation induced by biogenic mucus.
323 converge at the margins of a depressed U-shaped
324 region aligned parallel to the central axis, while the Morphological affinities. – Lined, cylindrical and hor-
325 coarsest grains are distributed laterally (Fig. 4C–G). izontal tubes of the Serra Gelada area show morpho-
326 The spreiten, marking the direction of locomotion logical affinities with several trace fossils, but reveal
327 of the burrower, are generally clearly visible in the also many differences, considering both the internal
328 outer bioclastic part, indicating that most burrowers imbricated structure of the shell-armoured tube and
329 had the same direction of locomotion. Crossing external shape. First of all, the framework (particle
330 trace fossils appear closely and tightly entwined and organization and related imbrication) suggests close
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LETHAIA 38(2005) Albian shell-armoured andassociated echinoidtrace fossils from Spain 7
331 affinities with the ichnospecies Diopatrichnus Gelada trace fossils is unlikely. In addition, informa-
332 roederensis Kern (1978) and Diopatrichnus odlingi tion concerning the arrangement of grains in the
333 de Gibert (2003), both known from their holotypes holotype of Lepidenteron is lacking.
334 only. In cross-section, the concentric distribution Imbrication,involvingtestsoflargeforaminiferans,
335 of particles is closely similar to the shell-lined tube is also present in tube-like trace fossils illustrated by
336 Diopatrichnus odlingi described by de Gibert (2003). Roniewicz (1970, fig. 9) and defined as Nummipera
337 Longitudinally, instead, the shape and peculiar eocenicabyHolder(1989,figs.2–9).Thelatterauthor
338 framework of the skeletal fragments differs from described a new ichnogenus and ichnospecies from
339 theholotypeofDiopatrichnusodlingideGibert(2003) the Eocene as a vertical tube-like trace fossil build
340 which does not show the characteristic imbricated of flat tests of large foraminifers (nummulitids).
341 structure(seeKern1978,fig.2;deGibert2003,fig.4). Somecharacteristicsconcernonlytheorganizationof
342 Moreover, our shell-armoured tube coats an skeletalparticles:theyareimbricatedandallgrainsare
343 inner, unstructured pipe made of silty sediment of the same size (e.g. discocyclinids) but do not
344 which is lacking in Diopatrichnus roederensis and, show the typical concentric, coarsening-centrifugal
345 probably, also in D. odlingi. Kern (1978) interpreted pattern, which is typical for the Serra Gelada trace
346 DiopatrichnusroederensisasthetubecapofaDiopatra fossils. Moreover, the internal rod is not present in
347 species, i.e. an onuphid worm building shell- Nummipera eocenica and the internal part is not a
348 armoured vertical burrows (Myers 1970, 1972). tubularmuddypipethatchangesinsize(Holder1989,
349 Attached particles are imbricated upwards also in fig. 2).
350 otherextanttube-buildingpolychaetessuchasOwenia The external shape, as discussed by Caracuel
351 (Fager 1964). The chimney-building worm Diopatra et al. (2002), also reveals some morphologic affinities
352 mayformaninvertedJ-bentburrowstickingoutfrom to Imbrichnus wattonensis, which is described from
353 1 to 6cm above the sediment surface whose tube the Forest Marble (Bathonian) in Dorset, England
354 termination is bent over so that the tube mouth (Hallam 1970, pl. 2b, c, text-fig. 2). Caracuel et al.
355 faces the sea-floor obliquely (Bromley 1996). In this (2002) emphasized the similarities with Imbrichnus
356 position, the tube cap is oriented normal to the main wattonensis with respect to the external morphology,
357 direction of current flow (Myers 1970). De Gibert which is meandering in shape and aligned more or
358 (2003) suggested a similar organism for terebelloid less parallel to the bedding (positive hyporelief).
359 wormtubesrecoveredfromtheMiddleJurassicWhite Probably, the meandering represents bivalve locomo-
360 Limestones of Oxfordshire, although the horizontal tion, included in Protovirgularia by Seilacher &
361 development of tubes is unsuitable for tube-building Seilacher (1994). The Dorset trace fossil shows a
362 polychaetes (Fager 1964; Myers 1972). De Gibert sediment-filling feature with a characteristic imbrica-
363 (2003)interpretedhorizontalDiopatratubestobethe tion (as indicated by the name) consisting of succes-
364 result of reworking by storm activity. According to sive pads of sandstone 1 to 3mm thick. However,
365 Myers (1970), the tube cap of Diopatra might be many differences exist in the imbrication style of the
366 horizontally oriented only if compressed during pads in Imbrichnus, which seems to be a superficial
367 sediment compaction after final burial (see type I (external) structure (Hallam 1970). Imbrication of I.
368 of Myers 1970, fig.1b). Therefore, the ichnogenus wattonensis develops as V-shaped folds only in the
369 Diopatrichnus should be employed exclusively for horizontal plane (folds inclined at 60(cid:1) or less com-
370 vertical burrows and thus is not appropriate for pared to the axis), not affecting the whole coating as
371 the horizontally structured tubes from the Serra observed in the Serra Gelada material. Moreover, the
372 Gelada area. internal muddy pipe of the latter is lacking in the
373 The horizontal tube-like trace fossil Lepidenteron, traces from the Forest Marble and the grains do not
374 which may be referred to the activity of terebelloid reach the coarse sand or pebble size observed in the
375 worms, has been redescribed by Suhr (1988) and specimens from Spain. Thus, the grain arrangement
376 this author indicated four ichnospecies based on and the framework of the coated tubes are totally
377 the construction material of the tube (fish remains, different in these two cases.
378 needles of coniferes, mucous particles and a lot Grainalignmentintheexternalcoatingshowssome
379 of various grains) which the worm had used. analogies to the arcuate meniscate fill preserved in
380 The thickness and length (up to 35mm and convex hyporelief of Taenidium barretti (Bradshaw),
381 20cm, respectively) and horizontal development of which is illustrated and discussed by Keighley &
382 Lepidenteron variabilis (Suhr 1988, fig. 3) are con- Pickerill(1994).Nevertheless,menisciareeachshaped
383 sistentwiththeSpanishtracefossils,butorganization like a crescent moon in Taenidium barretti and are
384 of the various grains are very poorly imbricated in clearly developed in the entire burrow; they converge
385 Lepidenteron and suggests that affinity with the Serra at the margins of the structure forming cusps and
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386 givingthegeneralappearanceofacrescenticmeniscate (spatangoids) are preserved within their burrows or
387 segment (Keighley & Pickerill 1994). In the Serra concentrated at the end of trace fossils (Fig. 5B–C,
388 Gelada material, menisci are seldom preserved arrow). Echinoid tests are very abundant in the
389 (Fig.3C,seearrow)andtheconvergenceisnotclearly lower –middle parts of the section (Fig. 2, Holaster
390 visible at the margins, probably due to the nature intermedius,Epiastersp.,Epiasterdalloni,Toxastersp.,
391 of the coarse-grained material. Locally, menisci are Toxasteramplus,Discoidesconica,Nucleitessp.)where
392 concentrated in a couple of internal bands aligned well-preserved tests are scattered or concentrated
393 mainly along the central axis of the burrow and are (Fig. 5E). In any case the distribution of echinoids
394 moreeasilyvisiblebecauseofweathering(Fig.4C–G). coincides with the abundance of grain-coated
395 For a detailed description of Taenidium and its affin- trace fossils and indicates that spatangoid echinoids
396 ities with other ichnogenera such as Beaconites and perished very close to their burrows (Fig. 5A, B–C).
397 Ancorichnus we refer to Keighley & Pickerill (1994). Locally, convex resting impressions, ovoid in
398 The shell-armoured burrows of the Serra Gelada outline, are preserved at the end of the slightly
399 section show an inner, unstructured horizontal pipe meandering echinoid burrows (Cardioichnus, see
400 represented by fine-grained, peloidal grey silty mud Fig. 6A, B).
401 (Fig.4D).Thissiltypipediffersfromtheinternalrod,
402 which is named Bichordites (Plaziat & Mahmoudi Morphological affinities. – A close relationship exists
403 1988), since no cordate or lozenged-shaped section is between the grain-coated trace fossils of the Serra
404 revealedincross-section,asreportedbytheseauthors. Geladaareaandthehorizontalonesformedmainlyby
405 The meniscate pattern of Bichordites is not present spatangoids(seeFig.2).Forirregularechinoidsofthe
406 in the Serra Gelada trace fossils, where the pipe is order Spatangoida, burrowing is considered the rule
407 completely unstructured and their external surface (Bromley & Asgaard 1975; Smith & Crimes 1983;
408 retracesthesmoothliningmadebythecoarse-grained Uchman 1995; 1998; Kanazawa 1995; Lebrun 2000).
409 material. Therefore, it is possible that the internal The excavation activity of lateroventral spines of the
410 pipe represents an infill of faecal products by the echinoid results in forward movement and redeposi-
411 same organism, which produced the shell-armoured tion of grains in sandy sediment, while it does not
412 coating tube. work well in muddy sediments, which are too soft
413 andcohesive forexcavation andtransport(Kanazawa
414 1995). Grain alignment does not generally show
(2) Non-imbricated, grain-coated trace fossils
415 sorting or imbrication, but flat grains are con-
(unstructured)
416 centrically disposed around the axis of the trace, as
417 Description. – These horizontal burrows consist of observed in Echinocardium cordatum (Kanazawa
418 an inner muddy pipe, which is coated by a coarse- 1995) and in the Serra Gelada trace fossils (Fig. 5C,
419 grained tube. The tube – and in contrast to the shell- white arrow). As far as lithification of Echinocardium
420 armoured trace fossils described above – is without cordatum traces is concerned, Bromley & Asgaard
421 any well-defined framework of particles, where the (1975) noted that the lower halves of burrows are
422 coarse-grained grains are casually distributed and not preferentially lithified in contrast to the upper ones
423 imbricated.Atransversesectionoftheburrowsreveals duetomucussecretedattheambitus(Pe´quignat1970;
424 apeculiarstructureintheinternalmuddypipe,which Kanazawa 1995). Thus, the grain-coated trace fossils
425 showstwolaterallobesandacentralV-shapedregion from Serra Gelada can be attributed to spatangoid
426 (Fig. 5D). The internal pipe changes in size, reaching activities since only the lower halves of their burrows
427 upto4–5cmindiameter,inoneandthesameburrow are preserved (Fig. 5B, D–F).
428 (Fig. 5F). Concerning the preservation of the coating, The external shape and cross-section of Sub-
429 the lower half of the burrow is preferentially lithified phyllochordaandCardioichnus[illustratedbySmith&
430 in contrast to the upper half where it is lacking Crimes (1983, figs. 3–5,7)] and Scolicia (i.e. Uchman
431 (Fig. 5B–F). Coating is often reddish and shows a 1998, fig. 60) show close analogies to the Serra
432 slightly coarser-grained texture in respect to the Gelada non-imbricated, grain-coated trace fossils.
433 neighbouring dark grey and finer sediment, envelop- Subphyllochordaconsistsofmeanderingridgesusually
434 ing a pipe, which resembles a monk’s cowl (Fig. 5A). bilaterally symmetrical and convex in shape (Smith
435 The unstructured coating tube generally consists of & Crimes 1983). As reported by those authors,
436 small bioclasts or detrital sandy grains mixed with the trace in cross-section is ovoid in outline and
437 finer sediment, probably cemented during early concentric lamination can be observed in polished
438 diagenesis. The boundary between the coating and or etched sections (Smith & Crimes 1983; Uchman
439 the pipe is sharp and clearly visible in cross- 1998, fig. 60). Although Smith & Crimes (1983)
440 section (Fig. 5C). In some samples echinoid tests described two separate ichnogenera (Subphyllochorda
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LETHAIA 38(2005) Albian shell-armoured andassociated echinoidtrace fossils from Spain 9
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473 Fig. 5. Grain-coated trace fossils (non-imbricated) referred to the ichnogenera Scolicia and Cardioichnus, and echinoid-rich levels, Serra
474 Gelada section (Albian, Lower Cretaceous), Alicante area, southeast Spain. &A. Unstructured, coarse-grained burrow, which envelops a
muddysediment.&B.Lowerhalvesofburrowsarepreferentiallylithifiedincontrasttotheupperonesthataredestroyed(seealsoFig.5D–F).
475 Echinoidtests(spatangoids)areseldompreservedwithintheirburrows(seearrow).&C.Theboundarybetweencoatingandpipeissharpand
476 clearlyvisibleintransversesections.&D–F.TheinternalmuddypipeshowstwolaterallobesandacentralV-shapedregion;thechangesinsize
477 in a same burrow reach up to 4–5cm in diameter. &E. Echinoid-rich level in which, compaction and collapse of echinoid tests are
characteristicbiostratinomicfeatures.HammerheadforscaleinFig.5A,B,D&F.
478
479
480 and Scolicia), Uchman (1995, 1998) included (Kanazawa 1995). Well-defined laminae (2–4mm)
481 Subphyllochorda and other similar taxa, such as of the lateral mantle are arranged in two alternating
482 Taphrhelminthopsis,LaminitesandTaphrhelminthoida series along a central zone, which is also laminated
483 within Scolicia as taphonomic variants of the same (floor according to Smith & Crimes 1983). Scolicia is
484 ichnogenus produced by heart-shaped sea-urchins. commonly developed in medium to fine-grained
485 Uchman (1995, 1998) pointed out that Sub- sandstone beds, few centimetres below the top of
486 phyllochorda-like specimens, which do not show turbidite-hemipelagitebedandpreservedinfullreliefs
487 peculiar features (such as clear division of the main (Uchman 1995, 1998).
488 ridge), cannot properly be distinguished as different In the Serra Gelada material the echinoid burrow-
489 ichnogenera.ThusUchman(1998)proposedtopolish ing activity is concentrated close to the sand/mud
490 the Subphyllochorda-like specimens at the lowermost interface without producing double sanitary tubes
491 part in order to expose the structure of medial lobe (2–5mm in diameter, ovoid in cross-section and
492 for a proper identification. Scolicia is a bilobate or cohesive; see Smith & Crimes 1983). This double
493 trilobate back-filled echinoid trace fossil (usually sanitarytubeisseldomvisibleintheSerraGeladatrace
494 meandering)withtwoparallelsedimentstrings,which fossils. Only two cases have been recognized in the
495 represent the drainage canals of spatangoid echinoids Serra Gelada section. The paucity of two parallel
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10 P. Monaco etal. LETHAIA 38(2005)
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523 Fig.6.Grain-coatedtracefossils(non-imbricated)attributabletohearturchins(Cardioichnusisp.),(Albian,LowerCretaceous),SerraGelada
section,Alicantearea,southeastSpain.&A–B.Convexrestingimpressions,ovoidinoutline,preservedattheendoftheslightlymeandering
524
echinoidburrow(Cardioichnusisp.,seearrows).Hammerforscale.&C.HorizontalmazesofY-shapedThalassinoidesisp.;thelowersurface
525 ofbedisupsidedown.Hammerforscale.&D.Topofacoarse-grainedcalcarenitebedwithatracefossilassemblageofOphiomorphaisp.
526 FromthelowerpartoftheSerraGeladasection.
527
528
529 strings of fine sediment produced by the heart trace fossils collected from the Serra Gelada section
530 urchin may be explained, firstly, by the poor (Figs 5–6).
531 preservation of the lower halves of the burrows, and
532 secondly, by the development of diagenetic features
533 affectingthecoarsegrainsizeofinvolvedsandy/pebbly Discussion and conclusions
534 particles.
535 Cardioichnus is a convex resting impression, ovoid Two varieties of Ereipichnus geladensis may be
536 in shape and also bilaterally symmetrical, showing distinguished: type 1 is rectilinear in shape and uni-
537 two wide lateral lobes, anteriorly linked and with a directional (most of the burrows are N–S oriented
538 depressed V-shaped region towards its posterior both for each bed and along the whole section),
539 part. In the description by Smith & Crimes (1983), and type 2 is curved and slightly meandering in the
540 Cardioichnus and Subphyllochorda are frequently horizontal plane (Fig. 3C, D and A, B, respectively).
541 associated in continuity, the first one generated Both varieties are segregated at different stratigraphic
542 when the echinoid temporarily stops and slightly intervals: type1 is present in the middle part of the
543 changes its vertical locomotion for temporary refuge, Serra Gelada section, while type 2 has been found at
544 forming the characteristic Cardioichnus convex the top of the section. Their abundance is controlled
545 shape (Smith & Crimes 1983, fig. 9). This relation- by lithology. Rectilinear, tightly packed tubes of
546 ship between Cardioichnus and Subphyllochorda- Ereipichnusgeladensistype1dominateinfine-grained,
547 like specimens is recognized in echinoid-rich levels marly beds where the density of jutting tubes is
548 in the Serra Gelada specimens (Fig. 6A–B, arrow). high,reachinginsomebeds400specimens/m2.These
549 The holotype of Cardioichnus planus (Smith & jutting burrows are similar to terebelloid tubes
550 Crimes 1983, fig. 7c) is similar to the grain-coated cited for the Serra Gelada area by Moseley (1990).
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