The trace fossil Asthenopodichnium lithuanicum isp. nov. from Late Neogene brown-coal deposits, Lithuania

The trace fos sil Asthenopodichnium lithuanicum isp. nov. from Late Neo gene brown-coal de pos its, Lith u a nia

Al fred UCHMAN, Algirdas GAIGALAS, Monika MELEŠYT# and Vaidotas KAZAKAUSKAS

Uchman A., Gaigalas A., MelešytÅ M. and Kazakauskas V. (2007) — The trace fos sil Asthenopodichnium lithuanicum isp. nov. from Late Neo gene brown-coal de pos its, Lith u a nia. Geol. Quart., 51 (3): 329–336. Warszawa.

A new fresh wa ter ichnospecies of Asthenopodichnium Thenius, A. lithuanicum, is dis tin guished by its pouch-like shape with a J-shaped limb that is dis tinctly wider than the re main ing part of the pouch. It was pro duced in a stiffground at the top of a min eral-rich brown-coal layer of Neo gene age by a sus pen sion feeder form ing pouch-like domichnial cav i ties. May fly lar vae may per haps be con sid ered as can di - dates for its tracemaker. Other ar thro pods (am phi pods, isopods) are also pos si bil i ties. The brown-coal layer was ex posed dur ing the Neo - gene by river ero sion, was col o nized by the tracemaker (lo cally two col o ni za tion events took place) and in the Plio cene cov ered by dis tal cre vasse and river chan nel sands.

Al fred Uchman, In sti tute of Geo log i cal Sci ences, Jagiellonian Uni ver sity, ul. Oleandry 2a, PL-30-063 Kraków, Po land, e-mail:

fred@geos.ing.uj.edu.pl; Algirdas Gaigalas, Monika MelešytÅ, De part ment of Ge ol ogy and Min er al ogy, Vilnius Uni ver sity, Èiurlionio, 21/27, LT-03101 Vilnius, Lith u a nia, e-mail: Algirdas.Gaigalas@gf.vu.lt; Vaidotas Kazakauskas, De part ment of Qua ter nary Ge ol ogy, In sti tute of Ge ol ogy and Ge og ra phy, T. Ševèenkos str. 13, LT-03223, Vilnius, Lith u a nia, e-mail: kazakauskas@geo.lt (re ceived: Jan u ary 22, 2007; ac cepted: June 24, 2007).

Key words: Lith u a nia, Neo gene, ichnology, tax on omy, brown coal, stiffground.

INTRODUCTION

Or ganic-rich de pos its such as coal, lig nite, wood (xylite) or gyttja are rarely a sub strate for bur row ing or bor ing or gan isms in aquatic en vi ron ments, the ac tion of which is re corded as trace fos sils. Literature on this topic is very scarce. Philipp and Wehrli (1936) and Schenk (1937) de scribed bor ings of ma rine bi valves (Teredolites) in lig nites from Neo gene brown-coal de - pos its in Ger many. Sim i larly, Bromley et al. (1984) de scribed the ma rine wood bor ing Teredolites clavatus Leymerie from the top sur face of a coal layer in the Late Cre ta ceous Horse shoe For ma tion, Al berta, Can ada. More data con cerns bi valve bor - ings in wood in ma rine en vi ron ments. These are as cribed to the ichnogenus Teredolites (e.g., Kelly and Bromley, 1984; Savrda et al., 1993). Less well known are ma rine bor ings in wood pro - duced by am phi pods (Limnoria) and isopod crus ta ceans (Bromley, 1970, p. 66, and ref er ences therein) or other or gan - isms (Bann et al., 2005). To our knowl edge trace fos sils in brown coal or gyttja in non-ma rine aquatic en vi ron ments have not been re ported un til now. Very lit tle is known about bor ings in wood in fresh wa ters. Thenius (1979) de scribed the

ichnogenus and ichnospecies Asthenopodichnium xylobiontum from Late Neo gene wood in Aus tria and re ferred it to bor ings of may fly lar vae.

Some pouch-like trace fos sils have been dis cov ered at the top of a min eral-rich brown-coal layer in Neo gene brown-coal bog-lake and flu vial de pos its at Anykšèiai, North east ern Lith u - a nia (Fig. 1). Given the scar city of in for ma tion on bur rows and bor ings in fresh wa ter en vi ron ments in or ganic-rich de pos its, they are in ter est ing and po ten tially in crease our knowl edge on this topic. Their de scrip tion and in ter pre ta tion are the main aim of this pa per. Some of thse de posit il lus trated are housed in the In sti tute of Geo log i cal Sci ences of the Jagiellonian Uni ver sity (col lec tion pre fix 198P).

GEOLOGICAL SETTING

Neo gene de pos its, oc cur ring in iso lated patches in the val -

leys of the Šventoji River and its trib u tar ies, North east ern Lith u -

a nia, were dis cov ered by Dalinkevièius (1933), who as cribed

them to a Ter tiary brown-coal for ma tion (see also Dalinkevièius,

1960). Their micoflora and palaeocarpology were in ves ti gated

by VienožinskienÅ (1960), KondratienÅ (1971), RiškienÅ (1971) and Khomutova in Vaitiekñnas and Khomutova (1972). The lower part of the Lith u a nian Neo gene con tains mainly bog-lake fa cies and is as cribed to the Mio cene, whereas the up per, more widely dis trib uted flu vial part — to the Mid dle and Up per Plio - cene (Vaitiekñnas, 1977). The Plio cene de pos its at Daumantai in the Šventoji River val ley were dis tin guished as in ter me di ate be - tween the Neo gene and the Pleis to cene, and were re lated to (Gaigalas, 1987) the Anykšèiai Re gional Stage sensu KondratienÅ (1971). Baltakis (1966) and Katinas (1971, 1994) stud ied the Neo gene of Lith u a nia and of the Semba pen in sula.

For gen eral in for ma tion on the Lith u a nian Neo gene see also Paškevièius (1994, 1997).

THE LOCALITY STUDIED

The Neo gene brown-coal unit in ves ti gated crops out 2 km SW of Anykšèiai on the north ern side of the main road to Kovarskas–UkmergÅ (Fig. 1) in a sand pit, in which a very clean, white glass sand is ex ploited. The de pos its stud ied be - long to the East Lith u a nian fa cies area of the Neo gene and can be as cribed to the Plio cene. The sand is 4.5 to 6 m thick, fine-grained, cross-lam i nated (Fig. 2A) and cov ered with Pleis to cene boul der clays (tills) of the Mid dle Lith u a nian

phase of the Bal tic Stadial of Nemunas Gla ci ation. The Pleis - to cene rests on an ero sive exarational dis con ti nu ity. Un der the sands, a se quence of less clean, very fine- to me dium-grained sands about 2 m thick crop out (Fig. 2B) in the west ern part of the sand pit. These are in ter ca lated with ir reg u lar lay ers of brown coal and drapes of mudstone and siltstone. The lat ter form a heterolithic sed i ment. Be low, the top of the Up per De - vo nian red beds (Šventoji For ma tion) can be seen in ditches at the bot tom of the quarry.

The trace fos sils were found at the top of the high est brown-coal layer (Figs. 2C and 3), which is up to 9 cm thick and pinches out to the east. The brown-coal is com posed of black or black to dark brown de tri tal, mas sive or in dis tinctly lam i nated black or ganic mat ter, some min eral grains, in clud ing mica flake, quartz grains, clay min er als or cal cite, well-pre - served pieces of wood up to 7 cm long, and flat marcasite con - cre tions, 3–5 mm across, ly ing along the lamine. Mac ro scop i - cally, the coal re sem bles a min eral-rich coal sensu Tay lor et al.

(1998). Paškevièius (1997) showed that this is a clarain coal of the fri a ble attritus, heliolithic class. It dis plays a weakly coalified, fragmental and attritic microstructure, and is com - posed of tiny heliolitithified stems of bushes and her ba ceous plants, and frag ments of leaves, wood and bark. A leaf ma trix com posed of attritus dom i nates. Lat er ally, the brown-coal lay - ers are re placed by coaly sand, silt and clay.

Fig. 1. Lo ca tion maps and a gen eral sec tion of the sand pit at the lo cal ity stud ied;

the de tailed map is with out Qua ter nary de pos its (based on the Geo log i cal Map 1: 200 000 by Šliaupa et al., 2000)

A — lo ca tion of stud ied area in Lithuania; B — lo ca tion of the stud ied sec tion; C — lithostratigraphic col umn of the stud ied sec tion and lo ca tion of the trace fos sil bear ing horizon

The veg e ta tion was of a sub trop i cal type grow ing on a large al lu vial plain. The re mains of veg e ta tion were trans ported by streams and de pos ited as allochthonous de tri tus in ox bow lakes as a peaty gyttja or coal. The Plio cene veg e ta tion shows a cli - ma tic cool ing in com par i son to the Mio cene. Among the spores and pol len Pinus silvestris pre vails, comparising up to 70%

(10–50% in the Mio cene) while the Taxodiaceae de creased to 5% from 45% in the Mio cene. Thermophilous plants are rare, but Quercus, Corylus and Carpinus are fre quent. Betula and Alnus pre vailed among the bo real tree spe cies.

From a dis tance the trace fos sils are vis i ble as white sand-filled spots, a few mm wide against the dark back ground of the brown coal. An additional trace fos sil (form A) was found in the pieces of wood that oc cur in the brown-coal lay ers.

Prob a bly, the cross-bed ded sands above the brown-coal lay ers were de pos ited in bars of a sandy braided river. The sands in the brown-coal unit orig i nated prob a bly in a me an - der ing or anostomosing river with in a flu vial plain with ox - bow lakes or aban doned chan nels. There is no ev i dences of ma rine in flu ence.

TRACE FOSSILS

Ichnogenus Asthenopodichnium Thenius 1979 Type ichnospecies Asthenopodichnium xylobiontum

Thenius 1979

E m e n d e d d i a g n o s i s. — Small, U-shaped spreiten or pouch-like struc tures in wooden, or ganic-rich or bone sub strates.

R e m a r k s. — Ma te rial of the type ichnospecies of Asthenopodichnium, A. xylobiontum dis tin guished by Thenius (1979), was dis cov ered in the Late Mio cene (Pannonian) de - pos its of the Vi enna Ba sin (Papp, 1949; Papp and Thenius, 1954; Thenius, 1979). Orig i nally, the ichnogenus Asthenopodichnium was di ag nosed by Thenius (1979) as

“U-shaped spreiten bur rows in wood, ver ti cally ori ented to the

Fig. 2. The lo cal ity stud ied in pho to graphs

A — view of the quarry; B — view of the brown-coal de pos its with the gyttja layer bear ing trace fos sils; C — Asthenopodichnium lithuanicum at the top of the coal layer

Fig. 3. De tailed sec tion of the Anykšèiai brown-coal de pos its with the trace fos sils

up per side the log”. The spreiten, how ever, are not ob vi ous be - cause even in the type ma te rial, the trace fos sil ap pears as a tongue filled with other, non-xylic ma te rial and prob a bly is a cast of a spreiten trace fos sil, in which limbs and pos si ble spreiten formed a sin gle cav ity be fore cast ing. More over, its oc cur rence in brown coal and even in or ganic-rich siltstone en - larges its sub strate con straints. For these rea sons the di ag no sis has been emended.

Bertling et al. (2006) con sid ered the ma jor sub strate types as ichnotaxobases. In the case of the new, third ichnospecies of Asthenopodichnium de scribed in this pa per, the bound ary be - tween the sub strate types is not sharp be cause of its oc cur rence in the or ganic-rich silt. This, how ever, can be con sid ered as an ex cep tion, which does not af fect the gen eral rule.

Hith erto, only two ichnospecies of Asthenopodichnium Thenius 1979 have been rec og nized. A. xylobiontum Thenius 1979 was di ag nosed as “U-shaped spreiten with limbs 1.5–3 mm in di am e ter and depth (height) up to 20 mm”. A.

ossibiontum Thenius 1988, rec og nized in mam mal bones from the Neo gene of the Vi enna Ba sin, Aus tria, is di ag nosed sim i -

larly. Thenius (1988) em pha sized that its dif fer ence from A.

xylobiontum is based mostly on bi o log i cal pref er ences of the tracemaker (wood ver sus bones), though some morphometric dif fer ences can also be seen (Figs. 4 and 5).

In gen eral, the bar na cle bor ings Rogerella Saint-Seine (1951) and Zapfella Saint-Seine (1956) are sim i lar to Asthenopodichnium in their over all shape, but these two ichnogenera are found only in lithic ma rine sub strates, pri mar - ily in cal car e ous skel e tons (e.g., Bromley, 1970; Häntzschel, 1975). Diplocraterion luniforme (Blackenhorn 1916) from the Cre ta ceous flu vial clastic Hasandong For ma tion, Ko rea (Kim and Paik, 1997) dis plays a sim i lar size and over all shape, but it dis plays U-shaped limbs and spreiten.

Asthenopodichnium lithuanicum isp. nov.

(Figs. 2C, 4 and 6)

M a t e r i a l a n d h o l o t y p e. — 10 small slabs (198P1-5; 198P7-11) with more than 50 trace fos sils al to gether.

The holotype is on the slab 198P1. It is shown in Fig ure 6A. All the re main ing spec i mens in the slab are co-types.

D i a g n o s i s. — Pouch-like struc tures in brown coal and rarely in or ganic-rich siltstones, which dis play a J-shaped limb that is dis tinctly wider than the other part of the pouch.

D e s c r i p t i o n. — Small, sand-filled tongues at the top of a brown-coal layer or in pieces of wood. They are ori ented ver ti cally at the top of the brown coal. The hor i zon tal cross-sec - tion (Fig. 6A) shows that the bur row dis plays a dis tinct limb on only one side. Thus, it is a J-shaped rather than U-shaped struc - ture. The limb is dis tinctly wider than the re main ing part of the pouch. The pouches are 4–7.5 mm wide, from 1.5 to 4 mm thick in the limb (Fig. 5), and up to 7.5 mm high (deep). They are scat tered on the sur face of the brown-coal layer with out any pre ferred ori en ta tion but they tend to oc cur in clus ters. In di vid - ual bur rows are 1–5 mm apart in a clus ter. The clus ters are lo - cated 15–25 mm apart. In di vid ual bur rows are rare.

A. lithuanicum oc curs in the 2 cm-thick top part of the layer (Figs. 2C, 6B–C). Its top com prises the bound ary be tween the brown coal and the over ly ing sand or a lamina sur face lo cated about 10 mm be low the bound ary (Fig. 6C). The bound ary and lamina sur faces are in ter preted as two col o ni za tion sur faces.

R e m a r k s. — The trace fos sil de scribed fits best the ichnogenus Asthenopodichnium be cause of its over all shape and oc cur rence in non-lithic sub strates. It dif fers from A.

xylobiontum and A. ossibiontum in the dis tinct J-shaped limb that is wider than the re main ing part of the pouch (Fig. 4).

Form A (Fig. 7A)

M a t e r i a l. — A xylite (198P6) from the brown-coal layer with a few bor ings.

D e s c r i p t i o n. — Elon gate oval de pres sions in the sur face of a wood frag ment. The de pres sions are 8.5–11 mm

Fig. 4. Mor pho log i cal mod els of Asthenopodichnium ichnospecies

[ ]

[ ]

Fig. 5. Thick ness and width of Asthenopodichnium ichnospecies pouches, form A and lebensspuren dis cussed in the pa per

long, 1.8–2 mm wide, and up to 2 mm deep. They are ori ented par al lel or sub-par al lel to the wood grains.

R e m a r k s. — The de pres sions re sem ble Asthenopo - dichnium xylobiontum Thenius 1979 in their size (Fig. 5) and out line. How ever, the lat ter trace fos sil is deeper. How ever, it is not ex cluded that it is a bot tom part of A. xylobiontum that re - mained af ter ero sion of the sur face part of the wood.

DISCUSSION

The two ichnospecies of Asthenopodichnium, A.

xylobiontum and A. ossibiontum, are bor ings in a hard sub strate.

A. lithuanicum is a bur row be cause it oc curs in the brown coal and there is no ev i dence that the grains are cut by the tracemaker.

Fig. 7. Form A and lebensspuren re lated to Asthenopodichnium

A — form A in the sur face of a piece of wood, 198P6; B — lebensspuren type B in the form of elon gate de pres sions in the sur face of Pleis to - cene gyttja ex posed in the bot tom of the Neris River chan nel, NW of Vilnius, 198P13; C — lebensspuren type C in the form of pouche de pres - sions in the sur face of Pleis to cene gyttja, 198P12, the same lo ca tion as in B

Fig. 6. Asthenopodichnium lithuanicum isp. nov.

A — slab 198P1 with the holotype (H); B — slightly de formed A. lithuanicum at the top of the coal layer; C — two col o ni za tion sur faces (1 and 2) at the top of the coal layer; field pho to graphs in B and C

More over, some of the bur rows are slightly compactionally de - formed (Fig. 6B) show ing the sub strate was still plas tic. The oc - cur rence of bur rows and bor ings within an ichnogenus is not sur - pris ing. There are even stranger ex am ples, such as Gastrochaenolites oelandicus from the Or do vi cian of Swe den, which is known both as bor ings and bur rows within the same ichnospecies (Ekdale and Bromley, 2001).

Trace maker iden ti fi ca tion is an in trigu ing prob lem as re - gards A. lithuanicum. Thenius (1979) on the ba sis of lit er a ture and of re cent ma te rial, re ferred Asthenopodichnium xylobiontum to traces of may flies of the fam ily Polymitarcidae = Ephoronidae (e.g., Tortopus, Asthenopus, Povilla) pro duced in wood of re cent lakes and rivers of Paleotropis, Neotropis and the SE USA. Thenius (1979) in - cluded within A. xylobiontum elon gate de pres sions pre served in a xylite in Late Ter tiary brown coal in NW Ger many on the ba sis of ma te rial il lus trated by Schenk (1937, fig. 6; also Thenius, 1979, pl. 1, fig. 1). Re cent de pres sions of this type have been found in the bot tom of chan nel of the Neris River (Vilija), NE of Vilnius, Lith u a nia (lebensspuren type B;

Fig. 7B). The de pres sions are 9–11 mm long, up to 2 mm wide and up to 2 mm, ex cep tion ally 4 mm deep. They occure on the sur face of a Pleis to cene inter gla cial gyttja (160–180 ka). More - over, such de pres sions have been found in pieces of wood from the Vistula River near War saw, Po land (M. Paszkowski, pers.

comm.). The sur face of the gyttja NW of Vilnius con tains also larger de pres sions (lebensspuren type C; Fig. 7C) with ar cu ate bot toms, which are 11–12 mm long, 4–5 mm wide, and up to 10 mm deep. All of these can be as cribed to Asthenopodichnium-like bur rows (in gyttja) or bor ings (in wood). This ex cludes may flies of the fam ily Polymitarcidae, which do not now oc cur in Eu rope, ex cept for Ephoron virgo (Ol i ver). E. virgo, how ever, pro duces larger and deeper bur - rows with dis tinct U-shaped limbs (Abel, 1935, fig. 370), up to 80 mm deep (e.g., Stief et al., 2004). Other Eur asian may fly lar vae pro duce dis tinctly larger and deeper U-shaped bur rows (e.g., Russev, 1987; De, 2002). The same ob ser va tions con cern trace fos sils at trib uted to may flies (Storch, 1926; Fürsich and Mayr, 1981). There fore, in ter pre ta tions of pouch-like trace fos - sils and lebensspuren ex clu sively as traces of may fly lar vae can be chal lenged. Un for tu nately, an al ter na tive, con vinc ing in ter - pre ta tion can not be pro posed. Pem ber ton and MacEachern (1992, p. 56) and Pem ber ton et al. (1992, p. 18A; 2001, p. 81, 195) men tioned shal low, “sparse to pro fuse nonclavate etch - ings” pro duced by isopod crus ta ceans in a fresh wa ter wood sub strate, but more de tailed char ac ter is tics were not pro vided.

Hoffmann and Hering (2000) dis tin guished fac ul ta tive xylophagous taxa among fresh wa ter Gastropoda, Trichoptera, Isopoda, Coleoptera, and ob li gate xylophagous an i mals among fresh wa ter Diptera, Trichoptra and Coleoptera. Their

lebensspuren, how ever, are un known. The ge om e try and lo ca - tion in the sec tion sug gest that the tracemaker A. lithuanicum was prob a bly a sus pen sion feeder form ing domichnial pouch-like de pres sions as shel ters.

A. lithuanicum was formed at the top of peaty gyttja layer (now the brown coal), which prob a bly formed in an ox bow lake. The peaty gyttja was prob a bly ex posed by a cre vasse ini ti - at ing the cut ting of a new chan nel in a flu vial plain and en ter ing the ox bow lake. The ex posed layer was prob a bly stiff (a stiffground sensu Wetzel and Uchman, 1998) as in di cated by well-out lined trace fos sils, which are only lo cally slightly com - pacted. At least two col o ni za tion sur faces can be seen (Fig. 6C) in places when the coal is thick est. Prob a bly, af ter the first col o - ni za tion, the bur rows were filled pas sively with sand of a dis tal cre vasse. Later, on a thin, about 1 cm-thick layer of peaty gyttja ac cu mu lated. Af ter col o ni za tion of this thin layer, cre vasse and river chan nel sed i ments ac cu mu lated and filled the bur rows.

Asthenopodichnium lithuanicum and re lated forms have been found only in brown coal, gyttja or wood. This sug gests that this trace fos sil is a sub strate-spe cific form. Its in ter pre ta - tion as a sus pen sion feeder domichnion, how ever, makes dif fi - cul ties in explaining how the tracemaker ben e fits from the coaly or woody sub strate. In com par i son to clastic stiff sub - strates, brown coal or woody sub strates are softer and their ther mal con duc tiv ity is higher. There fore, pro duc tion of cav i - ties can be eas ier in brown coal or wood. More over, they give more pro tec tion against changes of tem per a ture in a flu vial en - vi ron ment, which can be important for life of the tracemaker.

CONCLUSIONS

1. Asthenopodichnium lithuanicum from brown-coal de - pos its of Neo gene age in Lith u a nia is a new ichnospecies dis - tin guished by its pouch-shape with a J-shaped limb that is dis - tinctly wider than the re main ing part of the limb.

2. A. lithuanicum oc curs at the top of a brown coal layer that was ex posed by river ac tion dur ing the Plio cene and was formed in a stiffground.

3. A. lithuanicum was pro duced by a sus pen sion feeder form - ing pouch-like domichnial cav i ties. May fly lar vae may per haps be con sid ered as can di dates for its tracemaker. Other ar thro pods (am phi pods, isopods) are also possibilities.

Ac knowl edge ments. Al fred Uchman was sup ported by the

Jagiellonian Uni ver sity (BW funds) and the Lith u a nian State

Sci ence and Study Foun da tion. The pa per bene fited from re -

view by Grzegorz Pieñkowski (War saw) and fur ther im prove -

ments pro posed by Marek Narkiewicz (War saw).

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