Large cruzianid trace fos sils in the Or do vi cian of the peri-Bal tic area:
the case of the Bukówka For ma tion (Holy Cross Moun tains, Po land)
Micha³ STACHACZ1, *, Weronika £ASKA1 and Al fred UCHMAN1
1 Jagiellonian Uni ver sity, In sti tute of Geo log i cal Sci ences, Gronostajowa 3a, 30-387 Kraków, Po land
Stachacz, M., £aska, W., Uchman, A., 2018. Large cruzianid trace fos sils in the Or do vi cian of the peri-Bal tic area: the case of the Bukówka For ma tion (Holy Cross Moun tains, Po land). Geo log i cal Quar terly, 62 (2): 400–414, doi: 10.7306/gq.1412 The Mid dle Or do vi cian Bukówka For ma tion, com posed of fine-grained quartz sand stones with siltstone in ter ca la tions, be - longs to the Kielce Re gion of the Holy Cross Moun tains (peri-Bal tic palaeogeographic po si tion). It con tains trace fos sils of low di ver sity and poor pres er va tion. Par tic u larly note wor thy are the large Cruziana and Rusophycus, that are typ i cal of peri-Gondwanan ar eas. They con sist of casts of bilobate fur rows show ing di verse pres er va tion. Other trace fos sils in clude mostly hor i zon tal pascichnia, cubichnia, and fodinichnia, but also ver ti cal domichnia. The trace fos sil as sem blage is typ i cal of the ar che typal Cruziana and partly of the Skolithos ichnofacies. Some beds con tain abun dant orthid brachi o pods. The trace fos sils and sed i men tary struc tures (hor i zon tal, low-an gle and wave rip ple cross-lami na tions, hummocky cross-strat i fi - ca tion) sug gest de po si tion on the mid dle and lower shoreface with storm in flu ence. The poor pres er va tion and low di ver sity of the trace fos sils are re lated to the ho mog e neous li thol ogy, low ac cu mu la tion rate, shal low burial of or ganic mat ter and strong bioturbation. There fore, an i mals bur rowed strongly but mostly in shal low tiers. Thus, the pres er va tion po ten tial of their traces was much lower than in many peri-Gondwanan sec tions but still higher than in Baltica sed i men tary rocks. This ex - plains the pro vin cial dif fer ences in ichnofauna dur ing the Or do vi cian, which at least partly were in flu enced by the pres er va - tion po ten tial.
Key words: Or do vi cian, trace fos sils, bioturbation, Cruziana, taphonomy, Baltica.
INTRODUCTION
Lower Pa leo zoic trace fos sils show some pro vin cial spec i - fic ity (e.g., Seilacher, 1992, 2007; Servais et al., 2010). For in - stance, those from the Or do vi cian Sys tem of Gond wana (e.g., ïOrbigny, 1842; Rouault, 1850; Lebesconte, 1883, 1886;
Delgado, 1886; Seilacher, 1970; Baldwin, 1977a; Durand, 1984, 1985a, b; Neto de Carvalho, 2006) are char ac ter ized by an abun dance of large tri lo bite bur rows, which are much rarer in Baltica. At least partly, this could be an ef fect of dif fer ences in fa cies, be cause Gondwanan clastic, usu ally heterolithic sed i - ments are more suit able for trace fos sil pres er va tion than are the more ho mo ge neous clastic or car bon ate lithologies pre vail - ing in Baltica (e.g., Rodríguez-Tovar et al., 2014) or an ef fect of in suf fi cient sur vey. In this pa per, a trace fos sil as sem blage in - clud ing large tri lo bite bur rows is de scribed from the Or do vi cian of the Holy Cross Moun tains in cen tral Po land. The Bukówka For ma tion stud ied be longs to the Kielce Re gion, a part of the Ma³opolska Block, which palaeogeographically is con sid ered as a peri-Bal tic ter rain (Cocks and Torsvik, 2002). This may shed light on pro vin cial dif fer ences be tween the Gond wana and
Baltica ichnological re cord. M oreover, this ichnological anal y sis pro vides in sight into the depositional palaeoenvironment of the Bukówka For ma tion, which has lacked de tailed ichnological stud ies. Only Trela (2006) no ticed a high de gree of bioturbation.
Body fos sils of the for ma tion were de scribed by au thors in clud - ing Bednarczyk (1971), Bednarczyk and Biernat (1978), Dzik and Pisera (1994), Bednarczyk and Stupnicka (2000).
GEOLOGICAL SETTING
The Or do vi cian of the Holy Cross Moun tains is de vel oped as a suc ces sion of siliciclastic and car bo na ceous de pos its of var ied thick ness that does not ex ceed 300 m (Skompski, 2015, for sum - mary), but rather less than 100 m in the Kielce Re gion (cf. Trela, 2006). The fa cies de vel op ment and thick ness were in flu enced by tec tonic re ju ve na tion of the sed i men tary ba sin at the be gin ning of the Or do vi cian. Gen er ally, Or do vi cian strata in the Kielce Re gion (the south ern block of the Holy Cross Moun tains) over lie the Cam brian strata with an an gu lar un con formity, un like the
£ysogóry Re gion (north ern block of the Holy Cross Moun tains), which is char ac ter ized by a con form able sed i men tary con tact be - tween Cam brian and Or do vi cian rocks (e.g., Czarnocki, 1939;
Bednarczyk, 1971). This re gion be longs to a larger struc ture called the Ma³opolska Block, which was sit u ated on the Baltica mar gin dur ing the Or do vi cian (e.g., Cocks, 2002) or be tween Baltica and Gond wana (Dzik and Pisera, 1994).
* Corresponding author, e-mail: michal.stachacz@uj.edu.pl Received: November 21, 2017; accepted: January 22, 2018; first published online: May 8, 2018
The Mid dle Or do vi cian Bukówka For ma tion crops out in only a few places of the Kielce Re gion, mainly in in ac tive quar ries of the Kielce area in the west and in the Miêdzygórz Quarry in the east. The Bukówka For ma tion is dated by the ar tic u late brachi o - pods Antigonambonites planus (Pan der), Lycophoria nucella (Dalman), Orthambonites calligramma (Dalman) and Productorthis obtusa (Pan der) to the late Arenig–ear li est Llanvirn (Bednarczyk, 1971; Dzik and Pisera, 1994; Trela, 2006; =late Dapingian–early Darriwilian, see Ogg et al., 2016), and is mainly rep re sented by fine-grained quartz arenites with scarce in ter ca - la tions of mudstones and siltstones. The quartz sand stones are gen er ally re placed by car bon ates to ward the top of the for ma tion (Trela, 2006). The Bukówka For ma tion lies above car bon ates of the Szumsko For ma tion and it is sep a rated from the over ly ing car bon ates of the Mójcza For ma tion by an un con formity (Trela, 2006). The Bukówka For ma tion ranges greatly in thick ness from 3 to 45 m and it is dated to the late Arenig and early Llanvirn (=late Dapingian and early Darriwilian, see Ogg et al., 2016; 470 Ma to 465 Ma) within three cono dont zones (Paroistodus originalis, Baltoniodus norrlandiscus and Eoplacognathus variabilis) and two graptolite zones (Didymo graptus hirundo Zone and Holmograptus lentus Subzone; Trela, 2006, based on Webby et al., 2004). Ac cord ing to Coo per and Sadler (2012; cf.
Ogg et al., 2016), these biozones rep re sent the late Dapingian–early Darriwilian, which cover ~4.5 My from 468.5 to 464 Ma (see also Ogg et al., 2016). Bergström et al. (2008) pro - posed the re gional sub di vi sions Volkhow and Kunda for Baltoscandia, which equal the late Dapingian and early Darriwilian. Nev er the less, the Baltoscandian sub di vi sions have been not yet been used for the Ma³opolska Block and pre cise cor re la tion is dif fi cult.
LOCALITIES
The Bukówka For ma tion was stud ied in two in ac tive quar - ries (Mójcza 1 and Mójcza 2) at Mójcza near Kielce, an in ac tive quarry at Miêdzygórz and a nat u ral ex po sure among an un - named stream trib u tary of the Czarna Staszowska River at Zalesie near £agów (Kielce County; Fig. 1). Poor ex po sures in the ra vine at Zalesie (GPS co or di nates: N50°50’29.2”, E20°41’11.4”) have pro vided sparse data and this lo cal ity is pro tected by Pol ish law as mon u ment of na ture. Two small, in - ac tive stone quar ries at Mójcza area were ex am ined in de tail, bed-by-bed and all beds have been sam pled and pol ished as part of the ob ser va tions. About 300 rock slabs were pre pared for de tailed ichnological and sedimentological anal y ses. The cat a logued sam ples are housed in the In sti tute of Geo log i cal Sci ences of the Jagiellonian Uni ver sity in Kraków (in sti tu tional ab bre vi a tion: INGUJ214P/B).
The Bukówka For ma tion sand stones were ex ploited as build ing stones dur ing the 20th cen tury, but re cently, most of the ex ploi ta tion sites have been cov ered by veg e ta tion. How - ever, slabs of the sand stone are ac ces si ble in walls of the Di o - cese Mu seum on the Czerwonego Krzy¿a and Jana Paw³a II streets, and in walls of the Pol ish Geo log i cal In sti tute, on Zgoda street, as well as on Zagórska street, all in Kielce. Some of the slabs con tain de ter mi na ble trace fos sils.
Mójcza re gion. The Bukówka For ma tion is ex posed in a few small, in ac tive quar ries, where two sec tions, 2 and 4 m thick, were stud ied (Fig. 1). In ad di tion, blocks of the un ex posed top of the for ma tion on Za³aŸna Hill at Mójcza were ex am ined (GPS co or di nates: N50°50’29.2”, E20°41’11.4”). Sim i lar rocks are ex posed in the stratotype of the Bukówka For ma tion at the Large cruzianid trace fossils in the Ordovician of the peri-Baltic area: the case of the Bukówka Formation... 401
Fig. 1. Location maps
A – sketch map of Poland; B – simplified geological map of the Paleozoic core of the Holy Cross Mountains; the geology is based on Trela (1998) and references cited therein
old quarry at Bukówka (Kielce dis trict, GPS co or di nates:
N50°50’16.1”, E20°39’43.3”; Fig. 1). The for ma tion in this area is com posed of quartz arenites with sparse siltstones and mudstone in ter ca la tions. The rocks were mostly stud ied in two aban doned quar ries Mójcza 1 and Mójcza 2, near Kielce. The Mójcza 1 sec tion (GPS co or di nates: N50°50’16.7” E:
20°41’16.0”; Figs. 1 and 2) rep re sents the lower part of the suc - ces sion stud ied. The bioturbated quartz sand stone beds dip nor mally at ~60°/19°. Sev eral beds of this sec tion con tain mass ac cu mu la tions of the brachi o pods Orthis sp. and
Orthanambonites sp., which are pre served al most ex clu sively as in ter nal and ex ter nal moulds (Figs. 2 and 3). How ever, cal - cite brachi o pod shells and one ho ri zon with moulds of the echinoderm Echinosphaerites are pres ent at the top of the for - ma tion (Fig. 3), which since re cently is no lon ger ex posed. The shells form shell pave ments in some beds. Sim i lar rocks con - tain ing the same trace fos sils and skel e tal fos sils of brachi o - pods and the gas tro pod ?Euomphalus (Fig. 3) prob a bly come from the old Bukówka Quarry. They were ob served in the wall slabs of sev eral build ings in Kielce.
Fig. 2. Logs of the late Dapingian–early Darriwilian Bukówka Formation, Mójcza 1 (lower) and 2 (upper) sections
Large cruzianid trace fossils in the Ordovician of the peri-Baltic area: the case of the Bukówka Formation... 403
Fig. 3. Primary sedimentary structures and body fossils in the sandstones of the Bukówka Formation of the Mójcza area A, B – hummocky cross-stratification; C, D – coquina beds with orthid brachiopod fossils: C – only moulds and negatives, D – well-preserved calcitic shells; E, F – Echinosphaerites sp.: E – individual specimen, F – horizon with abundant Echinosphaerites (E) and
orthid brachiopods (O); G – gastropod ?Euomphalus, wall in Zagórska Street, Kielce
In the Mójcza 2 sec tion (GPS co or di nates: N50°50’18.7”, E20°41’19.8”; Fig. 1), beds dip nor mally at ~140°/15° and rep - re sent the up per part of the suc ces sion stud ied. The sand - stones are mostly wackes, which are mostly to tally or al most to - tally bioturbated (ichnofabric in dex 4–5 sensu Droser and Bottjer, 1986). Pri mary sed i men tary struc tures are scarce, and are rep re sented by rare relicts of low-an gle cross strat i fi ca tion, rip ple and hor i zon tal lam i na tion (Fig. 2). A high con tent of ma trix as well as frag ments of re worked firmground intraclasts are com mon in sev eral beds.
The sandy lime stones in the up per part of the for ma tion ly - ing be low the dis con ti nu ity at Mójcza, which were for merly as - cribed to the Mójcza For ma tion by Dzik and Pisera (1994), were in cluded in the Bukówka For ma tion by Trela (2006). The trace fos sils from sand stones of the Mójcza sec tions be long to hor i - zon tal pascichnia and ver ti cal domichnia. The pascichnia in - clude Planolites montanus, P. beverleyensis, Palaeophycus isp. and Cruziana isp. The domichnia are rep re sented by Skolithos isp. and ?Catenarichnus isp. The cubichnia in clude Rusophycus isp. and Rusophycus ?pudicus and fodinichnia Teichichnus isp.
Miêdzygórz Quarry. The quarry (GPS co or di nates:
N50°44’8.4”, E21°33’47.1”; Fig. 1) ex poses thick-bed ded glauconitic sand stones and con glom er ates of the Miêdzygórz For ma tion, sand stones of the Bukówka For ma tion, and very poorly ex posed lime stones of the Mójcza For ma tion (Dzik and Pisera, 1994; Bednarczyk and Stupnicka, 2000; Trela, 2006).
Con glom er ates of the Miêdzygórz For ma tion con sist of 2–60 mm clasts and glauconitic ma trix, which are interbedded with green, coarse-grained sand stones (Tomczyk, 1962;
Tomczyk and Turnau-Morawska, 1967). They do not con tain any trace fos sils. The over ly ing Bukówka For ma tion is com - posed of yel low ish and grey sand stones. The Bukówka For ma - tion is poorly ex posed in Miêdzygórz Quarry and does not show im por tant dif fer ences in ichnological and sedimentological fea - tures be tween this quarry and rocks ex posed in the Mójcza re - gion, which were ana lysed in de tail. Ac cord ing to Bednarczyk and Stupnicka (2000), the lithostratigraphic units in this quarry are cut by sev eral faults. There fore, it is im pos si ble to mea sure the en tire sec tion.
TRACE FOSSILS
Cruziana isp.
(Fig. 4)
M a t e r i a l. – Two cat a logued spec i mens, INGUJ214P/B3, B26; plus one spec i men in a slab in the wall of the Pol ish Geo log i cal In sti tute on Zgoda street in Kielce.
D e s c r i p t i o n. – A frag ment of a large, high, in dis tinctly bilobate hypichnial ridge, 80–120 mm wide, 20–50 mm high, was ob served for a length of 340 mm. The lobes are sep a rated by an in dis tinct, shal low fur row and cov ered by in dis tinct, vari - able, thicker and thin ner scratch traces or imbricated scales (e.g., spec i men INGUJ214P/B26). At the top of the lobes, blunt scratch traces 1–3 mm wide are pres ent. They run al most per - pen dic u lar to the me dian fur row. The spec i men INGUJ214P/B3 shows scratch traces in the ex ter nal sides of the lobes. They are ~0.5 mm wide, sharp, ar cu ate and oblique to the me dian fur row. The ob served bur rows are cross-cut by nu mer ous Skolithos. Cross-sec tions of the bur row dis play a mas sive fill, which is lithologically the same as the host rock (Fig. 4C). The
spec i men in the wall of the build ing is pre served as an epichnial, bilobate fur row, which is ~50 mm wide and shows a sim i lar pat - tern of scratch traces.
R e m a r k s. – The Cruziana col lected and de scribed is sep a rated by a thin siltstone layer from the un der ly ing sand - stone bed. The thick scratch traces are poorly pre served. The spec i mens de scribed, es pe cially spec i men INGUJ214P/B26, are quite sim i lar to Cruziana imbricata Seilacher, 1970, but they show both an imbricated pat tern and scratch traces, in con trast to C. imbricata, which dis plays no scratch traces (Seilacher, 1970). Nev er the less, their poor pres er va tion pre vents de ter mi - na tion at the ichnospecies level. The sand stone bed bear ing Cruziana is no tice ably thicker around the trace. This sug gests that the trace-mak ing tri lo bite bur rowed in a small, lo cal de pres - sion on the seafloor. The ab sence of dis tur bance in the sand - stone bed above the trace points to the predepositional or i gin of the trace by the fill ing of a fur row with sand brought in by cur - rents (Baldwin 1977b), un like the large, teichichnoid Cruziana from the Or do vi cian of Por tu gal, Eng land and Spain (Goldring, 1985; Neto de Carvalho, 2006; Stachacz et al., 2015).
Rusophycus isp.
(Fig. 5A–D)
M a t e r i a l. – Eight spec i mens, INGUJ214P/B1, B4, B5, B17, B2729.
D e s c r i p t i o n. – Frag ments of bilobate hypichnial mounds with out dis tinct mar gins (Fig. 5A–C) or with an in dis - tinct slat at one side (Fig. 5D), 60–200 mm long, 60–110 mm wide, and 10–30 mm high. The me dian fur row is ex panded on the fron tal side, so the lobes show a cleft, V-shaped pat tern.
The lobes are cov ered by thick, ir reg u lar scratch traces, which are ~1–5 mm wide. The scratch traces meet at an an gle of 100–180°, be ing nearly per pen dic u lar (Fig. 5A) or oblique to the me dian fur row. In the lat ter case, they form V-shaped pat terns ori ented in op po site di rec tions in the fron tal and rear parts (Fig. 5B, C).
R e m a r k s. – Some spec i mens are so poorly pre served (Fig. 5A, B) that they re sem ble in or ganic load casts. How ever, their true na ture is re vealed by the scratch traces or even moulds of limbs, seen in the in dis tinct mar ginal ar eas (Fig. 5B).
The sand stone bed around Rusophycus isp. is rel a tively thick.
This sug gests that the trace-mak ing tri lo bite bur rowed in a small, lo cal de pres sion on the sea floor and next the bed was loaded dur ing de po si tion on top of the trace, if the bur row was predepositional.
Rusophycus ?pudicus Hall, 1852 (Fig. 5E)
M a t e r i a l. – Two spec i mens, INGUJ214P/B2, B30.
D e s c r i p t i o n. – Elon gate, bilobate hypichnial mound, wedge-shaped in out line, at least 130 mm long, 60–70 mm wide, 30 mm high, with out dis tinct mar gins. The lobes are cov - ered by more or less dis tinct, weakly de vel oped scratch traces, which are ~1 mm wide and 1–2 mm apart. They meet in the me - dian fur row at dif fer ent an gles: at 90° in the front part, with a tran si tion to 120° in the rear part. The scratch traces are curved in an arc and form a V-shaped pat tern. They are ori ented in op - po site di rec tions in the front and rear parts of the trace fos sil.
Large cruzianid trace fossils in the Ordovician of the peri-Baltic area: the case of the Bukówka Formation... 405
The scratch traces in the front part are slightly thicker than those in the rear part.
R e m a r k s. – The spec i mens de scribed here are sim i lar to Rusophycus pudicus Hall, 1852 from the Do min ion For ma - tion (Arenig, Wabana Group, New found land, E Can ada), il lus - trated by Fillion and Pickerill (1990: pl. 15.6) and per son ally ob - served, but its state of pres er va tion does not per mit such an ex - act de ter mi na tion. The tri lo bite Flexicalymene is con sid ered as the pro ducer of Rusophycus pudicus as its size and shape re - sem bles the mor phol ogy of this trace fos sil and im prints of its ce phalic doublure and tho racic pleurae were ob served in some spec i mens (Osgood, 1970). More over, Osgood (1970) found Flexicalymene meeki Foerste to gether with Rusophycus pudicus. Flexicalymene and other calymenids orig i nated in Gond wana and were dis trib uted around Gond wana, Laurentia and Baltica at the end of the Or do vi cian (Barnes et al., 1996).
Skolithos isp.
(Fig. 6A, B)
M a t e r i a l. – Seven sand stone slabs, INGUJ214P/B6, B9, B11, B13, B14, B16, B25, which con tain more than thirty spec i mens. A few hun dred spec i mens were ob served in the field.
D e s c r i p t i o n. – Ver ti cal or sub-ver ti cal pipe-like, lined shafts filled with sand, vis i ble in ver ti cal sec tions or on bed ding sur faces. Most of the shafts are gen er ally con stant in width, at ~5 mm, and the larg est are up to 18 mm in di am e ter.
Their ob served length, up to 100 mm, de pends on the bed thick ness; it is lon ger in thicker beds. The pipes are densely packed in some beds.
Fig. 4. Cruziana isp. from the Ordovician Bukówka Formation, Mójcza
A, B – general view of hypichnial convex semi-reliefs display scratch traces; associated trace fossils (S – Skolithos, P – Planolites) occur: A – INGUJ214P/B3, B – INGUJ214P/B26; C – vertical section of the hypichnial convex semirelief with massive fill, INGUJ214P/B3
Fig. 5. Rusophycus from the Bukówka Formation at Mójcza
A, B – poorly pre served Rusophycus isp. with only partly vis i ble scratch traces: A – hypichnial view, B – side view of the same spec i men with limbs traces at the side ar rowed, INGUJ214P/B4; C, D – bilobate spec i mens of Rusophycus isp. with dis tinct scratch traces, hypichnial con vex semireliefs: C – INGUJ214P/B27, D – INGUJ214P/B1; E – Rusophycus ?pudicus Hall, 1852, hypichnial con vex semirelief, INGUJ214P/B2
Large cruzianid trace fossils in the Ordovician of the peri-Baltic area: the case of the Bukówka Formation... 407
Fig. 6. Other trace fossils from the Bukówka Formation at Mójcza
A, B – Skolithos isp.: A – bioturbated up per bed ding sur face, INGUJ214P/B6, B – endichnion in sand stone bed, field photo; C, D – Teichichnus rectus Seilacher, 1955 (T): C – endichnion sep a rated from the host bed, side view, INGUJ214P/B24, D – endichnion in a thin sand stone bed, lower bed ding sur face, P – Planolites, INGUJ214P/B31; E – Planolites beverleyensis (Bill ings, 1862), hypichnial con vex semirelief, a slab in the wall by the Œwiêtego Krzy¿a Street, Kielce; F – Planolites montanus Rich ter, 1937, hypichnial con vex semi-re lief, INGUJ214P/B7; G – Palaeophycus tubularis (Hall, 1847), endichnia in block of me dium sand stone beds in the wall, Jana Paw³a II street, Kielce; H – ?Catenarichnus isp., endichnion in a sand stone bed, NGUJ214P/B8; I – Phycodes cf. circinatus Rich ter, 1850; J –
?Ptychoplasma isp; both spec i mens are hypichnia in the wall of the build ing of the Pol ish Geo log i cal In sti tute, Zgoda street, Kielce
R e m a r k s. – Ac cord ing to Hal lam and Swett (1966), trun cated Monocraterion can be sim i lar to Skolithos, how ever, the lat ter is usu ally lined, and no ev i dence of a fun nel, a typ i cal fea ture of Monocraterion (Schlirf and Uchman, 2005), was ob - served in the Skolithos isp. de scribed. Skolithos is com monly in ter preted as a domichnial bur row of sus pen sion-feed ing annelids or phoronids (Alpert, 1974; Fillion and Pickerill, 1990;
Vinn and Wil son, 2013).
Teichichnus rectus Seilacher, 1955 (Fig. 6C, D)
M a t e r i a l. – Two sand stone slabs INGUJ214P/B24, B31, five spec i mens ob served in the field.
D e s c r i p t i o n. – Endichnial, wedge- or ba nana-shaped struc tures pre served in full re lief with more or less dis tinct U-shaped, retrusive spreites. The struc ture is 8–10 mm wide, 10–20 mm high, at least up to 65 mm long.
R e m a r k s. – The spec i mens ana lysed vary in shape and size. Teichichnus rectus is the type ichnospecies of this ichnogenus, com monly in ter preted as an equi lib rium feed ing struc ture (Cor ner and Fjalstad, 1993).
Planolites beverleyensis (Bill ings, 1862) (Fig. 6E)
M a t e r i a l. – Three spec i mens, INGUJ214P/B18–20, nu mer ous spec i mens ob served in the field.
D e s c r i p t i o n. – Hor i zon tal, straight or slightly curved hypichnial ridge pre served in semirelief, semi-el lip ti cal or semi-cir cu lar in cross-sec tion, with smooth sur face, at least 85 mm long. Its width ranges from 4 to 9 mm but it is uni form through the whole length. The ridges are filled by sandy ma te - rial iden ti cal to that of the host sand stone bed.
R e m a r k s. – Some spec i mens pre served in sand stone (e.g., INGUJ214P/B20) are sim i lar to Palaeophycus tubularis Hall, 1847. Nev er the less, the lat ter taxon dif fers by the pres - ence of a wall (Pem ber ton and Frey, 1982; Fillion and Pickerill, 1990; Keighley and Pickerill, 1995). Planolites is pres ent in many fa cies and it is in ter preted as an ac tively filled pascichnion formed by worm-like de posit-feed ers (e.g., Osgood, 1970;
Pem ber ton and Frey, 1982; Fillion and Pickerill, 1990; Keighley and Pickerill, 1995).
Planolites montanus Rich ter, 1937 (Fig. 6F)
M a t e r i a l. – Two sand stone slabs (INGUJ214P/B7, B21) that con tain sev eral spec i mens; nu mer ous spec i mens ob - served in the field.
D e s c r i p t i o n. – An endichnial full-re lief cyl in der or a hypichnial ridge, 3–5 mm wide, with smooth sur faces, pre - served in full re lief or semirelief. The bur row is curved, semi-oval in cross-sec tion, chang ing course over short dis - tances. Com monly, it pro trudes from or plunges into the bed.
Some spec i mens ob served are pre served in a silty layer within a hummocky cross-strat i fied sand stone bed. The trace fos sil is abun dant in some sand stone beds and densely cov ers their soles (Fig. 6F).
R e m a r k s. – Ac cord ing to Pem ber ton and Frey (1982), Planolites montanus is rel a tively small, curved or con torted, up to 5 mm in di am e ter. How ever, the size of spec i mens is a less im por tant di ag nos tic fea ture; more im por tant is the char ac ter is - tic ori en ta tion chang ing over short dis tances and rel a tively com - monly plung ing into the bed.
Palaeophycus tubularis Hall, 1847 (Fig. 6G)
M a t e r i a l. – Five spec i mens ob served in slabs in the wall of the Di o cese Mu seum (Czerwonego Krzy¿a and Jana Paw³a II streets, Kielce); a few spec i mens ob served in the field.
D e s c r i p t i o n. – Endichnial, straight or slightly curved, un branched tubes, 4–15 mm wide, from tens to 200 mm long, cir cu lar or oval in cross-sec tion, with a more or less dis tinct wall.
The fill ing is the same as the host sand stone.
R e m a r k s. – Some spec i mens are dif fi cult to dis tin guish from Planolites beverleyensis (Bill ings, 1862). How ever, the pres ence of the wall in di cates Palaeophycus tubularis (see Pem ber ton and Frey, 1982; Fillion and Pickerill, 1990; Keighley and Pickerill, 1995). Palaeophycus tubularis is mostly in ter - preted as a struc ture formed by de posit feed ers and pred a tors mov ing mainly along the sed i ment in ter faces (e.g., Pem ber ton and Frey, 1982).
?Catenarichnus isp.
(Fig. 6H)
M a t e r i a l. – One sand stone frag ment (spec i men INGUJ214P/B8) with two poorly pre served spec i mens. In ad di - tion, spec i mens in slabs in the wall of the build ing of the Pol ish Geo log i cal In sti tute, Zgoda street, Kielce.
D e s c r i p t i o n. – A J- or U-shaped bur row whose limbs di verge. The cyl in der is ~12 mm wide and 20–20 mm deep. The bur row is un lined. It has a rough sur face and sandy fill ing, match ing the host rock.
R e m a r k s. – Catenarichnus Bradshaw, 2002 and its only ichnospecies C. antarcticus Bradshaw, 2002 from the De - vo nian of Antarctica is a ver ti cal arc-like cy lin dri cal bur row, with di ver gent limbs which plunge into the bed at a low an gle.
Catenichnus contentus Mc Car thy, 1979 is sim i lar but it shows in dis tinct spreite and then dif fers from Arenicolites Salter, 1857.
Arenicolites has par al lel limbs and the afore men tioned ichnogenera are char ac ter ized by di ver gent limbs (see Hofmann et al., 2011, Rodríguez-Tovar et al., 2014). A Cam - brian trace fos sil of this type with strongly di ver gent arms, de ter - mined as Arenicolites (Stachacz, 2016) may be long to Catenarichnus.
Phycodes cf. circinatus Rich ter, 1850 (Fig. 6I)
M a t e r i a l. – One spec i men ob served in the wall of the build ing of the Pol ish Geo log i cal In sti tute, Zgoda street, Kielce, and a few poorly pre served spec i mens ob served in the field.
D e s c r i p t i o n. – Hypichnial, gen er ally hor i zon tal, curved, loosely spaced branched ridges ar ranged in an in dis - tinct fan, pre served in semi-re lief in a bioturbated sand stone
bed. At least six branches di verge prob a bly from a com mon stem, but the meet ing point of the branches and the com mon stem are not pre served. Parts of the ridges are al most par al lel to each other, while oth ers are di ver gent. The ridges are cir cu lar to oval in cross-sec tion, 8–12 mm wide, ~13 mm long. Their sur face is rough, even or in dis tinctly undulose.
R e m a r k s. – The spec i men de scribed is poorly pre - served; how ever, its mor pho log i cal fea tures are shared with Phycodes circinatus Rich ter, 1850 (cf. Häntzschel, 1975; Fillion and Pickerill, 1990; Seilacher, 2000; Stachacz, 2016).
Phycodes is a fodinichnion pro duced by un known or gan isms; in the Pa leo zoic it is known mostly from shal low-ma rine strata (e.g., Osgood, 1970; Fillion and Pickerill, 1990; Seilacher, 2000;
Hanken et al., 2016).
?Ptychoplasma isp.
(Fig. 6J)
M a t e r i a l. – Sev eral spec i mens ob served in the wall of the build ing of the Pol ish Geo log i cal In sti tute, Zgoda street, Kielce.
D e s c r i p t i o n. – Hypichnial ridges 12–20 mm wide, com posed of oval, ar row-shaped or ir reg u lar, smooth pads;
some of which are sep a rated by more even seg ments. The pads are 10–40 mm long, ~10 mm high and only slightly wider than the even ridge. The over all course is straight or gently wind ing; some seg ments in ter sect.
R e m a r k s. – The fill shows some sim i lar i ties to Torrowangea rosei Webby, 1970, but the lat ter taxon is dis - tinctly sin u ous to me an der ing and much smaller (cf. Webby, 1970; Gámez Vintaned et al., 2006). Ptychoplasma is a lo co - mo tion trace of molluscs; it is known since the Cam brian (Uchman et al., 2011).
DISCUSSION
DEPOSITIONAL ENVIRONMENT
The rec og niz able trace fos sils from the Bukówka For ma tion are rel a tively of low di ver sity, and show in fre quent and usu ally bad pres er va tion. The ichnoassemblage con sists of eleven ichnotaxa, in clud ing fodinichnia (Teichichnus, Phycodes, Ptychoplasma), pascichnia (Cruziana, Planolites, Palaeophycus), domichnia (Skolithos, Catenarichnus) and cubichnia (Rusophycus). The pres ence of both hor i zon tal and ver ti cal bur rows is typ i cal of the ar che typal and prox i mal Cruziana ichnofacies sug gest ing de po si tion in the up per to lower shoreface with storm in flu ences (cf. Pem ber ton et al., 2001). Some parts of the for ma tion may be long to the Skolithos ichnofacies (sensu Seilacher, 1967) but any se ries of beds con - tain ing ex clu sively ver ti cal traces has not been ob served in the field. The in ter pre ta tion of ichnofacies is in ac cor dance with the pres ence of hummocky cross-strat i fi ca tion, low-an gle cross-lam i na tion, rip ple lami na tions and hor i zon tal lam i na tion (Fig. 2), a set of pri mary sed i men tary struc tures typ i cal of a wave- and storm-dom i nated shoreface. The lower part of the Bukówka For ma tion, which is rep re sented by thick-bed ded sand stones bear ing ir reg u larly scat tered brachi o pod co quina beds, len tic u lar brachi o pod ac cu mu la tions, and shell pave - ments might be re ferred to a pe ri odic in ten si fi ca tion of storm events (cf. D¿u³yñski and Kubicz, 1975; Kidwell, 1986). The skel e tal fos sils are well-pre served, sug gest ing their rapid burial.
(cf. Brett and Baird, 1988). In this part of the for ma tion, the de - gree of bioturbation is high. How ever, the bioturbation struc - tures are sub tle and small. The lack of in-situ ro ta tions of shells in shell pave ments sug gests bioturbation only by small or gan - isms. The shell ac cu mu la tions and the pres er va tion of pri mary sed i men tary struc tures in di cate higher-en ergy ep i sodes with rapid sed i men ta tion when the col o ni za tion win dow was too brief. How ever, the pre vail ing bioturbated sed i ments sug gest a mostly low ac cu mu la tion rate and lon ger col o ni za tion win dow af ter the storm events, en abling oblit er a tion of pri mary struc - tures by bur row ing or gan isms. The sedimentological data in di - cate that the sed i men ta tion rate of the Bukówka For ma tion var - ied. Strongly bioturbated sand stones of the up per part of the for ma tion re quired a very low sed i men ta tion rate, when bioturbation re work ing bal anced the sed i ment ac cu mu la tion. A low sed i men ta tion rate in the ba sin is also sug gested by firmgrounds, the pres ence of which is in di rectly ev i denced by intraclasts.
The pos tu lated over all low sed i men ta tion rate in ter rupted by short-term storm events is partly in op po si tion to the view of Bednarczyk and Biernat (1978), who con cluded that the for ma - tion, 30 m thick, was rap idly de pos ited in the east ern and the west ern nearshore mar gins of the ba sin, as op posed to the cen tral area, in clud ing the Kielce (also the sec tions at Mójcza in this study) and the Bardo Syncline ar eas, where the sed i men ta - tion rate was much lower; all be cause of tec tonic ac tiv ity dur ing the Floian and Dapingian.
The ab sence of well-pre served trace fos sils, es pe cially cruzianids, was prob a bly caused by in tense bioturbation of the sandy de pos its (ichnofabric in dex 4–6 sensu Droser and Bottjer, 1986) and the ab sence of muddy in ter ca la tions which would have a large pos i tive in flu ence on the pres er va tion po - ten tial of such struc tures, es pe cially their scratch traces. The high est pres er va tion po ten tial for such traces is in heterolithic siltstone-sand stone de pos its. Also the pres ence of brachi o pod shell grounds lim ited bur row ing ac tiv ity and de creased the preservational po ten tial of traces.
Tak ing into ac count the du ra tion of de po si tion of the Bukówka For ma tion that lasted 4.5–5 My (from the late Dapingian to the early Darriwilian) and its max i mum thick ness, an av er age sed i men ta tion rate of 9 cm/1000 y is es ti mated.
This is a low value for shal low-ma rine sandy sed i ments, sup - ported by the gen er ally high bioturbation de gree of the sand - stones in ves ti gated. Up-sec tion, the sed i men ta tion rate in the Kielce Re gion was gen er ally even lower as can be in ferred from the over ly ing con densed lime stones of the Mójcza For ma tion (Dzik and Pisera, 1994; Trela, 2005b). The tran si tion from bioturbated quartz sand stones with storm ac cu mu la tions of brachi o pod shells through sand stones (es pe cially wackes) with firmground intraclasts and rarely mudstones with in ter ca la tions to cal car e ous sand stones and sandy lime stones in di cates a de - creas ing fre quency of storm events, pro gres sive re duc tion in wave/cur rent strength and grad ual ces sa tion of clastic de po si - tion. Such changes in sed i men ta tion char ac ter are usu ally at - trib uted to sea level rise. This in ter pre ta tion is also sup ported by grad ual re place ment of clastic de po si tion by car bon ates to ward the top of the for ma tion and the pres ence of highly con densed lime stones over ly ing the Bukówka For ma tion (Trela, 1998, 2006). Ac cord ing to Trela (2017), the Bukówka For ma tion was de pos ited dur ing re gres sion fol low ing the early Dapingian (Baltoniodus navis Zone) trans gres sion, which was re corded also in the £ysogóry Re gion (Trela, 2008). The con densed Mójcza Lime stone over ly ing the Bukówka For ma tion was de - pos ited dur ing the next transgressive phase which started in the late Darriwilian Pygodus serra Zone (Trela, 2005a, b, 2006).
The dis con ti nu ity mark ing the bound ary be tween the Bukówka Large cruzianid trace fossils in the Ordovician of the peri-Baltic area: the case of the Bukówka Formation... 409
For ma tion and the Mójcza For ma tion (Trela, 2006) is as so ci - ated with sub ma rine ero sion that took place dur ing a sea level fall and was in ter preted as the Viruan dis con ti nu ity sur face known from Swe den (Dzik and Pisera, 1994). The Viruan dis - con ti nu ity is con nected with a global eustatic sea level fall that took place in Baltoscandia (Holmer, 1983). A world wide long-term sea level fall took place from the Dapingian to early Darriwilian, which was in ter rupted by higher fre quency short-term sea level rises and falls (Dronov and Holmer, 1999;
Haq and Schutter, 2008; Dronov et al., 2011; Dronov, 2017).
Ac cord ing to Trela (2004), the Or do vi cian of the Ma³opolska Block re cords three highstands and lowstands as so ci ated with sec ond or der sea level changes. How ever, tec tonic ac tiv ity in the Holy Cross Moun tains dur ing the Or do vi cian in flu enced the sed i men tary re cord of these cy cles, and, as a re sult, the se - quence bound aries here have a lo cal mean ing (Trela, 2008).
More over, the fa cies and sed i men ta tion rate dis tinctly var ied (Bednarczyk and Biernat, 1978). Nev er the less, the fos sil re cord in the Holy Cross Moun tains dis plays a gen er ally long-term transgressive trend dur ing the Or do vi cian (cf. Haq and Schutter, 2008: fig. 1), whilst strongly bioturbated, storm-dom i - nated sand stones of the Bukówka For ma tion were de pos ited dur ing a brief in ter val of rel a tively low sea level, or short-term re - gres sion, as pos tu lated Trela (2017). The tran si tion from siliciclastic to car bon ate fa cies at the top of the Bukówka For - ma tion is in ter preted in this study as a short-term trans gres sion re cord, which rep re sents the sec ond of the two lower-or der transgressive pulses that oc curred dur ing the late Dapingian and early Darriwilian from ~470 Ma to 464 Ma (cf. Trela, 2005a, fig. 7; Haq and Schutter, 2008: fig. 1).
THE BUKÓWKA FORMATION IN THE CONTEXT OF THE ICHNOLOGY OF BALTICA AND GONDWANA AREAS
The lo ca tion of the Bukówka For ma tion be tween the main land masses of Baltica and Gond wana makes it im por tant in the dis cus sion of ichnological dif fer ences be tween the de pos its of these con ti nents, even though the data are ham pered by poor ex po sure of the de pos its and poor pres er va tion of their trace fos sils. The lime stones of the over ly ing Mójcza For ma tion are highly con densed and ho mog e nized by bioturbation, in con trast to Or do vi cian lime stones of the Baltica mar gin, which are also bioturbated, com monly con densed but lo cally con tain well-pre - served trace fos sils (e.g., Dronov et al., 2002; Cherns et al., 2006; Dronov and Mikuláš, 2010; Knaust et al., 2012; Dronov,
2013; Knaust and Dronov, 2013; Vinn et al., 2014b, 2015; Vinn and Toom, 2016; Toom et al., 2017).
Quartz sand stone-dom i nated fa cies of the same age as the Bukówka For ma tion are known in peri-Gondwanan ar eas, mostly in the Armori can Quartz ite For ma tion, the fa cies and ichnology of which are well-known from the Ibe rian Pen in sula and France (ref er ences be low). They are rel a tively poorly bioturbated, but they con tain di verse and usu ally well-pre - served ichnoassemblages, which in clude at least 35 ichnospecies of 20 ichnogenera de scribed by sev eral au thors (Rouault, 1850; Romano, 1974, 1991; Crimes and Marcos, 1976, Baldwin, 1977a, b; Pickerill et al., 1984; Durand, 1984, 1985a, b; Aceñolaza et al., 2008; Rodríguez-Tovar et al., 2014).
An other peri-Gondwanan (Avalonian) unit, i.e. the Bell Is land Group of New found land, sim i lar to the Armori can Quartz ite and partly of the same age, in cludes ~97 ichnotaxa (Fillion and Pickerill, 1990). The Bell Is land Group is also dis tinctly less bioturbated than the Bukówka For ma tion. The thick ness of these units is much larger than that of the Bukówka For ma tion, i.e. ~1390 m for the Bell Is land Group (Fillion and Pickerill, 1990) and up to 600 m (usu ally 150–300 m but in some cases
<10 m) for the Armori can Quartz ite (Gutiérrez-Marco et al., 2002). This sug gests their much higher sed i men ta tion rate and, as a con se quence, deeper burial of or ganic mat ter and its higher con tent deeper in the sed i ment (cf. Ingall and Cappellen, 1990). Low sed i men ta tion rate causes a low burial rate of or - ganic mat ter (Müller and Suess, 1979; Jung et al., 1997;
Löwemark et al., 2006) which is con cen trated shal lowly in the sed i ment, con sumed and burnt down in oxic en vi ron ments (Wetzel and Uchman, 2017). Ac cord ingly, a higher sed i men ta - tion rate causes deeper burial of or ganic mat ter, which at tracted bur row ing or gan isms. In the case of the peri-Gondwanan ar - eas, the rel a tively high sed i men ta tion rate pro moted both deeper bur row ing and better pres er va tion of trace fos sils. A slow sed i men ta tion rate in Baltica caused quick de com po si tion of or ganic mat ter and its shal low burial. Shal low bur row ing neg - a tively in flu enced the di ver sity of traces and their pres er va tion.
The pres er va tion po ten tial of trace fos sils in sandy de pos its of the Bukówka For ma tion was much lower than in many Avalonian and peri-Gondwanan sec tions (e.g., ïOrbigny, 1842;
Rouault, 1850; Lebesconte, 1883, 1886; Delgado, 1886;
Seilacher, 1970; Baldwin 1977a; Durand, 1984, 1985a, b;
Fillion and Pickerill, 1990; Neto de Carvalho, 2006), and com - pa ra ble to the siliciclastic-cool wa ter car bo na ceous sed i ments of Baltica that con tain sim i lar bur rows plus bor ings (~20
Fig. 7. Model of differences in the ichnological record between peri-Gondwana, the Ma³opolska Block and Baltica during the Ordovician, the differences depend on accumulation rate, burial of organic matter and depth of burrowing
ichnotaxa, based on: Cherns et al., 2006; Dronov and Mikuláš, 2010; Vinn and Wil son, 2010; Knaust et al., 2012; Knaust and Dronov, 2013; Vinn et al., 2014a; Vinn and Toom, 2016; Toom et al., 2017). This fact ex plains the pro vin cial dif fer ences in the Or do vi cian ichnoassemblages of Gond wana and Baltica, which were at least partly driven by the re gional pres er va tion con di - tions. Nev er the less, the low ichnodiversity and poor pres er va - tion of the trace fos sils from the Bukówka For ma tion re sults also from spe cific depositional con di tions in a shal low-wa ter en vi ron - ment in flu enced by storms, in which most of the sed i ment was re peat edly re-de pos ited be cause of a lack of ac com mo da tion space and rel a tively strong waves/cur rents.
The most com mon trace fos sils of the Bukówka For ma tion have no great strati graphic and palaeo geo graphi cal sig nif i - cance. Nev er the less, the large Cruziana and Rusophycus cor - re spond to the Cruziana imbricata and C. pudica groups (sensu Seilacher, 1970), which are char ac ter ized by large sizes of traces and are typ i cal of the peri-Gondwanan realm (e.g., Delgado, 1886; Seilacher, 1970; Durand, 1985a, b; Mángano and Buatois, 2003; Neto de Carvalho, 2006; Neto de Carvalho and Baucon, 2016). The large size of cruzianids is at trib uted to cool-wa ter con di tions at high lat i tudes and ‘po lar gi gan tism’
(Dronov, 2013; Neto de Carvalho and Baucon, 2016) and this con cerns also Or do vi cian of the Ma³opolska Block. They are rarely noted in Baltica. Nev er the less, tri lo bite bur rows pre - served with their body fos sils in the Mid dle Or do vi cian lime - stones of Swe den were il lus trated by Cherns et al. (2006).
More over, Kushlina and Dronov (2011) de scribed a gi ant Or do - vi cian Rusophycus from Si be ria. Vinn and Toom (2016) ana - lysed other ar thro pod traces from the car bon ate fa cies in the Or do vi cian and Si lu rian of Es to nia. Knaust (2004) re ported a few tri lo bite trace fos sils from the Baltica mar gins of Nor way, re - sem bling those from the Gondwanan realm. More over, the pres ence of Rusophycus ?pudicus in the peri-Bal tic Bukówka For ma tion sug gests its sim i lar i ties to the peri-Gondwanan (in - clud ing Avalonia) realm. The pre vail ing cool-wa ter car bon ate and con densed fa cies in Baltica are char ac ter ized by a scar city of cruzianids. Also, other trace fos sils re ported from the car bon - ate rocks of Baltoscandia are usu ally poorly pre served and mod er ately di verse (Vinn and Toom, 2016, Toom et al., 2017).
This could be an ef fect of gen er ally shal low bur row ing and much lower pres er va tion po ten tial in the car bon ate (even in de - tri tal car bon ate) than siliciclastic set tings, es pe cially in the case of very low sed i men ta tion rates in cool wa ter car bon ate en vi ron - ments (Fig. 7). How ever, in some set tings, trace fos sils in car - bon ate fa cies can be well-pre served, e.g. by con ser va tion of the
sed i ment sur face, in clud ing traces, by mi cro bial mats and biofilms (Knaust et al., 2012). The clastic de pos its of the Bukówka For ma tion with rare and rel a tively large cruzianids may rep re sent a sim i lar de po si tion rate to that of the cool-wa ter lime stones of Baltica (cf. Dronov, 2013).
Deep sed i ment bur row ing is a less ef fec tive way of feed ing in con densed fa cies, where food is con cen trated on or very near the sed i ment-wa ter in ter face. More over, early ce men ta - tion at shal low depths in the sed i ment and the com mon for ma - tion of firm- and hardgrounds do not fa vour bur row ing. In such sit u a tions, bur rows or bor ings of ses sile ben thic or gan isms are more fre quent, as in the case of Baltica. Sum ma riz ing, it seems that the ichnological dif fer ences among Gond wana, Baltica, and ter ranes did not re sult purely from the palaeogeographic ranges of trace mak ers, but in stead were strongly in flu enced by taphonomic pro cesses re lated to sed i men ta tion rate and burial of or ganic mat ter.
CONCLUSIONS
The Mid dle Or do vi cian Bukówka For ma tion shows poorly pre - served trace fos sils of low di ver sity, in clud ing large Cruziana and Rusophycus prob a bly be long ing to the Cruziana imbricata group.
They in di cate that this for ma tion was de pos ited in a wave-dom i - nated shoreface with storm ep i sodes dur ing a gen eral trans gres - sion. The trace-mak ing or gan isms ev i dently bur rowed shal lowly be cause or ganic mat ter was con cen trated near the sed i ment-wa - ter in ter face in a gen er ally low sed i men ta tion rate re gime. Dif fer - ences in sed i men ta tion rate, the burial of or ganic mat ter and sed i - ment type were the fac tors which strongly in flu enced ichnological dif fer ences be tween the Or do vi cian of Baltica, Gond wana, and ter rains lo cated be tween them, in clud ing the Ma³opolska Block on which the Bukówka For ma tion oc curs.
Ac knowl edge ments. Jagiellonian Uni ver sity sup ported the stud ies by M.S. (DSC funds, no. DS/MND/Wbi - NoZ/ ING/1/2012), W. £. (DSC funds, no. DS/MND/Wbi - NoZ/ING/2016) on the Or do vi cian rocks in the Holy Cross Moun tains, and by A.U. (DS, K/ZDS/005424). A. Dronov (Mos - cow, Rus sia), A. Sá (Vila Real, Por tu gal), W. Trela (Kielce, Po - land) and O. Vinn (Tartu, Es to nia) pro vided con struc tive re - views, how ever, some re viewer’s opin ions have not been fol - lowed. An drew K. Rindsberg im proved the Eng lish in most of the pa per.
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