Tu bu lar tempestites from Ju ras sic mudstones of south ern Po land
Paulina LEONOWICZ1, *
1 Uni ver sity of War saw, Fac ulty of Ge ol ogy, Żwirki i Wigury 93, 02-089 Warszawa, Po land
Leonowicz, P., 2016. Tu bu lar tempestites from Ju ras sic mudstones of south ern Po land. Geo log i cal Quar terly, 60 (2):
385–394, doi: 10.7306/gq.1246
This pa per pres ents tu bu lar tempestites from south ern Po land and their ap pli ca tion for en vi ron men tal and se quence stra tig - ra phy in ter pre ta tion. Tu bu lar tempestites are pres ent in muddy suc ces sions of the Lower Ju ras sic Ciechocinek For ma tion and in the Mid dle Ju ras sic Częstochowa Ore-Bear ing Clay For ma tion in the Silesian-Kraków re gion. They oc cur as sand-filled tubes of Spongeliomorpha and Thalassinoides en trenched in the mudstone, which form two char ac ter is tic ho ri - zons. Tubes were emplaced in semi-con sol i dated sub strate and filled with sand brought by storm-gen er ated bot tom cur - rents. The trace fos sils re veal fea tures typ i cal of Glossifungites ichnofacies as so ci ated firmgrounds, which re cord dis con ti nu ities in the strati graphi cal re cord, linked with a depositional hi a tus or con den sa tion and ero sion of the sea-floor.
The co in ci dence of these ho ri zons with early phases of re gional trans gres sions sug gests that they rep re sent transgressive sur faces of ero sion. Their lim ited spa tial ex tent prob a bly re sulted from vary ing in ten sity of ero sion, which lo cally scoured deeply down to al ready con sol i dated sub strate, whereas in other places ero sion was weaker or even ab sent, and thus it is not marked in the sed i men tary re cord there.
Key words: tu bu lar tempestite, shal low-ma rine mudstone, omis sion sur face, Lower Ju ras sic, Mid dle Ju ras sic, Silesian - -Kraków re gion.
INTRODUCTION
Tu bu lar tempestites are the open tubes pro duced by an i - mals bur row ing in a sta ble, stiff or firm sub strate, sub se quently filled with sed i ment trans ported by storm-gen er ated cur rents (Wanless et al., 1988). The in fill ing sed i ment is mas sive, usu - ally coarser than the host de posit and oth er wise may be not pre served in the suc ces sion from the lo cal depositional site be - cause of sed i ment by pass or swal low ing of the en tire storm lag by bur row sys tems (Tedesco and Wanless, 1991; Bromley, 1996; Gingras et al., 2007). The most com mon pro duc ers of such bur rows are crus ta ceans such as crabs and shrimps that con struct shafts with ap er tures ³1 cm in di am e ter, large enough to en able sed i ment eas ily to fall in side. Tak ing into ac count the elon gated shape and po si tion in the basal part of storm beds, tu bu lar tempestites may be mis taken for gut ter casts – the nar - row ero sional scours filled with coarse-grained sed i ment, which are the com mon con stit u ent of storm-in flu enced suc ces sions.
How ever, the lat ter struc tures re sult in whole from the storm pro cesses, whereas the for ma tion of tu bu lar tempestites be gins ear lier, dur ing the fair-weather pe ri ods, and only the fill ing is linked with storms. The ar range ment of tun nels as well as scratch marks ob served lo cally on their sur faces clearly sup port their biogenic or i gin.
For the first time, tu bu lar tempestites were de scribed by Wanless et al. (1988) from the shal low ma rine car bon ate Baha - ma Plat form, where they con sti tuted the dom i nant sed i men tary re cord of Hur ri cane Kate. Most of the coarse-grained sur face sed i ment, re worked by storm waves, was there en trapped by a net work of large Callianassa bur rows, caus ing that a thin sur ficial tempestite layer was dif fi cult to dis tin guish from the fair- weather de posit. Tedesco and Wanless (1991) showed that the re pet i tive ex ca va tion and sub se quent storm in fill ing of open bur rows might lead to gen er a tion of the new fab rics and re place ment fa cies.
These au thors sug gested that such sed i ments should oc cur in suc ces sions from var i ous en vi ron ments through out the Phane - rozoic. Ac tu ally, tu bu lar tempestites have been rec og nized in sev eral an cient de pos its, in car bon ates as well as in siliciclastics (e.g., Bann et al., 2004; Droser et al., 2004). Re lated struc tures with a rhyth mi cally lam i nated fill, re ferred to as tu bu lar tidalites, have been de scribed from intertidal and subtidal en vi ron ments (e.g., Gingras et al., 2007, 2012; Wetzel et al., 2014).
The oc cur rence of tu bu lar tempestites is es pe cially use ful in the case of bioturbated de pos its, in which pri mary sed i men tary struc tures have not been pre served. They are of ten the only ev - i dence for the pre vi ous ac tiv ity of storms, pro vid ing rel e vant in - for ma tion about the dy nam ics of sed i men tary en vi ron ment. The ho ri zons with tu bu lar tempestites are used in se quence stra tig - ra phy anal y sis, as they of ten ac com pany omis sion sur faces, re - cord ing syndepositional ero sion and re duced sed i men ta tion rate. These pro cesses are char ac ter is tic of an ini tial stage of trans gres sion and transgressive sys tem tract, dur ing which terrigenous sed i ment is mostly trapped in the coastal zone, and the shal low ma rine en vi ron ment be comes starved of sed i ment (Catuneanu et al., 2011).
* E-mail: Paulina.Leonowicz@uw.edu.pl
Received: March 19, 2015; accepted: July 22, 2015; first published online: August 31, 2015
The pres ent pa per ad dresses tu bu lar tempestites from the Lower and Mid dle Ju ras sic shal low ma rine mudstones, re ferred to as the Ciechocinek For ma tion and the Częstochowa Ore- Bear ing Clay For ma tion, which crop out in the Silesian-Kraków Up land in south ern Po land (Fig. 1). These sand-filled tubes were pre vi ously de scribed in stud ies con cern ing trace fos sils and ichnofabrics from these suc ces sions (Leonowicz, 2009, 2012), how ever, they were not in ter preted in re la tion to storm pro cesses.
GEOLOGICAL SETTING
Ju ras sic de pos its stud ied here crop out in an elon gated, NW–SE-ori ented belt, ex tend ing be tween Kraków and Wieluń (Fig. 1). They con sti tute part of the Silesian-Kraków Monocline con sti tuted by Perm ian and Me so zoic rocks, dip ping gently to - wards the NE. The mudstones of the Lower Ju ras sic Ciecho - cinek For ma tion and the Mid dle Ju ras sic Częstochowa Ore- Bear ing Clay For ma tion are ex posed in sev eral clay-pits. Tu bu - lar tempestites were found in two of them, lo cated in Kozłowice and Częstochowa (Fig. 1).
Perm ian and Me so zoic rocks from the Silesian-Kraków Up - land were de pos ited in a shal low epicontinental sea, called the Pol ish Ba sin (Dadlez, 1989), which was an east ern most arm of an ex ten sive Cen tral Eu ro pean Ba sin Sys tem (CEBS; Fig. 2).
The Pol ish Ba sin was a semi-en closed sea, sur rounded to the north, east and south-west by land. To the west and north-west
it was con nected with the CEBS, mainly through the North Ger - man and Dan ish bas ins (Dadlez, 1989; Pieńkowski, 2004). To the south-east a tem po rary con nec tion with the Tethyan Ocean through the East Carpathian Gate ex isted re peat edly (Dadlez and Kopik, 1975; Dayczak-Calikowska, 1997). Dur ing the Ju - ras sic these con nec tions served as sea ways for sev eral ma rine trans gres sions, ap proach ing from the west and north-west in the Early Ju ras sic (Pieńkowski, 2004) and prev a lently from the south-east in the Mid dle Ju ras sic (Dayczak-Calikowska, 1997).
The most com plete suc ces sion was de pos ited in the elon gated, NW–SE-ori ented ax ial zone, called the Mid-Pol ish Trough (MPT; Fig. 3), which was char ac ter ized by the max i mum sub si - dence through out the Me so zoic. Out side the MPT the suc ces - sion re veals sev eral hi a tuses and the thick ness de creases grad u ally to wards the north-east and south-west. In the Silesian -Kraków re gion it is re duced to a max i mum of 200 m for the Lower Ju ras sic and 300 m for the Mid dle Ju ras sic (Dayczak-Calikowska and Moryc, 1988; Deczkowski, 1997;
Feldman-Olszewska, 1997a, b).
LOWER JURASSIC
Dur ing the Early Ju ras sic, sed i men ta tion de vel oped mainly in ter res trial and re stricted nearshore en vi ron ments (Pień - kowski, 2004). The suc ces sion con sists of var i ous siliciclastic rocks, in clud ing sand stone, mudstone, claystone and gravel (Fig. 4A). Open-ma rine and brack ish con di tions de vel oped
Fig. 1A – geo log i cal map of the Silesian-Kraków Up land (af ter Dadlez et al., 2000, sim pli fied) and lo ca tion of the suc ces sions stud ied; B – area shown on map A
Fig. 2. Palaeo geo graphi cal maps of Eu rope A – in the Early Ju ras sic, B – in the Mid dle Ju ras sic (mod i fied af ter Ziegler, 1990) AM – Armori can Mas sif, BM – Bo he mian Mas sif, CEBS – Cen tral Eu ro pean Ba sin Sys tem, IM – Irish Mas sif,
LBM – Lon don-Brabant Mas sif, MCA – Meta-Carpathian Arc, RHB – Rockall-Hatton Bank, UH – Ukrai nian High
Fig. 3. Pol ish Ba sin dur ing the Early and Mid dle Ju ras sic and the lo ca tion of stud ied ex po sures A – Early Toarcian tenuicostatum chron (mod i fied af ter Dadlez, 1973; Pieńkowski, 2004);
B – Mid dle Bathonian bremeri chron (mod i fied af ter Feldman-Olszewska, 1998)
mainly in the MPT zone and ad ja cent ar eas dur ing Mid dle Hettangian, Early and Late Sinemurian, Early and Late Pliensba chian and Early Toarcian ma rine trans gres sions (Pień - kowski, 2004). The wid est ex tent of the sea was linked with the Early Toarcian trans gres sion (Fig. 3A), dated at the tenuico - statum and ear li est falciferum chrons (Pieńkowski, 2004). This trans gres sion is re corded by the muddy Ciechocinek For ma - tion, wide spread in the en tire Pol ish Ba sin. In the Silesian- Kraków re gion it is up to 70 m thick (Leonowicz, 2011). It rests on the Pliensbachian sandy Blanowice For ma tion (Fig. 4A) rep - re sent ing al lu vial, lac us trine and deltaic en vi ron ments, and is over lain by the Up per Toarcian sand-mud Borucice For ma tion of also al lu vial and lac us trine or i gin (Pieńkowski, 2004).
CHARACTERISTICS OF THE CIECHOCINEK FORMATION
The Ciechocinek For ma tion is com posed of ol ive-green, grey and wil low-green mudstone, claystone and siltstone with lenses and in ter ca la tions of fine-grained sand stone and sid er - ite bands (Fig. 4A, B). Sedimentological anal y ses pointed to de po si tion in a shal low ba sin, prev a lently <20 m deep, dis play - ing fea tures of a large shal low embayment with deltaic fa cies de vel oped in mar ginal parts (Pieńkowski, 2004). Well- pre - served sed i men tary struc tures oc cur ring through out the suc - ces sion in di cate that the de po si tion was strongly in flu enced by storms. The quiet back ground sed i men ta tion was re peat edly Fig. 4A – lithostratigraphy of the Lower Ju ras sic in the Silesian-Kraków re gion (af ter Kopik, 1998; Pieńkowski, 2004) and rep re sen - ta tive sec tion of the Pawłowice 40 bore hole. Bound aries of depositional se quences (IV–IX) and parasequences (VIIIa, b, c, d) ac - cord ing to Pieńkowski (2004). In ter val ex posed in Kozłowice is marked to the right; B – lithological log of the Ciechocinek For ma tion de pos its from the Kozłowice sec tion (af ter Leonowicz, 2011) and the lo ca tion of ho ri zon with tu bu lar tempestites, shown on C. Bound aries of parasequences VIIIb, c, d ac cord ing to Hesselbo and Pieńkowski (2011). Bound ary be tween parasequences a and b pro posed in this pa per co in cides with the ho ri zon with tu bu lar tempestites; C – two sandy ho ri zons sep a - rat ing dark grey and ol ive-green mudstone; the up per one con tains tu bu lar tempestites, rep re sented by sand-filled Spongelio - morpha tubes (some of them marked by ar rows)
in ter rupted by storm ep i sodes, dur ing which bot tom cur rents trans ported sand from the nearshore to dis tal set tings (Leo - nowicz, 2011). The sand was af ter wards re worked by waves and re dis trib uted on the sea-floor by wave-drift and wind-driven flows. In dis tal set tings, storm events were re - corded by small- scale sed i men tary struc tures ob served in mudstone, in clud ing:
– graded sand-silt streaks;
– graded se quences: trough cross-lam i nated silt – par al - lel-lam i nated silt – mas sive mud;
– small sandy lenses;
– interlaid mud-silt-sand heteroliths, stick ing in the mud (Leonowicz, 2011).
In prox i mal set tings, tempestites are rep re sented by sev eral centi metre thick sandy lay ers and sev eral decimetre thick sandy pack ets, show ing var i ous types of sed i men tary struc - tures, in clud ing wavy-, flaser-, rip ple-, par al lel- and cross-bed - ding as well as rare hummocky cross-strat i fi ca tion (HCS). The ripplemarks ob served in wavy- and rip ple-bed ded sand stones com monly re veal fea tures typ i cal of wave or i gin. In the by pass zone, sandy gut ter casts formed (Leonowicz, 2011).
The scar city of ben thic fauna, the im pov er ished trace fos sil as so ci a tion and the geo chem i cal char ac ter is tics point to the brack ish char ac ter of the ba sin (Pieńkowski, 2004; Leonowicz, 2005, 2007, 2009). The lower part of the Ciechocinek For ma - tion re cords a pro gres sive trans gres sion and is prev a lently de - vel oped as dark grey mudstone con tain ing ma rine dinofla - gellate cysts, foraminiferal lin ings and a rel a tively di verse trace fos sil as so ci a tion, in clud ing Planolites, Palaeophycus, Helmin - thopsis, Gyrochorte, Protovirgularia, Spongeliomorpha and Diplo craterion, as well as com mon py rite min er ali sa tion (Leo - nowicz, 2009, 2011). The up per part, which is com posed of green ish de pos its with a strongly im pov er ished trace fos sil as - so ci a tion (mainly Planolites) and phyl lo pods Estheria, re flects a grad ual de cline in wa ter sa lin ity dur ing a sea level highstand and re gres sion (Leonowicz, 2011).
TUBULAR TEMPESTITES FROM THE CIECHOCINEK FORMATION
De scrip tion: sand-filled tun nels of Spongeliomorpha isp.
are pre served as endichnia within mudstone (Fig. 4C). The tun - nels are up to 2.5 cm thick, hor i zon tal or subhorizontal, and branch at acute an gle (Fig. 5A). On the lower and side sur faces of the bur row casts, elon gated scratch marks oc cur (Fig. 5B).
The in fill ing con sists of light grey fine quartz sand (Fig. 6A) and is structureless or, rarely, con tains thin wavy clay lamina (Fig.
5C), sug gest ing two stages of bur row fill ing.
Oc cur rence: The ho ri zon with Spongeliomorpha oc curs in the low er most part of the ca. 36 m thick sec tion ex posed in the Kozłowice clay-pit (Fig. 1), which is dated at the tenuicostatum zone (Barski and Leonowicz, 2002). Most of this sec tion con - sists of ol ive-green claystone and mudstone with sev eral thin (up to 10 cm) in ter ca la tions of sand stone and two thick (2.2 and 3.5 m) sandy com plexes (Fig. 4B). At the bot tom, dark grey mudstone with com mon framboidal py rite oc curs (Leonowicz, 2011). This dark grey mudstone is sep a rated from the over ly ing ol ive-green de posit by two sandy ho ri zons (Fig. 4B, C). The lower one con sists of a strongly bioturbated sand stone bed, ca. 5 cm thick. The up per one, ca. 10 cm thick, con tains sand-filled tun nels of Spongeliomorpha de scribed above, which are ac com pa nied by thin sandy laminae and lenses dis persed in the mudstone. Lower and mid dle parts of
the sec tion con tain a rel a tively di verse trace fos sil as so ci a tion and ma rine dinoflagellate cysts point ing to their ma rine or i gin (Leonowicz, 2009, 2011).
MIDDLE JURASSIC
The Mid dle Ju ras sic was a time of pro gres sive ma rine trans gres sion, which be gan in the Aalenian (Dayczak- Caliko - wska and Moryc, 1988) and was in ter rupted by sev eral short - -lived re gres sions and stillstand pe ri ods. The suc ces sion con - sists of var i ous siliciclastic rocks with the prev a lence of dark grey mudstone. Ini tially, the sea oc cu pied only the MPT, but from the Early Bajocian it grad u ally spread out side this zone, ex tend ing to the north-east and south-west (Feldman- Olsze - wska, 1998). In the Silesian-Kraków re gion the be gin ning of ma rine sed i men ta tion is re corded by sandy de pos its of the Early Bajocian Kościelisko Beds (Kopik, 1998; Fig. 7A). The de - vel op ment of the trans gres sion (Fig. 3B) led to de po si tion of a thick (up to 200 m) muddy com plex re ferred to as the Często - chowa Ore-Bear ing Clay For ma tion, span ning the Up per Bajo - cian to Up per Bathonian (garantiana–dis cus zones; Kopik, 1998; Matyja and Wierzbowski, 2000, 2006; Barski et al., 2004).
The Częstochowa Ore-Bear ing Clay For ma tion is over lain by con densed Callovian de pos its (Fig. 7A), which in turn pass up - wards into Oxfordian lime stones re cord ing fur ther ex pan sion of the sea (Kopik, 1997).
CHARACTERISTICS
OF THE CZĘSTOCHOWA ORE-BEARING CLAY FORMATION
The Częstochowa Ore-Bear ing Clay For ma tion is com - posed of dark grey or ganic-rich cal car e ous mudstone with ho ri - zons of sid er ite and cal car e ous con cre tions and sid er ite bands (Fig. 7A, B). These de pos its, known also as the ore-bear ing clay, are de vel oped as two fa cies va ri et ies. The first one is rep - re sented by bioturbated mudstone con tain ing com mon ben thic fauna and a mod er ately di verse trace fos sil as so ci a tion. The sec ond one con sists of lam i nated de posit with rare ben thic fauna and an im pov er ished trace fos sil suite (Leonowicz, 2012, 2013). Sedimentological anal y ses pointed to de po si tion in a shal low-ma rine ba sin, sev eral tens of metres deep, but shallowing to less than 20 m in some pe ri ods (Leonowicz, 2015). The sea bot tom was mostly be low storm wave base, how ever, sed i men ta tion was strongly in flu enced by ep i sodic high-en ergy con di tions. Sed i men tary struc tures pre served in lam i nated de pos its in clude thin silt/sand laminae, bed ding - -plane ac cu mu la tions of shell de bris, small and me dium silt- sand lenses as well as silt-, sand- and shell-de bris-rich lev els (Leonowicz, 2013, 2015). They re cord ac tiv ity of bot tom cur - rents that re dis trib uted sed i ment from shal lower ar eas and in - ter mit tently re worked de pos ited ma te rial. Prior to de po si tion, ero sion of the sea-floor of ten oc curred as re corded by com mon ero sional sur faces and oc ca sional pro nounced scours. The cur rents were most prob a bly gen er ated by storms, al though an or i gin linked with tidal pro cesses was also con sid ered (Leono - wicz, 2015). The thick ness and amount of event laminae de - pended on the in ten sity of storms and the dis tance from the shore line, which changed with time. Based on the sand, silt and clay con tent of the mudstone, Leonowicz (2015) dis tin guished 7 transgressive-re gres sive cy cles within this suc ces sion, which fairly well-match the cy cles known from cen tral Po land (Pień - kowski et al., 2008).
Bioturbated mudstone is rich in ben thic fauna rep re sented by bi valves, gas tro pods, brachi o pods, sca pho pods, fora - minifers and echinoderms (Gedl et al., 2012). The trace fos sil suite in cludes Chondrites, Trichichnus, Palaeophycus, Plano - lites, Protovirgularia, Rosselia?, Schaubcylindrichnus, Taeni - dium, cf. Tasselia and Thalassinoides as well as some un de ter - mined pyritized bur rows. Di ver sity of ben thic fauna and trace fos sils changes in the ver ti cal suc ces sion as well as lat er ally, show ing that the con di tions on the sea-floor, such as ox y gen a - tion and sed i men ta tion rate, var ied sig nif i cantly.
TUBULAR TEMPESTITES FROM THE CZĘSTOCHOWA ORE-BEARING CLAY FORMATION
De scrip tion: sand-filled tun nels of Thalassinoides isp. are pre served as endichnia within a clayey sid er ite band (Fig. 5D, 7C). The tun nels are up to 4 cm thick, slightly flat tened, and form a 3-di men sional branch ing sys tem. They are filled with structureless light grey, very fine quartz sand and silt (Fig. 5D).
The tun nels were ob served only in cross-sec tion and the re lief of bur row walls is un known, how ever, they seem to be smooth and de void of scratch marks.
Fig. 5. Tu bu lar tempestites from the Ciechocinek For ma tion (A–C) and the Częstochowa Ore-Bear ing Clay For ma tion (D)
A – frag ment of Spongeliomorpha tube with vis i ble Y-shaped branch ing, view on the up per sur face; B – lower sur - face of bur row cast with elon gated scratch marks; C – cross-sec tion of bur row in fill ing, thin wavy laminae of clay is vis i ble in the mid dle; D – fine sand-filled Thalassinoides tun nel pre served within clayey sid er ite; branch ing of tun nel is vis i ble in the up per right; A, B, D – scale bar is in centi metres, C – scale bar is 1 cm
Fig. 6. The fill ing of Spongeliomorpha tube (A) and storm-event sand stone bed (B) in thin sec tion The grain frame work in both sam ples is dom i nated by quartz; on A quartz grains are ce mented by sid er ite;
Kozłowice out crop, crossed nicols, scale bar is 1 mm
Fig. 7A – stra tig ra phy of Mid dle Ju ras sic de pos its from the Silesian-Kraków re gion (af ter Kopik, 1998; Matyja and Wierzbowski, 2000, 2006; Barski et al., 2004) and rep re sen ta tive sec tion of the Zrębice 33-BN bore hole (stra tig ra phy af ter Kopik, 1998). B – lithological log of the Częstochowa Ore-Bear ing Clay For ma tion de pos its from the Częstochowa-Gnaszyn sec tion (af ter Leonowicz, 2015) and the lo ca tion of ho ri zon with tu bu lar tempestites, shown on C. Transgressive-re gres sive cy cles af ter Leonowicz (2015). Cor rected R4/T5 bound ary falls on the ho ri zon with tu bu lar tempestites; C – tu bu lar tempestite rep re sented by a sand-filled Thalassinoides tun nel (ar row), photo by A. Uchman
Oc cur rence: the ho ri zon with Thalassinoides oc curs in the mid dle part of the ca. 32 m thick sec tion ex posed in the Ganszyn clay-pit, sit u ated in the west ern sub urb of Często chowa (Fig. 1).
This sec tion con sists of dark grey, cal car e ous mudstone with sev eral ho ri zons of sid er ite con cre tions num bered N–S, and one sid er ite band marked as ho ri zon O (Fig. 7B). The mudstone is strongly bioturbated. Be sides a few silt-, sand- and shell-de - bris-rich lev els oc cur ring in the lower half of the suc ces sion, it re - veals only rel ics of fine hor i zon tal lam i na tion and rare small sandy lenses. In the mid dle and up per parts of the sec tion, ammonites com monly oc cur sug gest ing a de creased sed i men - ta tion rate. Sand-filled tun nels of Thalassino ides de scribed above oc cur in sid er ite level O (Fig. 7B, C), within the in ter val dated at the morrisi zone (Matyja and Wierz bowski, 2006).
INTERPRETATION AND DISCUSSION
The struc tures de scribed above were pro duced in an en vi - ron ment sig nif i cantly af fected by storms. The im por tant share of storm pro cesses in de po si tion of stud ied mudstones is con - firmed by the com mon oc cur rence of sed i men tary struc tures as cribed to storm or i gin and was al ready pos tu lated in ear lier stud ies (Pieńkowski, 2004; Leonowicz, 2011, 2013, 2015). In mudstone from Kozłowice, storm de pos its are well-pre served and rep re sented by var i ous sand and silt ac cu mu la tions, rang - ing from thin laminae formed in a dis tal lo ca tion to thick sand ac - cu mu la tions de pos ited in a prox i mal set ting. Gut ter casts, wave rip ples, HCS and cross-bed ded sand stone beds ob served within them re cord pro cesses typ i cally as so ci ated with storms, in clud ing syndepositional ero sion of the sea-floor, bedload trans port of sed i ment by bot tom cur rents and sub se quent wave re work ing of de pos its (Leonowicz, 2011). Sand-filled Spon - geliomorpha tubes oc cur in one ho ri zon with thin sandy laminae and lenses that rep re sent iso lated starved rip ples car ried on the muddy sea-floor by storm-gen er ated trac tion cur rents. The ma - te rial fill ing the tubes is sim i lar in com po si tion to that form ing sandy lenses and storm beds (Fig. 6), and hence it points to their sim i lar or i gin. Mas sive struc ture of the fill in di cates its pas - sive char ac ter. This sug gests that the sand mi grat ing on the sed i ment sur face was si mul ta neously trapped by aban doned bur rows open to the sea-floor. Thus, the fill of Spongeliomorpha is in ter preted as tu bu lar tempestite. The tube fill rep re sents very likely a sin gle storm event be cause of its prev a lent mas sive ap - pear ance and lack of in ter nal lam i na tion. How ever, in some cases, it can re cord also two or more storms, as is sug gested by thin clayey lamina ob served in the sandy fill.
In the case of mudstone at Częstochowa, the en vi ron men - tal in ter pre ta tion is im peded by its strong bioturbation, which oblit er ates the pri mary fab ric. How ever, the anal y sis of rel ics of sed i men tary struc tures and their com par i son with well-pre - served pri mary lam i na tion from ore-bear ing mudstone from other lo cal i ties has al lowed in fer ring a sig nif i cant role of storms dur ing de po si tion of the suc ces sion (Leonowicz, 2012, 2015).
This con clu sion was sup ported by the oc cur rence of few un dis - torted, rel a tively thick ac cu mu la tions of fine sand and shell de - bris, in ter preted as storm event de pos its (Leonowicz, 2015).
The sand-filled tubes of Thalassinoides pro vide an other strong ar gu ment for the key im por tance of storms, con tra dict ing al ter - na tive hy poth e ses re fer ring to tidal pro cesses (Leonowicz, 2015). The structureless char ac ter of the fill al lows in ter pret ing it as tu bu lar tempestite, sim i larly as Spongeliomorpha de - scribed above. Tu bu lar tidalites, in turn, shall ex hibit a rhyth mi - cally lay ered fill, re flect ing cy clic char ac ter of tides (Gingras et al., 2007; Wetzel et al., 2014). The ma te rial pre served within
the bur rows pro vides valu able in for ma tion about the pre sumed com po si tion of storm de pos its, sup port ing the as sump tion – es - sen tial for in ter pre ta tion of transgressive-re gres sive cy cles – that the sand dis persed within the mudstone mostly came from the storm event ac cu mu la tions (Leonowicz, 2015).
Tu bu lar tempestites pro vide also im por tant in for ma tion about the char ac ter of the sub strate and the course of sed i men - ta tion. In sub aque ous en vi ron ments un der nor mal con di tions, the an i mals con struct open tubes in soft sed i ment and have to re in force them by par ti cles or mu cus to pre vent col lapse (Bromley, 1996). As a re sult, bur row mar gins are ac cen tu ated by dis tinct lin ing or a thick wall, dif fer ing in com po si tion or pack - ing from the sur round ing sed i ment. Aban doned tubes are suc - ces sively filled with sed i ment fall ing in from the bot tom and the fill is usu ally com posed of ma te rial sim i lar to the host de posit. In de pos its stud ied, the bound aries of the trace fos sils are sharp but de void of lin ing that in di cates em place ment in semi-con sol i - dated sub strate (e.g., Wetzel and Uchman, 1998). The ex te rior of Mid dle Ju ras sic Thalassinoides was not ob served, thus it can be only in ferred that the sub strate was at least stiff. The Lower Ju ras sic Spongeliomorpha re veals dis tinct scratch marks on the sur face, which im plies firm char ac ter of the bot tom (Wetzel and Uchman, 1998). The sandy infill of these trace fos sils dif - fers from the sur round ing mud, in di cat ing that they were not con tin u ously filled with the fine-grained ma te rial, ac cu mu lat ing through out the bot tom but with the sed i ment pe ri od i cally by - pass ing the depositional site. This fea ture to gether with a stiff to firm char ac ter of the sub strate im plies a depositional hi a tus or con den sa tion com bined with ero sion of the sea-floor that led to ex po si tion of con sol i dated sub strate prior to the for ma tion and fill of the tubes. Such char ac ter of the trace fos sils al lows clas si - fy ing them to sub strate con trolled Glossifungites ichnofacies (cf. Leonowicz, 2009), which is a re li able in di ca tor of a dis con ti - nu ity in the strati graphic re cord.
Dis con ti nu ities ac cen tu ated by a Glossifungites suite of trace fos sils can form in dif fer ent ways (Pem ber ton et al., 2004;
MacEachern et al., 2007), rang ing from stratigraphically im por - tant allocyclic events (e.g., flood ing sur faces, amal gam ated se - quence bound aries or transgressive sur faces of ero sion) to autocyclic dis con ti nu ities (e.g., form ing in pe ri od i cally ex posed intertidal flats or mar gins of tidal chan nels) and dif fer ac cord - ingly. Both stud ied firmground ho ri zons de vel oped dur ing an early phase of trans gres sions. The ho ri zon from Kozłowice oc - curs in the low er most part of the Ciechocinek For ma tion suc - ces sion, re cord ing the be gin ning of re gional trans gres sion pro - nounced in the en tire Pol ish Ba sin (depositional se quence VIII, parasequence VIIIb in Pieńkowski, 2004) as well as in other bas ins of the CEBS (cf. Hal lam, 1988, 2001; Pieńkowski et al., 2008). The firmground from Częstochowa formed in the early morrisi chron, dur ing the early phase of trans gres sion marked in the en tire Pol ish Ba sin (T5 in Silesian-Kraków re gion – Leo - nowicz, 2015, T6 in cen tral Po land – Pieńkowski et al., 2008:
fig. 14.18) and cor re lat ing with the be gin ning of a long-last ing sea level rise on the eustatic curve of Hal lam (1988). Tak ing into ac count the po si tion of the stud ied firmgrounds, both ho ri - zons are in ter preted as omis sion sur faces linked with rapid trans gres sions. Some doubts may arise from the lack of equiv a - lent ho ri zons in other sec tions from the Silesian-Kraków re gion (Leonowicz, 2009, 2011 and own un pub lished ob ser va tions con cern ing Mid dle Ju ras sic strata), as dis con ti nu ities re cord ing events of a re gional ex tent shall have a wide spa tial oc cur rence.
The pos si ble ex pla na tion is that the win now ing ca pac ity of bot - tom cur rents var ied within the ba sin and only lo cally it ex ceeded sed i men ta tion rates, re sult ing in the de vel op ment of lo cal firmgrounds. In the case of the Mid dle Ju ras sic, such dif fer en ti - a tion of the bot tom cir cu la tion was al ready pos tu lated to ex plain
the lo cal ex tent of ho ri zons with hi a tus con cre tions (Leonowicz, 2015) and var i ous thick nesses of de pos its (e.g., Dadlez, 1994;
Feldman-Olszewska, 1997b; Barski, 1999). It was sug gested that this dif fer en ti a tion might be linked with the oc cur rence of tem po ral swells and de pres sions on the sea-floor, re sult ing from synsedimentary tec tonic move ments (Leonowicz, 2013, 2015). A mor pho log i cal dif fer en ti a tion within the CEBS by tem - po rary swells and de pres sions dur ing the Ju ras sic has been de - scribed also from other ar eas (e.g., Wetzel and Allia, 2000;
Wetzel et al., 2003).
In this con text, it is likely that the be gin ning of trans gres sion T5 in the Silesian-Kraków re gion falls on sid er ite level O, con - tain ing tu bu lar tempestites, not 1.5 m be low it, as it was placed pre vi ously (cf. Leonowicz, 2015). The low net sed i men ta tion rate, which led to the for ma tion of this firmground, was prob a bly linked with re cur rent syndepositional ero sion of the bot tom dur - ing the pas sage of the depositional site through the by pass zone (Leonowicz, 2015). Re duced ac cu mu la tion pro longed also dur ing the whole morrisi chron and, to a lesser de gree, dur - ing the bremeri chron, as is sug gested by com mon ammonite oc cur rences. The firmground from Kozłowice, which oc curs within ma rine de pos its rep re sented by dark grey mudstone with framboidal py rite and ol ive-green mudstone with a rel a tively di - verse trace fos sil as so ci a tion, prob a bly re cords the prog ress of trans gres sion in ter rupted by a short-last ing re gres sive ep i sode, marked by an un der ly ing strongly bioturbated sandy ho ri zon.
This firmground may con sti tute the flood ing sur face of parasequence VIIIb in the scheme pro posed by Hesselbo and Pieńkowski (2011).
SUMMARY AND CONCLUSIONS
Tu bu lar tempestites oc cur in Lower and Mid dle Ju ras sic mudstones in south ern Po land in two ho ri zons within the Cie -
cho cinek For ma tion and the Częstochowa Ore-Bear ing Clay For ma tion from the Silesian-Kraków re gion. They are rep re - sented by large sand-filled tubes of Spongeliomorpha and Thalassinoides. The sed i ment fill ing the bur rows is sim i lar in com po si tion to storm event beds, im ply ing that it was de rived by storm-gen er ated bot tom cur rents. The struc tures ev i dence a pe ri od i cal in flu ence of high-en ergy pro cesses dur ing mudstone de po si tion and are es pe cially valu able in en vi ron men tal in ter - pre ta tion of bioturbated mudstone, the pri mary fab ric of which was oblit er ated by bur row ing an i mals.
The char ac ter of bur row bound aries in di cates that they were emplaced in semi-con sol i dated sub strate. The pas sive na ture of the fill shows that tun nels re mained open to the sea-floor af ter the an i mals left their do mi ciles. These fea tures are char ac ter is tic of Glossifungites ichnofacies, which is as so ci ated with the firm sub - strate re cord ing a depositional hi a tus com bined with ero sional ex hu ma tion of com pacted mud. Both de scribed ho ri zons cor re - late with ini tial phases of trans gres sions pro nounced in the en tire Pol ish Ba sin: the ho ri zon with Spongeliomorpha de vel oped in the Early Toarcian tenuicostatum chron, whereas the ho ri zon with Thalassinoides – in the Mid dle Bathonian morrisi chron. They prob a bly rep re sent transgressive sur faces of ero sion, how ever, their lim ited ex tent shows that the ero sion ex humed con sol i dated sub strate only lo cally, whereas in other lo ca tions it was shal lower and is now un de tect able in the rock re cord.
Ac knowl edge ments. The au thor ess would like to thank P. Roniewicz and A. Uchman for in spir ing dis cus sion dur ing a joint fieldtrip. I also thank A. Wetzel and the anon y mous re - viewer for their con struc tive com ments and use ful re marks, which helped me to im prove the fi nal ver sion of the manu script.
The man age ments of brickyards Cerpol-Kozłowice S.A. and Wienerberger Gnaszyn in Częstochowa are thanked for pro vid - ing ac cess to their work ings. The re search was fi nanced by the In sti tute of Ge ol ogy, Uni ver sity of War saw.
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