Ptychoplasma conica isp. nov. — a new bi valve lo co mo tion trace fos sil from the Lower Ju ras sic (Hettangian) al lu vial sed i ments of Sołtyków,
Holy Cross Moun tains, Po land
Grzegorz PIEŃKOWSKI and Al fred UCHMAN
Pieńkowski G. and Uchman A. (2009) — Ptychoplasma conica isp. nov. — a new bi valve lo co mo tion trace fos sil from the Lower Ju ras - sic (Hettangian) al lu vial sed i ments of Sołtyków, Holy Cross Moun tains, Po land. Geol. Quart., 53 (4): 397–406. Warszawa.
A new lo co mo tion (repichnion) trace fos sil, Ptychoplasma conica isp. nov., which is com posed of chains of hypichnial mounds, is de - scribed from Hettangian al lu vial sed i ments in Cen tral Po land. Its oc cur rence is lim ited to amal gam ated cre vasse sand stones. The trace fos sil is as so ci ated with fresh wa ter bi valves be long ing prob a bly to Unionidae. This trace fos sil re flects rhyth mic (?di ur nal) move ment of the tracemaker in ac cor dance with the di rec tion of flow in the cre vasse chan nel, where the for ward move ment took place in the shal low part of a sand stone layer and was in ter rupted by rest ing ep i sodes in deeper sed i ment layer along the mud-sand in ter face. Ep i sodic flood events forced bi valves to pro duce es cape struc tures, mov ing from deeper (pre vi ous) to up per (later) lev els of lat eral move ments. Some ver ti cal bur rows with bi valve body fos sils pre served at the bot tom sug gest a taphonomic burial. P. conica ranges from Late Tri as sic to Hettangian.
Grzegorz Pieńkowski, Pol ish Geo log i cal In sti tute–Na tional Re search In sti tute, Rakowiecka 4, PL-00-975 Warszawa, Po land; e-mail:
grzegorz.pieńkowski@pgi.gov.pl; 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: al fred.uchman@uj.edu.pl (re ceived: May 07, 2009; ac cepted: Sep tem ber 16, 2009).
Key words: ichnofossils, ichnotaxonomy, repichnia, cre vasse splays, Hettangian.
INTRODUCTION
Bi valves are com mon tracemakers both in ma rine and non-ma rine fos sil and re cent en vi ron ments. One of the com - mon est of bi valve trace fos sils is Lockeia James, 1879, which is a rest ing trace (cubichnion), pre served mostly as amygdaloid hypichnial mounds. No less com mon is Protovirgularia M’Coy, 1850, a lo co mo tion (repichnion) trail, pre served mostly as hypichnial ridges with chev ron ribs (e.g., Seilacher and Seilacher, 1994; Mángano et al., 1998). The chev ron ribs are traces of a bi valve’s cleft foot, which is an chored in the sed - i ment dur ing lo co mo tion (e.g., Seilacher and Seilacher, 1994).
Much less is known about lo co mo tion trace fos sils re lated to bi valves hav ing a non-cleft (wedge) foot. These be long to the ichnogenus Ptychoplasma Fenton and Fenton, 1937, which is typ i fied by Ptychoplasma excelsa Fenton and Fenton, 1937 from the Car bon if er ous of Texas. This trace fos sil is al most un - known. Häntzschel (1975, p. W187) placed it among “Un rec -
og nized and Un rec og niz able Gen era”, mostly be cause its type ma te rial was not avail able for him. The ma te rial was ex am ined by Rindsberg (pers. comm., 2007), who de scribed some trace fos sils from the Car bon if er ous of Al a bama un der this ichnogenus (Rindsberg, 1994). It is rec og nized that Hostynichnium Plička et Siráňova, 1989 and Tuberculichnus vagans Książkiewicz, 1977 be long to this ichnogenus (Mikuláš, Rindsberg and Uchman, sub mit ted).
All of the hith erto known ichnotaxa oc cur in ma rine en vi - ron ments. In this pa per, we de scribe a new ichnospecies of Ptychoplasma, which was found in non-ma rine Early Ju ras sic (Hettangian) sed i ments at Sołtyków in Cen tral Po land. Its mor - pho log i cal fea tures are dif fer ent from known Ptychoplasma ichnospecies, but share the same prin ci ples of a lo co mo tive, un - du lat ing trail.
In ver te brate trace fos sils from Sołtyków, in clud ing those pro duced by bi valves, have been ex ten sively de scribed by Pieńkowski and Niedźwiedzki (2009). How ever, one of these ichnofossils needs new def i ni tion and de tailed be hav ioural char ac ter is tics, which is the aim of the pres ent pa per.
GEOLOGICAL SETTING
The Sołtyków ex po sure is an old, long-aban doned clay pit.
This ex po sure be came known as a clas sic out crop of Early Ju ras - sic al lu vial plain de pos its, be long ing to the con ti nen tal Zagaje For ma tion and the low er most Ju ras sic depositional se quence I (Pieńkowski and Gierliński, 1987; Pieńkowski, 1998, 2004;
Figs. 1–3). Plant re mains (Wcisło-Luraniec, 1991; Ziaja, 2006) point to the Hettangian (Lias al pha 1-2), and the se quence strati - graphic cor re la tion (Pieńkowski, 2004) al lows its age range to be nar rowed to the Early Hettangian (Planorbis chron — or the ear - lier, up to date still in for mal, Tilmanni chron). Re cently, the conchostracan Bulbilimnadia killiani Kozur et Weems 2005, was found at Sołtyków, point ing to the ear li est Hettangian (H.
Kozur, pers. comm., 2009). The plant fos sils and palaeosol lev - els are very abun dant in Sołtyków. The list of plants in cludes Neocalamites, the matoniacean, osmundacean and other in de ter - mi nate ferns, as well as pteridosperms, benettitaleans and co ni - fers (Wcisło-Luraniec, 1991; Ziaja, 2006). Other fos sils that oc - cur in Sołtyków are rep re sented by a unionid fresh wa ter bi valve as sem blage, in sect re mains (Wegierek and Zherikhin, 1997), fresh wa ter ostracodes, scales of palaeoniscid fish and the above-men tioned conchostracans. The Sołtyków ex po sure is a well known Early Ju ras sic tracksite with nu mer ous di no saur foot prints, mainly left by theropods and sauro pods, and early mam ma lian foot prints (Pieńkowski and Gierliński, 1987;
Gierliński and Pieńkowski, 1999; Gierliński et al., 2001, 2004).
A di no saur nest ing ground has also been de scribed (Pieńkowski, 1998). Re cently, the Sołtyków ex po sure has been de clared a nat - u ral re serve.
Ac cord ing to Miall (1977) and his plan-view mor phol ogy clas si fi ca tion, the types of rivers are con trolled chiefly by wa ter dis charge, sed i ment load, chan nel slope, and type of veg e ta - tion. Based on that prin ci ple, four types of rivers were dis tin - guished: braided, me an der ing, straight and anastomosing.
Anastomosing/avul sion pat terns are most com mon on very low-gra di ent al lu vial plains, where rate of flow is low and banks con sist of muddy, co he sive sed i ment or are highly veg e - tated (Nanson and Croke, 1992; Em ery and Myers, 1996). A rel a tively thick and in di vid u al ized pack age of lac us trine de pos - its (dark grey to black, lam i nated or of mas sive mudstones with plant-root ho ri zons as so ci ated with dis tal cre vasse in ter ca la - tions (Figs. 2 and 3) points to some per ma nency of the lake/swamp area dur ing de po si tion of the sed i ments and to a low-gra di ent, low-en ergy al lu vial plain. Likely, fine bed-load to sus pended-load sed i ment was de pos ited in the floodplain as
“overbank” sed i ments dur ing floods and as a “nor mal” sed i - men ta tion in a lac us trine en vi ron ment. It should be noted, that Aslan and Autin (1999) be lieve that avul sion, rather than sim - ple overbank de po si tion, con trib utes to the con struc tion of fine-grained floodplains to a greater de gree than gen er ally re - cog nised. The fact that the type 2 cre vasse (delta-like) ap pears in the mid dle part of the sec tion (Fig. 2) in di cates a grow ing aggradational/avul sion ten dency, as so ci ated with a much higher wa ter ta ble (Aslan and Autin, 1999). The depth of this lake en vi ron ment can be es ti mated at 0 to a few metres, judg ing
from the com mon plant roots and stems, par tic u larly those of horse tails (which might have grown un der shal low wa ter) and traces of swim ming theropod di no saurs scratch ing the bot tom (Gierliński et al., 2004). This points to a wa ter depth of about 2 m, judg ing from a length of legs of Dilophosaurus, the al - leged pro ducer of these trace fos sils.
On the other hand, the pres ence of in di vid u al ized chan nel de pos its with lat er ally-accreted bed ding in sand stones and as so - ci ated cre vasse splays point to the ex is tence of pe ri ods of more in tense drain age and higher en ergy of cur rents. Gen er ally, the Sołtyków ex po sure fits the mixed char ac ter be tween an avul - sion-con trolled (crevassing-anastomosing) flu vial sed i men ta tion model (Farrel, 2001) and a me an der ing model with the pres ence of high-sin u os ity/me an der ing streams (Pień kowski, 2004).
Im por tantly, chan nel lithofacies (me dium to poorly sorted, trough-cross bed ded, lat er ally accreted sand stone) are com - monly un der lain by both type 1 (sharply based, with the sud den in cur sion of sed i ment-laden wa ter and sed i ment trans port per - pen dic u lar to the main chan nel) and type 2 (un con fined flow with the basinward progradation of a mi nor mouth bar/cre vasse chan nel cou plet) cre vasses (Farrel, 2001). This points to im por - tance of crevassing (= flood ing) pro cesses in ini ti at ing new courses of chan nels, which is par tic u larly char ac ter is tic of the anastomosing pat tern. Ac cord ing to the avul sion model (Farrel, 2001), an ini tial avul sion stage is ac com plished pre dom i nantly by the de vel op ment of cre vasse splay com plexes that cause the en large ment of new chan nels and aban don ment of old ones.
Cre vasse splays de vel oped at the lo cal breaches in the lev ees, which fun nelled the flow from the chan nel dur ing the flood and pro vided con duits for sus pended- and bed-load sed i ment dis - persal into near-chan nel (of ten sub-aquatic — lac us trine) por - tions of the floodplain (Gal lo way and Hobday, 1996). Cre vasse splays at Sołtyków are typ i cal sed i men tary “gar bage piles”, ac - cu mu lat ing rap idly large amounts of plant de bris and mud clasts. They dif fer from the as so ci ated chan nel subenvironment de pos its in hav ing smaller grain sizes and unit thick nesses.
Channelised cre vasse splays show a mul ti stage in fill ing with re ac ti va tion sur faces (Fig. 3), which in di cates that the lo cal breaches in the lev ees oc cu pied the same po si tion for some time, fun nel ling the flow in much the same place dur ing many flood events.
Cre vasse splay suben vi ron ment was par tic u larly fa vour - able for pres er va tion of the di no saur foot prints (Pieńkowski and Gierliński, 1987; Gierliński and Pieńkowski, 1999;
Gierliński et al., 2001). In ver te brate bur rows (Pieńkowski and Niedźwiedzki, 2009) con cen trate mostly also in cre vasse splay de pos its, and to a lesser ex tent in floodplain de pos its and levee de pos its; the lat ter are not very com mon at Sołtyków be cause levee de pos its are prone to sub se quent ero sion. Non-ma rine trace fos sils have been re cently de scribed by Pieńkowski and Niedźwiedzki (2009) and they com prise forms be long ing to the
?Coprinisphaera, Scoyenia and Mermia ichnofacies (us ing of the term Coprinisphaera ichnofacies for this sec tion and for Ju - ras sic de pos its in gen eral, how ever, is a mat ter of de bate). Bi - valve trace fos sils have been also de scribed in that pa per, al - though the pe cu liar bi valve lo co mo tion trail de scribed herein needs more de tailed char ac ter iza tion.
398 Grzegorz Pieńkowski and Alfred Uchman
SYSTEMATIC PART
Ichnogenus Ptychoplasma Fenton and Fenton, 1937 Type ichnospecies Ptychoplasma excelsa
Fenton and Fenton, 1937
D i a g n o s i s. — In hypichnial as pect, nearly smooth, un du lat ing, con tin u ous to dis con tin u ous subhor i zon tal ridges that dis play a char ac ter is ti cally amygdaloid, carinate or blocky cross-sec tion, lit tle or no chev ron sculp ture, and com monly a straight, wind ing, ir reg u larly me an der ing or loop ing course (Mikuláš, Rindsberg and Uchman, sub mit ted).
R e m a r k s. — Ptychoplasma dif fers from Protovirgularia M`Coy, 1850 by its un du la tory re lief and only lo cal, faint chev ron ribs, if pres ent at all. Lockeia James, 1879 is lim ited only to sin gle mounds.
Fig. 1. Hettangian bas ins of Po land and NW Eu rope with syn thetic pro file of the Lower Ju ras sic in the Holy Cross Moun tains re gion and lo ca tion of the Sołtyków out crop
Lithoformations: Z.F. — Zagaje Fm., S.F. — Skłoby Fm., P.O.F. — Przysucha Ore-Bear ing Fm., O.F. — Ostrowiec Fm., G.F. — Gielniów Fm., D.F. — Drzewica Fm., C.F. — Ciechocinek Fm., B.F. — Borucice Fm.;
source ar eas left blank; af ter Pieńkowski, 2004 (sim pli fied)
400 Grzegorz Pieńkowski and Alfred Uchman
Fig. 2. Sedimentological log of the Solłtyków out crop (af ter Pieńkowski 2004, emended) with in di ca tion of the cre vasse de pos its bear ing Ptychoplasma conica isp. nov.
Ptychoplasma conica isp. nov.
(Figs. 3–6)
1949, einzeilige Reihenhöcker-Spur – Linck, 666–669, pl. 8, figs. 1–2.
1955, Unbenannte Kriechspur einer Muschel – Seilacher, fig. 5 (31) [re ferred to Linck, 1949, pl. 8, fig. 1].
nomen nudum 1994, Lockeia seriali n. ichnosp.– Seilacher et Seilacher, 10.
2009, aligned Lockeia amygdaloides (Seilacher, 1953) — Pieńkowski and Niedźwiedzki, 119, fig. 4: 2.
D e r i v a t i o n o f n a m e. — From the over all con i - cal shape of mounds in the chain.
M a t e r i a l a n d h o l o t y p e. — 3 slabs in the Pol - ish Geo log i cal In sti tute-Na tional Re search In sti tute (MUZ PGI 80.VI.139, 80.VI.140, 80.VI.141). The holotype is in the slab MUZ PIG 80.VI.139 (cut into four pieces A, B, C, D — pieces A and B is the holotype). The same slab was il lus trated by Pieńkowski and Niedźwiedzki (2009, fig. 4: 2) and named as
“aligned Lockeia amygdaloides bur rows”. The paratypes are the slabs MUZ PGI 80.VI.140, PGI 80.VI.141. Seven small slabs in the In sti tute of Geo log i cal Sci ences of the Jagiellonian Uni ver sity (INGUJ 211P1-7); the paratype is INGUJ 211P5.
D i a g n o s i s. — Straight to slightly wind ing chain of hypichnial, mostly con i cal mounds, which can partly over lap.
D e s c r i p t i o n. — Rows of hypichnial mounds on a sand stone bed. The mounds are con i cal or pouch-like, iso met - ric or elon gate, round to oval or slightly lobate oval in out line, 13–38 mm wide, 18–35 mm long, as much as 30 mm high. The sur face of the mounds is smooth, or only hav ing ir reg u lar, gently slop ing con cav i ties of con vex i ties. Their top is hemi - spher i cal or flat.
The rows con tain 3 to at most 16 mounds. Edges of the mounds in the row over lap (Figs. 4A, 5A, B, 6A and 7A, B) or less com monly are iso lated (Figs. 4C and 5C–E). Api ces of the mounds are lo cated 15–25 mm apart and as much as 63 mm be - tween the iso lated mounds. The lon gest rows ob served are at least 350 mm long, with 15 or 16 mounds (Fig. 6A). They are trun cated by the edge of slabs, and prob a bly are much lon ger.
In some larger slabs the rows run sub-par al lel or cross-cut at an acute an gle up to 50° fol low ing more or less the same di rec tion (Fig. 6A). In some slabs the rows are so crowded that they are dif fi cult to fol low (Fig. 6B); the sand stone sole looks like a field of mounds. In the crowded spec i mens, curved, semi cir cu - lar ridges, about 5 mm wide, run ir reg u larly be tween the mounds (Fig. 6B). It is not clear if they be long to Ptychoplasma or not.
Fig. 3. Sołtyków out crop re veal ing al lu vial plain-lac us trine mudstones and chan nel/cre vasse splay sand stones (ar rowed)
The main me an der ing chan nel is vis i ble on the left. In set: multi-stage sed i men ta tion of the cre vasse splay (type 1) with ero sional sur faces bound ing suc ces sive flood events (ar rowed); Ptychoplasma conica isp. nov. was found in the cre vasse
splay fa cies il lus trated on this pho to graph
Some of the mounds dis play sin gle cav i ties, which show steep, smooth walls, an oval out line with semi-rounded mar gin at one side, and pointed mar gin at the op po site side of lon ger axis of the oval (Fig. 6B). The de pres sions are 30 mm long, 15 mm wide, and as much as 10 mm deep, 23–27 mm long and 11–15 mm wide. In some bro ken mounds, an out line of a bi - valve shell can be vis i ble (Fig. 7A).
The trace-fos sil bear ing sand stone beds lo cally dis play meniscate ver ti cal struc tures, with menisci con vex down, about 25 mm wide, with out dis tinct mar gins (Fig. 4A). These are con - sid ered as es cape (fugichia) struc tures of the tracemaker. Com - monly, the trace fos sil bear ing layer is sep a rated from the higher layer by an amal gam ation sur face, which trun cates the bur rows (Fig. 4A). In hor i zon tal sec tions, the trace-fos sil bear -
402 Grzegorz Pieńkowski and Alfred Uchman
Fig. 4. Ptychoplasma conica isp. nov. in sand stone slabs
A — ver ti cal cross-sec tion. Note the basal layer with cross sec tion along a row of Ptychoplasma conica isp. n., which is sep a rated by an amal gam - ation sur face (ar rows) from the up per layer. The up per layer is cross cut by an es cape struc ture (fugichnion) of the tracemaking bi valve (fu), MUZ PIG 80.VI.139 (holotype); B — lower sur face of the cut slab shown in A; C — lower sur face of a sand stone bed with mounds of Ptychoplasma conica isp. n., MUZ PIG 80.VI.140; D — hor i zon tal sec tion of the slab shown in B. Note elon gated bioturbational struc tures and a de pres sion of a bi valve ex ter nal mould (b)
ing layer dis plays mostly elon gated bioturbational struc tures, with poorly ex pressed con cen tric struc tures (Fig. 4D). In ver ti - cal sec tion, the mounds dis play a con i cal core sur rounded by an en ve lope of slightly dif fer ent li thol ogy (Fig. 5D). The in ter nal struc tures are re lated to the se quen tial move ments of the tracemaker.
R e m a r k s. — Ptychoplasma excelsa Fenton and Fenton, 1937 dis plays less dis tinct, slightly elon gated mounds. Tuberculichnus vagans Książkiewicz, 1977 and its ju nior syn onym Hostynichnium du plex Plička et Siráňova, 1989, which are in cluded in Ptychoplasma (Mikuláš, Rind - sberg and Uchman, sub mit ted) dis plays elon gate mounds pointed at both ends, ar ranged in a com monly strongly wind -
ing or loop ing row. As yet, no more ichnospecies of Ptycho - plasma are known.
Seilacher and Seilacher (1994) pro posed a new ichnospecies Lockeia serialis, which was re ferred to the ma te rial termed “Muschelspur” i.e. “bi valve trace” and il lus trated by Linck (1949) from the Up per Tri as sic Stuttgart For ma tion (“Schilfsandstein”) of the Keuper Group (megafacies) in Ger - many. It was di ag nosed by Seilacher and Seilacher (1994) as a
“...repichnial ver sion of Lockeia, ex pressed by se rial align ment of amygdaloid undertraces...”. Linck (1949) did not used the term “Muschelspur” but de scribed and il lus trated it (p.
666–669, pl. 8, figs. 1–2) as an “einzeilige Reihenhöcker- Spur”, i.e. “... a sin gle row of humps...”, which ac cords with the
Fig. 5. Dif fer ent ap pear ance of Ptychoplasma conica isp. nov. in sand stone slabs
A, B — Ptychoplasma conica isp. nov. in rows with over lap ping mounds, field pho to graphs; C — row with iso late mounds, field pho to graph;
D — ver ti cal sec tion of a mound, ING UJ 211 P1; E — side view of two sep a rated mounds, ING UJ 211P3a
di ag no sis by Seilacher and Seilacher (1994). Be cause no holotype was des ig nated, Lockeia serialis Seilacher et Seilacher, 1994 is a nomen nudum (Schlirf et al., 2000). Rietschel (1965), Vossmerbäumer (1970) and Pieńkowski (1991) il lus trated lo - co mo tion trails of bi valves from nearshore-coastal plain lower Hettangian de pos its from Helsingborg, Scania, South ern Swe - den. Also, es cape struc tures made by bi valves, sim i lar to those de scribed herein (al though smaller), were de scribed by these three au thors. The first two au thors named these rows of amygdaloid trails as Pelecypodichnus amygdaloides, the third au thor as signed those trails to Imbrichnus isp. In all cases they dif fer from Ptychoplasma conica isp. nov. by hav ing smaller, more reg u lar, non-con i cal, al mond- to lens-shaped mounds in the chain. The trails from Scania rep re sent Ptychoplasma isp., but they should be de fined as a sep a rate ichnogenus.
Pieńkowski and Niedźwiedzki (2009) de scribed aligned Lockeia amygdaloides from Sołtyków lo cal ity, which is iden ti - cal to those de scribed herein (one slab il lus trated by Pieńkowski and Niedźwiedzki is ac tu ally the holotype of Ptychoplasma conica isp. nov.). They also il lus trated sim i lar but smaller forms (their fig. 6).
DISCUSSION
The ichnogenus Lockeia James, 1879 is a rest ing trace (cubichnion), but Ptychoplasma conica isp. nov., even if its ba - sic mor pho log i cal el e ments are com posed of Lockeia-like struc tures, is a lo co mo tion trace fos sil that be longs to a dif fer - ent etho log i cal cat e gory, i.e. repichnion. This dis tinc tion re - quires a sep a rate ichnogeneric as sign ment, and the ichnogenus Ptychoplasma Fenton and Fenton, 1937 is the best choice for this repichnion.
The char ac ter is tic mound-like shape and body fos sils in Ptychoplasma conica isp. nov. in di cate bi valves as the tracemakers of this trace fos sil. Pres er va tion of the body fos sils
as moulds of shells does not al low for closer de ter mi na tions but ac cord ing to Niedźwiedzki (pers. comm., 2008) and Fürsich (pers. comm., 2008), they be long to the Unionidae. Mem bers of this fam ily are typ i cal fresh wa ter taxa, which are com mon in flu vial en vi ron ments.
Ptychoplasma conica isp. nov. oc curs in amal gam ated sand stone beds de pos ited in a river cre vasse. Tracemaking bi - valves moved more or less to ward the di rec tion of flow. Mod - ern river-dwell ing unionoids show pre ferred ori en ta tion with the sagittal plane of the shell par al lel to cur rent flow, with the long axis of the shell dip ping down stream (Thoms and Berg, 1985; Johnston and Hendy, 2005). Pieńkowski and Niedźwiedzki (2009) claimed that align ment of this trace fos sil was pre ferred and par al lel to the palaeocurrent di rec tion. The au thors also noted the ad ap ta tion of bi valve’s be hav iour to sed - i men ta tion. Bi valves pen e trated through out a sand layer a few centi metre thick, and com monly the low est part of their foot en - tered the un der ly ing mud. The sand was in tro duced in the re - sult ing de pres sion in the mud. The flat top of some mounds can be the re sult of fill ing of the low est part of the de pres sion by mud. Af ter weath er ing, the muddy part was eroded from the sandy part. The nearly iso met ric shape of the hypichnial mounds in di cates that lat eral move ment of the bi valve was made in the shal lower layer of sand. The mounds are a re cord of rest ing with a down ward and up ward move ment, lack ing any sig nif i cant lat eral com po nent.
The mor phol ogy of Ptychoplasma conica isp. nov. re flects re pet i tive, rhyth mic un du la tory move ment of the tracemaking bi valve. Such a move ment can be ex plained in dif fer ent ways.
It can re flect di ur nal rhythm, where the bi valve moves up and feeds, mov ing lat er ally dur ing the day when wa ters are warmer and dig ging down dur ing night for rest ing, or mov ing lat er ally to feed dur ing the night and dig ging down dur ing days when pred a tory dan ger is high. Al ter na tively, the rhythm can be re - lated to rhyth mic changes of flow in the cre vasse chan nel re - lated to pre cip i ta tion.
404 Grzegorz Pieńkowski and Alfred Uchman
Fig. 6. Other ap pear ances of Ptychoplasma conica isp. nov. on the lower sur face of sand stone slabs, field pho to graphs A — two gen er a tions of subparallel rows show ing par tial cross ing; B — crowded Ptychoplasma conica isp. nov. as so ci ated with curved ridges
We have not ex cluded the pos si bil ity that the mass oc cur - rence of Ptychoplasma conica isp. nov. in the base of the cre - vasse sand stone re flects in va sion by the bi valve in the flu vial plain dur ing the hu mid sea son. In such a sit u a tion, the river chan nel can play the role of refugium dur ing the dry sea son. Bi - valves can mi grate on the flu vial plain when it is flooded dur ing the rainy sea son.
Channelised cre vasse splays show a mul ti stage in fill ing with re ac ti va tion sur faces (Fig. 3) re flect ing mul ti ple floods.
Cer tainly, the feed ing bi valves were ex posed to heavy stress caused by ero sion and/or anastrophic depositional events. Such
stress forced the tracemakers to move ver ti cally, ei ther down - wards (some deep pro tru sive struc tures — Pieńkowski and Niedźwiedzki, 2009; Fig. 7C), or op po site, up wards, which was caused by rapid de po si tion as so ci ated with wan ing flood event (retrusive Scalichnus isp. de scribed by Pieńkowski and Niedźwiedzki, 2009 and meniscate es cape struc tures vis i ble in Fig. 4A). These ver ti cal, meniscate fugichnia are “com mu ni ca - tion chan nels” join ing the pre vi ous (deeper) with newer (shal - lower) tiers (Fig. 4A). Ob ser va tions of liv ing unionoids show that in un da tion by sed i ment prompts an up ward es cape re - sponse pro duced by down ward thrust of the foot (Thoms and Berg, 1985).
In ter est ingly, ex ter nal moulds of body fos sils of bi valves are lo cally found at the “blind” ends of pro tru sive ver ti cal shafts (Fig. 7C) or in side the bed (Fig. 4D). Likely, the “un - lucky” bi valves es cap ing pri mary ero sion faced even worse odds, when their hab i tat was cov ered by a thick layer of sandy sed i ment, rap idly de pos ited dur ing the flood-wan ing stage.
They could sim ply stay for ever in their ref uge (“taphonomic burial”), be ing un able to over come the over ly ing sed i ment bur - den. Likely, these bi valves would not even at tempt to es cape (there are no signs of up ward move ment).
Works of Rietschel (1965), Vossmerbäumer (1970) and Pieńkowski (1991) show that the be hav iour of con ti nen tal bi - valves — tracemakers of Ptychoplasma conica isp. nov. — did not dif fer sig nif i cantly from the brack ish-ma rine trace - makers of the trails from Scania. In the lat ter case, the nearshore cur rents and post-storm sed i men ta tion were re - spon si ble for align ment of the trails and es cape struc tures, re - spec tively (for post- storm es cape struc tures made by bi valves see also Pieńkowski, 1985).
As yet, Ptychoplasma conica isp. nov. is lim ited to the Late Tri as sic–Hettangian in terms of stra tig ra phy, and geo graph i - cally to Cen tral Eu rope. How ever, fur ther data are needed to mod ify or ver ify this view.
CONCLUSIONS
1. Ptychoplasma conica isp. nov. is a new lo co mo tive (repichnion) trace fos sil re lated to freshwa ter bi valves be long - ing prob a bly to Unionidae.
2. Ptychoplasma conica isp. nov. oc curs in cre vasse sed i - ments; the tracemaking bi valves moved more or less ac cord ing to the flow di rec tion.
3. Mor phol ogy of this trace fos sil re flects rhyth mic move - ment of the tracemaker, where lat eral move ment took place in the shal low part of the sand stone layer and was in ter rupted by rest ing ep i sodes in the deeper sed i ment layer along the mud-sand in ter face.
4. The “nor mal” (back ground) life con di tions were of ten in ter rupted by “cat a strophic” flood events, ex ert ing stress on the bi valves and forc ing them to move ver ti cally — some times down wards (es cape from ero sion), or more of ten up ward (es - cape from an anastrophic bur row). Re sult ing ver ti cal meniscate struc tures com monly link with the hor i zon tal tiers.
5. Ptychoplasma conica isp. nov. ranges from Later Tri as - sic to Hettangian.
Fig. 7. Ev i dence of the tracemaking bi valves of Ptychoplasma conica isp. nov.
A — bro ken mounds with out lines of dis solved shells (ar rows); B — ex ter - nal mould of shell (ar rows) at the end of a row; C — ex ter nal mould of a shell pre served at the end of a pro tru sive bur row, ex tracted from the trace fos sil bear ing bed; the shell prob a bly be longs to the Unionidae, MUZ PIG 80.VI.142
Ac knowl edge ments. A. Uchman was sup ported by the Jagiellonian Uni ver sity (BW 812 funds). G. Niedźwiedzki (Uni ver sity of War saw, Po land) was help ful dur ing field work and along with F. T. Fürsich (Erlangen Uni ver sity, Ger - many) pro vided his opin ion on body fos sils of the tracemaking bi valves. We thank R. Bromley (Geo log i cal Mu - seum, Co pen ha gen, Den mark), L. Buatois (Uni ver sity of Sas -
katch e wan, Can ada) and A. Mar tin (Emory Uni ver sity, USA) for use ful sug ges tions. This is a con tri bu tion to IGCP pro ject 506 “Ma rine and Non-ma rine Ju ras sic: Global Cor re la tion and Ma jor Geo log i cal Events”.
REFERENCES
ASLAN A. and AUTIN W. J. (1999) — Evo lu tion of the Ho lo cene Mis sis - sippi River floodplain, Ferriday, Lou i si ana: in sights on the or i gin of fine-grained floodplains. J. Sed i ment. Res., 69: 800–815.
EMERY D. and MYERS K. J., eds. (1996) — Se quence stra tig ra phy.
Blackwell Sc., Ox ford.
FARRELL K. M. (2001) — Geo mor phol ogy, fa cies ar chi tec ture, and high-res o lu tion, non-ma rine se quence stra tig ra phy in avul sion de pos - its, Cum ber land Marshes, Sas katch e wan. Sed i ment. Geol., 139:
93–150.
FENTON C. L. and FENTON M. A. (1937) — Bur rows and trails from Penn syl va nian rocks of Texas. Am. Mid land Natur., 18 (6):
1079–1084.
GALLOWAY W. E. and HOBDAY D. K. (1996) — Terrigenous clastic depositional sys tems. Springer-Verlag, Berlin.
GIERLIŃSKI G., NIEDZWIEDZKI G. and PIEŃKOWSKI G. (2001) — Gi gan tic foot print of a theropod di no saur in the Early Ju ras sic of Po - land. Acta Palaeont. Pol., 46 (3): 441–446.
GIERLIŃSKI G. and PIEŃKOWSKI G. (1999) — Di no saur track as sem - blages from Hettangian of Po land. Geol. Quart., 43 (3): 329–346.
GIERLIŃSKI G., PIEŃKOWSKI G. and NIEDZWIEDZKI G. (2004) — Tetrapod track as sem blage in the Hettangian of Sołtyków, Po land, and its Paleoenvironmental Back ground. Ichnos, 11 (3–4), Wil liam A. S.
Sarjeant (1935–2002) A Cel e bra tion of His Life and Ichnological Con tri bu tion. Spec. Is sue: Part 3, 195–213.
HÄNTZSCHEL W. (1975) — Trace fos sils and problematica. In: Trea tise on In ver te brate Pa le on tol ogy, Part W, Mis cel la nea, Sup ple ment I (ed.
C. Teichert). Geol. Soc. Am. Univ. Kan sas, Boul der, Law rence.
JAMES U. P. (1879) — De scrip tions of new spe cies of fos sils and re marks on some oth ers from the Lower and Up per Si lu rian rocks of Ohio. The Pa le on tol o gist, 3: 17–24.
JOHNSTON P. A. and HENDY J. W. (2005) — Paleoecology of mol lusks from the Up per Cre ta ceous Belly River Group. In: Di no saur Pro vin - cial Park: a Spec tac u lar An cient Eco sys tem Re vealed (eds. P. J. Cur rie and E. B. Koppelhus): 139–166. In di ana Univ. Press.
KSIĄŻKIEWICZ M. (1977) — Trace fos sils in the flysch of the Pol ish Carpathians. Palaeont. Pol., 36: 1–208.
LINCK O. (1949) — Lebens-Spuren aus dem Schilfsandstein (Mittl. Keuper km 2) NW-Württembergs und ihre Bedeutung für die Bildungsgeschichte der Stufe. Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg, 97–101 (for 1948): 1–100.
MÁNGANO M. G., BUATOIS L. A., WEST R. R. and MAPLES C. G.
(1998) — Con trast ing be hav ioural and feed ing strat e gies re corded by tidal-flat bi valve trace fos sils from the Up per Car bon if er ous of east ern Kan sas. Palaios, 13: 335–351.
M`COY F. (1850) — On some gen era and spe cies of Si lu rian Radiata in the col lec tion of the Uni ver sity of Cam bridge. Ann. Magaz. Natur. His tory, Ser. 2, 6: 270–290.
MIALL A. D. (1977) — Flu vial sedimentology. Ca na dian Soc. Petrol.
Geol. Notes, Oc to ber, Cal gary.
NANSON G. C. and CROKE J. C. (1992) — A ge netic clas si fi ca tion of floodplains. Geo mor phol ogy, 4: 459–486.
PIEŃKOWSKI G. (1985) — Early Li assic trace fos sils as sem blages from the Holy Cross Moun tains, Po land: their dis tri bu tion in con ti nen tal
and mar ginal ma rine en vi ron ments. In: Biogenic Struc tures: their Use in In ter pret ing Depositional En vi ron ments (ed. H. A. Curran). Soc.
Econom. Paleont. Miner., Spec. Publ., 35: 37–51.
PIEŃKOWSKI G. (1991) — Li assic sed i men ta tion in Scania, south ern Swe den: Hettangian–Sinemurian of the Helsingborg area. Fa cies, 24:
39–86.
PIEŃKOWSKI G. (1998) — Di no saur nest ing ground from the Early Ju - ras sic flu vial de pos its, Holy Cross Moun tains (Po land). Geol. Quart., 42 (4): 461–476.
PIEŃKOWSKI G. (2004) — The epicontinental Lower Ju ras sic of Po land.
Pol. Geol. Inst. Spec. Pap., 12.
PIEŃKOWSKI G. and GIERLIŃSKI G. (1987) — New finds of di no saur foot prints in Li assic of the Holy Cross Mts. and its palaeo - environmental back ground (in Pol ish with Eng lish sum mary). Prz.
Geol., 35 (4): 199–205.
PIEŃKOWSKI G. and NIEDZWIEDZKI G. (2009) — In ver te brate trace fos sil as sem blages from the Lower Hettangian of Soltyków, Holy Cross Moun tains, Po land. Pro ceed. 7th In ter na tional Con gress on the Ju ras sic Sys tem, Sep tem ber 6–18, 2006, Kraków, Po land. Vol.
Jurassica, 6: 89–104.
PLIČKA M. and SIRÁŇOVA Z. (1989) — Hostynichnium du plex ichnogen.
n. sp. n. — a new trace fos sil from the Carpathian flysch of Czecho slo va - kia. Západne Karpaty, Sér. Paleont., 13: 109–112.
RIETSCHEL S. (1965) — Muschelspuren aus dem Lias von Schonen.
Natur und Mu seum, 95: 447–454.
RINDSBERG A. K. (1994) — Ichnology of the Up per Mis sis sip pian Hartselle Sand stone of Al a bama, with notes on other Car bon if er ous For ma tions. Geol. Surv. Al a bama, Bull., 158: 1–107.
SCHLIRF M., UCHMAN A. and KÜMMEL M. (2001) — Up per Tri as sic (Keuper) non-ma rine trace fos sils from the Haßberge area (Franconia, south-east ern Ger many). Paläontologische Zeitschrift, 75: 71–96.
SEILACHER A. and SEILACHER E. (1994) — Bivalvian trace fos sils: a les son from actuopaleontology. Cou rier Forschung Senckenberg, 169:
5–15.
THOMS R. E. and BERG T. M. (1985) — In ter pre ta tion of bi valve trace fos sils in flu vial beds of the basal Cats kill For ma tion (late De vo nian), east ern U.S.A. In: Biogenic Struc tures: their Use in In ter pret ing Depositional En vi ron ments (ed. H. A. Curran). Soc. Econom. Paleont.
Miner., Spec. Publ., 35: 13–20.
VOSSMERBÄUMER H. (1970) — Untersuchungen zur Bildungsgeschichte des Unteren Lias in Schonen (Schweden). Geol.
Palaeont., 4: 167–193.
WCISŁO-LURANIEC E. (1991) — Flora from Odrowąż in Po land — a typ i cal Lower Li assic Eu ro pean flora. In: Palaeovegetational De vel - op ment in Eu rope and Re gions Rel e vant to its Palaeofloristic Evo lu - tion (ed. J. Kovar-Eder): 307–311. Pro ceed. Pan-Eu ro pean Palaeobot.
Con fer ence, Vi enna, 19–23 Sep tem ber, 1991.
WEGIEREK P. and ZHERIKHIN V. (1997) — An Early Ju ras sic in sect fauna in the Holy Cross Moun tains. Acta Palaeont. Pol., 42 (4):
539–543.
ZIAJA J. (2006) — Lower Ju ras sic spores and pol len grains from Odrowąż, Me so zoic mar gin of the Holy Cross Moun tains, Po land.
Acta Palaeobot., 46: 3–83
406 Grzegorz Pieńkowski and Alfred Uchman
