Perm ian trepostome bryo zoans from the Zechstein Main Do lo mite (Ca2) of West ern Po land and NE Ger many
Urszula HARA, Andrej ERNST and Zbigniew MIKO£AJEWSKI
Hara U., Ernst A. and Miko³ajewski Z. (2009) — Perm ian trepostome bryo zoans from the Zechstein Main Do lo mite (Ca2) of West ern Po land and NE Ger many. Geol. Quart., 53 (2): 249–254. Warszawa.
The trepostome bryo zoan Dyscritella microstoma Ernst, 2001 is re ported for the first time from the Zechstein Main Do lo mite (Ca2) of Po land and Ger many. This spe cies has been pre vi ously rec og nized in the older fossiliferous Zechstein Lime stone (Ca1) of the North Sudetic Ba sin (Po land) and in the north ern part of Ger many. The Pol ish spec i mens de rive from a few bore holes lo cated in the Pomerania re gion and in the Wolsztyn High, both in the west ern part of Po land. The Ger man ma te rial co mes from a bore hole on Rügen Is land in North east ern Ger many. The pres ent pa per deals with the tax o nomic de scrip tion of D. microstoma and its dis tri bu tion in the Main Do lo - mite de pos its.
Urszula Hara, 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:
urszula.hara@pgi.gov.pl; Andrej Ernst, Institut fur Geowissenschaften der Chris tian-Albrechts-Universität zu Kiel, Ludewig-Meyn-Str.
10, D-24118, Kiel, Ger many, e-mail: ae@gpi.uni-kiel.de; Zbigniew Miko³ajewski, Polskie Górnictwo Naftowe i Gazownictwo SA (PGNiG), Oddzia³ w Zielonej Górze, pl. Staszica 9, PL-64-920 Pi³a, Po land, e-mail: zbigniew.mikolajewski@pgnig.pl (re ceived: July 09, 2008; ac cepted: April 1, 2009).
Key words: West ern Po land, NE Ger many, Bryozoa, Zechstein, Main Do lo mite (Ca2), tax on omy.
INTRODUCTION
Bryo zoans are an im por tant com po nent of the Zechstein Lime stone (Ca1) fos sil as sem blages and they have been re - ported mainly from the Fore-Sudetic Monocline and the Lower Silesia area since the sec ond half of the 19th cen tury by many Ger man and Pol ish re search ers (Hara, 2001).
Their oc cur rence in the Wolsztyn High (West Po land) is con nected with in situ bi o log i cally-cre ated car bon ate build ups, which show sat is fac tory res er voir prop er ties (Dyjaczyñski et al., 2001). Al gal-bryo zoan car bon ate ac cu mu la tions are com - mon in the Ca1 ho ri zon and they lo cally at tain con sid er able thicknesses, reach ing 100 metres, as a con se quence of a com - plex in ter play of sea level fluc tu a tion and tec tonic sub si dence, be ing po ten tial traps for gas ac cu mu la tion (Dyjaczyñski et al., 2001; Kiersnowski et al., 2007).
By con trast, bryo zoans are very rare in the sec ond car bon - ate level of the Zechstein, the Main Do lo mite (Ca2). An un - named bryo zoan col ony has been re corded and il lus trated from the Main Do lo mite micritic strata in the shal low shelf plain fa - cies of the Ujazd 1 bore hole of the Fore-Sudetic Monocline
(Peryt, 1978). A few other re cords of this fauna are known from the Pol ish Low land area (Wag ner, 1994) and the Peribaltic Syneclise (Karczewski, 1986). Un con firmed re cords of bryo - zoans were also men tioned by Kerkmann (1969) from the youn ger parts (Ca2 to Ca3) of Zechstein in Thuringia.
Dyscritella microstoma as de scribed here has been rec og - nized in a few bore holes of Pomerania (NW Po land) and in the Pogorzela High (Fore-Sudetic Monocline). The pres ence of the bryo zoan fauna in thin sec tions from the Pomerania area is lim - ited to the plat form (in ner shelf en vi ron ment) fa cies such as in the microplatform de pos its of Unis³aw (Unis³aw IG 2 bore - hole) and of the Pom er a nian Plat form (S³awoborze 2 bore hole).
Fur ther more, it has also been rec og nized in the basinal fa cies (outer shelf palaeoenvironment set ting) of the Czaplinek IG 2 bore hole, where the ma te rial was trans ported by wave ac tion or by tur bid ity cur rents (Fig. 1).
D. microstoma has also been doc u mented from the Main Do lo mite in the north east ern part of Ger many (Rügen Is land).
The age of these de pos its is con firmed by a bi valve and ostracod fauna (D. Weyer, pers. comm.).
The cur rently ac cepted stra tig ra phy of the Zechstein de pos its in Pogorzela 1 and the Pogorzela 2 bore holes based on 3D seis - mic data in ter pre ta tion in di cates that, in the most el e vated part of
SHORT COMMUNICATION
the Pogorzela High, the Main Do lo mite de pos its lie di rectly on the Car bon if er ous base ment (Kwolek and Miko³ajewski, 2007).
The pri mary pur pose of this study is to de scribe Dyscritella microstoma tax o nom i cally from the Zechstein Main Do lo mite and to dis cuss its palaeo ec ol ogy and dis tri bu tion.
SYSTEMATIC PALAEONTOLOGY
Phy lum Bryozoa Ehrenberg, 1831 Class Stenolaemata Borg, 1926 Or der Trepostomida Ulrich, 1882
Fam ily Dyscritellidae Dunaeva and Morozova, 1967 Ge nus Dyscritella Girty, 1911
Type-spe cies Dyscritella robusta Girty, 1911 Lower Car bon if er ous, North Amer ica
D i a g n o s i s. — Dendroid, mas sive and en crust ing col - o nies with abun dant acanthostyles and exilazooecia.
Autozooecia par al lel to lon gi tu di nal di rec tion of the col ony in endozone; grad u ally bend ing out wards in exozone. Di a - phragms in autozooecia lack ing or very rare; lack ing in exilazooecia. Exilazooecia cir cu lar to an gu lar in cross-sec tion and sep a rated from the autozooecia and from each other by thick walls. Two sizes of acanthostyles may be pres ent: one set large with few per autozooecia, the other set is small with sev - eral around each autozooecium. Zooecial walls thin in endozone, rap idly thick en ing in the exozone.
C o m p a r i s o n. — Dyscritella Girty, 1911 dif fers from the ge nus Dyscritellina Morozova (in Dunaeva and Morozova, 1967) by rare or ab sent di a phragms and less dif fer en ti ated acanthostyles.
O c c u r r e n c e. — De vo nian to Tri as sic; world wide.
Dyscritella microstoma Ernst, 2001 (Figs. 2–3, Ta bles 1 and 2)
2001 Dyscritella microstoma Ernst: 139, pl. 1 figs. 3–5.
M a t e r i a l. — Stud ied and mea sured spec i mens from Ger - many in clude 3 com plete col o nies as well as 11 thin sec tioned col - o nies. Un mea sured ma te rial in cludes about 50 un pre pared col o - nies. Up per Perm ian (Main Do lo mite, Zechstein); Rügen Is land, NE Ger many, Wiek 101 bore hole, depth 989.85–993.35 m and 996.55–1000.0 m (de pos ited at Bundesanstalt für Geowissenschaften und Rohstoffe [BGR], Berlin).
Stud ied and mea sured ma te rial from Po land in cludes two thin sec tions from Pogorzela 2 bore hole, (depth 1743 m), SW Po land, and two thin sec tions from Unis³aw IG 2 bore hole, (depth 3640.5–3635.5 m), NW Po land. Ad di tional ma te ri als stud ied de rived from one thin sec tion from the Czaplinek IG 1 bore hole (depth 3204,9 m), Pomerania area, NW Po land, and one thin sec tion from the S³awoborze 2 bore hole (depth 3248–3265 m), Pomerania re gion, NW Po land. All the stud ied ma te rial is from the Main Do lo mite; Pogorzela 2 and S³awoborze 2 bore holes are de pos ited at PGNiG S.A., War - saw, Zielona Góra branch; Unis³aw IG 2 and Czaplinek IG 1 bore holes are de pos ited at the PGNiG S.A., War saw, Po land.
One thin sec tion used for this study de rives from the Zechstein Lime stone (Ca1) of the North Sudetic Ba sin, SW Po land, shown in Fig ure 2A.
D e s c r i p t i o n. — En crust ing and dis coid fungi-shaped col o nies. En crust ing col o nies up to 4 mm thick, dis coid col o nies 1.6–2.8 mm in di am e ter and 1.1–1.2 mm thick in cen tral part. Autozooecial ap er tures oval to an gu lar (Figs. 2B and 3G, H), 7–9 spaced in 2 mm of col ony sur face. Di a phragms in autozooecia rare to ab sent. Walls in endozone 0.01 mm thick, in exozone 0.02–0.04 mm thick and obliquely lam i nated.
Exilazooecia po lyg o nal in cross-sec tion, com mon to rare, re - stricted to the late exozone. Acanthostyles abun dant, vary ing sig nif i cantly in size, orig i nat ing in the early endozone, with dis - tinct cores, 2–6 sur round ing each ap er ture, of ten in flect ing deeply into the autozooecium (Figs. 2B and 3G, H).
Fig. 1. Frag ment of the palaeo geo graphi cal map of the Zechstein Main Do lo mite of (Ca2) in the west ern part of Po land
(af ter Wag ner 1998, mod i fied)
Fig. 2. Dyscritella microstoma from the Zechstein Lime stone (Ca1) of Po land
A — North Sudetic Ba sin, tan gen tial sec tion show ing part of the col ony, scale bar = 1 mm; B–D — Unis³aw Plat form, SE Pomerania, Unis³aw IG 2 bore - hole, 3635.5 m depth: B — tan gen tial sec tion through part of the col ony, scale bar = 0.5 mm, C — trans verse sec tion through a frag ment of col ony, scale bar = 1 mm, D — trans verse sec tion through part of the col ony, scale bar = 1 mm; E, F — Fore-Sudetic Monocline, Pogorzela 2 bore hole, 1743 m dept: E — frag ment of col ony in trans verse sec tion, scale bar = 1 mm, F — lon gi tu di nal sec tion through frag ment of a col ony, scale bar = 1 mm
Fig. 3. Dyscritella microstoma from the Zechstein Main Do lo mite (Ca2), Rügen Is land, north east ern Ger many, Wiek 101 bore hole, depth 989.85–993.35 m (A, B, D–H) and 996.55–1000.0 m (C)
A — dis coid col ony, SEM, scale bar = 0.5 mm; B — en crust ing col ony, free of sub strate, SEM, scale bar = 1 mm; C — dis coid col ony, SEM, scale bar = 1 mm; D — lon gi tu di nal sec tion of a dis coid col ony, scale bar = 0.5 mm; E — lon gi tu di nal sec tion of a dis coid col ony, scale bar = 1 mm; F — deep tan gen - tial sec tion of a col ony, scale bar = 1 mm; G — tan gen tial sec tion of a col ony, scale bar = 0.2 mm; H — tan gen tial sec tion of the col ony, scale bar = 0.2 mm
C o m p a r i s o n. — Dyscritella microstoma Ernst, 2001 dif fers from D. tubulosa Morozova, 1970 (Up per Perm ian, Zechstein of Lith u a nia) by hav ing smaller autozooecial ap er - tures, thin ner walls as well as smaller and more abun dant acanthostyles.
O c c u r r e n c e. — Dyscritella microstoma Ernst, 2001 was orig i nally de scribed from the Zechstein Lime stone (Ca1) of Ger many. The ma te rial in ves ti gated co mes from the Main Do lo mite (Ca2) Zechstein of Rügen Is land, NE Ger many, and from Pogorzela 2 bore hole, Fore-Sudetic Monocline, West Po - land, and the Unis³aw IG 2 bore hole, Pomerania, NW Po land, as well as from the Zechstein Lime stone (Ca1) of the North Sudetic Ba sin, SW Po land.
DISCUSSION AND CONCLUSIONS
Al though the Zechstein bryo zoans show low mor pho log i - cal and tax o nom i cal di ver sity, mostly caused by a sig nif i cant fluc tu a tion in the tem per a ture and sa lin ity re gime of the Perm - ian ba sin (Ross, 1995), they play an im por tant role as
frame-build ing or gan isms in the Zechstein Lime stones (Ca1).
By con trast, the bryo zoan fauna in the Zechstein Main Do lo - mite (Ca2) is very rare and usu ally fragmentarily pre served (Fig. 2B–F), and its sig nif i cance is much smaller than in the Zechstein Lime stone (Ca1).
The oc cur rence of the bryo zoan fauna in the basal fa cies of a unique car bon ate ho ri zon, di rectly over ly ing the Car bon if er - ous rocks, was a strong ar gu ment to sug gest that it was the Zechstein Lime stone (Ca1). The re cent strati graphi cal in ter pre - ta tion of the Zechstein de pos its of the Pogorzela High, in the light of 3D seis mic data, sug gests that PZ1 (cyclothem Werra) strata are ab sent in the close vi cin ity of the Pogorzela High and the Car bon if er ous base ment is di rectly over lain by rocks of the Main Do lo mite (Ca2). Prob a bly, ini tial stages of the Zechstein trans gres sion did not reach the most el e vated part of the High (Kwolek and Miko³ajewski, 2007). The rock se quence shows that the most el e vated part of the Pogorzela High was an is land dur ing the Zechstein trans gres sion (Kwolek and Miko³ajewski, 2007; Kiersnowski et al., 2007). A sim i lar se quence was found in the Koszalin–Chojnice Zone where the Zechstein trans gres - sion did not flood all base ment highs. These highs formed is - lands sur rounded by al gal and al gal-bryo zoan bar ri ers, hav ing sev eral tens of metres in thick ness and sep a rat ing the la - goonal-lit to ral part of the ba sin from the open sea (Wag ner, 1987; Kwolek and Miko³ajewski, 2007).
The new ma te rial of D. microstoma de scribed here re veals two dif fer ent col ony forms: en crust ing and fungi-shaped (Figs. 2–3). Among the Pol ish ma te rial from the Main Do lo - mite (Ca2) bryo zoans en crust shells (Fig. 2C, E) as well as soft, de cayed sub strates such as al gae (Fig. 2D). In this en vi ron ment, the col o nies were ap par ently pro vided with enough hard sub - strate such as skel e tal frag ments, and they were not af fected by a high sed i men ta tion rate. More over, the bryo zoan col o nies in their small sizes and very low di ver sity may sug gest that they lived in a shal low-wa ter, low-en ergy, tidal, sub-tidal or la - goonal wa ter en vi ron ment.
By con trast, the ma te rial from the Wiek 101 bore hole (Rügen Is land) rep re sents pre dom i nantly fungi-shaped col o - nies (Fig. 3A, C, D–E), pre sum ably re sult ing from a scar city of hard sub strates and pos si bly a higher rate of sed i men ta tion.
Col o nies of D. microstoma are sim i lar to horn-shaped col o - nies of the trepostome bryo zoan Dianulites petropolitanus from the Or do vi cian of the Bal tic re gion (Modzalevskaya, 1955; Tay - lor and Wil son, 1999). The basal (lat eral) part of such col o nies is built by an epitheca. An other vari a tion of such a col ony form com prises tongue-shaped pro lon ga tions (Fig. 3B, F). Tay lor and Wil son (1999) sug gested that such col o nies lived as in verted cones semi-infaunally in soft sed i ments with their liv ing tis sues con fined to the ex posed up per sur face. Fur ther more, such col o - nies would in di cate a high rate of sed i men ta tion (see also Spjeldnaes, 1996). Sim i larly, the dis coid col o nies of Dyscritella microstoma may in di cate a shal low, quiet en vi ron ment with soft sub strates and mod er ately high sed i men ta tion rates.
Com par a tive ma te rial of D. microstoma ( Fig. 2A) from the Zechstein Lime stone (Ca1), ex hib its only an en crust ing growth habit (Hara, 1998).
D. microstoma, un doubt edly, dem on strates the intraspecific plas tic ity of the co lo nial form, de pend ing on the type of sub strate and other pa ram e ters such as sed i men ta tion
N X SD CV MIN MAX
Ap er ture
width 20 0.19 0.036 19.34 0.12 0.24
Exilazooecia
width 12 0.07 0.018 24.89 0.04 0.11
Acanthostyle
di am e ter 20 0.026 0.004 15.02 0.021 0.03 Num ber of
acanthostyles per ap er ture
20 3.6 1.5 41.61 2.0 6.0
N — num ber of mea sure ments; X — mean; SD — stan dard de vi a tion; CV — co ef fi cient of vari a tion; MIN — min i mum value; MAX — max i mum value
T a b l e 1 De scrip tive sta tis tics of the spe cies Dyscritella microstoma Ernst,
2001 (ma te rial from the Unis³aw IG 2 bore hole, Po land)
N X SD CV MIN MAX
Ap er ture
width 20 0.18 0.036 14.33 0.14 0.23
Exilazooecia
width 20 0.06 0.02 35.08 0.02 0.10
Acanthostyle
di am e ter 20 0.03 0.01 24.56 0.02 0.04
Num ber of acanthostyles
per ap er ture
23 3.6 1.40 38.47 2.0 7.0
Ex pla na tions as in Ta ble 1
T a b l e 2 De scrip tive sta tis tics of the spe cies Dyscritella microstoma Ernst,
2001 (ma te rial from the Rügen Is land, Ger many)
rate. The dif fer ence in the col ony shape cer tainly re flects dif - fer ent en vi ron ments at these lo cal i ties.
The ac com pa ny ing fauna within the stud ied se quences of the Zechstein Main Do lo mite (Ca2) is mostly dom i nated by mytiloid molluscs such as Liebea squamosa (Sowerby), myophorids Schizodus obscurus (Sowerby) and Schizodus schlotheimi (Geinitz), which is fairly com mon. Microfossils, es pe cially uniserial foraminifers, are quite com mon, as well as microbialite frag ments, whereas ostracods are rare. The mol - lusc fauna is an im por tant in di ca tor of a warm, highly sa line and shal low-wa ter en vi ron ment (Karczewski, 1986).
To sum up, the oc cur rence of the rare bryo zoan fauna, com - bined with fac tors such as the mor phol ogy of the co lo nial form and the char ac ter of the ac com pa ny ing fauna clearly sug gest that the bryo zoans of the Zechstein Main Do lo mite (Ca2) were de pos ited in a shal low-wa ter, low-en ergy en vi ron ment, with a pro gres sive in crease of the sa lin ity.
Dyscritella microstoma in di cates the palaeogeographic links within the Ger man and Pol ish Zechstein Ba sin. A com pa - ra ble spe cies, D. tubulosa Morozova, 1970, is also re stricted to the Zechstein Ba sin. Both these spe cies, how ever, are re lated to D. incrustata Morozova, 1970, from the Kazanian Stage of the East Eu ro pean Platform
Ac knowl edge ments. One of us (UH) is greatly in debted to R. Wag ner (Pol ish Geo log i cal In sti tute, War saw) for giv ing ac - cess to ad di tional re search ma te ri als from the Pol ish Zechstein Ba sin. Warm thanks are ex tended to H. Kiersnowski (Pol ish Geo log i cal In sti tute, War saw) for his valu able sug ges tions for im prove ment of the manu script. T. M. Peryt (Pol ish Geo log i cal In sti tute, War saw) is es pe cially ac knowl edged for his thought - ful re view of the manu script. S. Brandt (Halle) and D. Weyer (Berlin) are thanked for help ful com ments to stra tig ra phy.
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