GEOLOGICA BALCANICA, 30, 3-4, Sofia, Febr. 2001, p. 29-42

Dispersed tubular structures and filaments from Upper Silurian -Middle Devonian marine deposits of North Bulgaria and Macedonia

Iskra Lakova

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia e-mail: lakova@geology.bas.bg 1Received 01.11.2000; accepted 03.11.2000)

H. JlaKoBa - JI.ucnepCHbLe mpy6'1ambLe cmpyKmypbl u HUmbl U3 8epxHeCU11JpU11CKUX - cpeiJHeiJeBOHCKUX MOp­CKUX omAo:>~eeHuu CeBepHou EoAi!apuu u MaKeOoHuu. B JTOH pa6oTe npe.ncTaBJieH&I coo6ruecTBa Tpy6tJaT&IX CfPYKTYP H HHT H3 qepHbiX aprHJIJ!HTOB noJ.nHeCHJiy­?RHCKOfO - Cpe.nHe.neBOHCKOfO B03pacTa B CKBa~HHaX \iHJHHCKOH nJIHTbJ. CtJHTaeTC$1, 'ITO 3TH Tpy6KH H HHTbi ~JJ$1lOTC$1 'JaCTb$1MH nepBbiX Bb!CUIHX pacTeHHH Ha cyUie. YcTaHOBJieHO rpHHa.nu.aTb BH.nOB, OTHOC$1lUHXC$1 K aHTe­TJ'PMe Trichomiformis Burgess & Edwards, TaK~e KaK H J Ba HOBbiX BH.na: Porcatitubulus reticu/atus u Ornatifilum macedonensis. B naJIHHOJIOrH'IeCKHX npenapaTax 3TH rpy6tJaT&Ie H HHHaT&Ie CTPYKTYPbi BCTpetJalOTC$1 coa­l-JeCTHO C aKpRTapxaMR, XHTHH030$1MR, CKOJieKO.nOH­Ta.\!R, cnopaMH H KYCKaMH KYTHKyJI, npH 'JeM XHTHH030H 4Cll0Jlb30BaHbl _nJl$1 onpe.neJieHH$1 B03pacTa. J13 TeMHO­'!aTbiX CJlaHU.eB nOJ.nHeCRJJYPRHCKOro-paHHe.neBOHCKOrO !()3pacTa B O.nHOM H3 MeCTOHaXO~.neHHH B BOCTO'JHOH ~CTH MaKe.noHHH Tax~e 6&IJIH o6Hapy~eH&I .nsa BH.na :-;>y6l{aT&Ie CTPYKTYPbi H HHTbi. OnHc&maeM&IH J.nec& na­.::;monorHtJeCKHH MaTepHaJI npe.ncTaBJI$1eT co6oii neps­;,;ce 6oraT&Ie coo6ruecTBa Tpy6tJaT&IX H HHT'JaT&IX cTpyK­:-:•p, ycTaHOBJieHH&Ie a pa3pe3ax a IOro-BocTO'IHOH Ea­-;::cne, KOTopa$1 B cpe.nHeM naneOJoe pacnonaranac& ;J.:OJlb ceaepHOH nepHQJepHH roH.nBaH&J. 3TH coo6mecT­ae 6JIR3KH K KOMnJieKcaM Tpy6tJaT&IX CTPYKTYP Toro ~e aaJpacTa R3 .npeBHRX KOHTHHeHTOB JlaapeHTH$1, Aaano­e::u R oaJITRKa, 'ITO nonaraeT KOCMonoJTHTH'IecKoe pac­~aHeHHe HaJeMHblX pacTeHHH, CB$13aHHbiX C 3THMH wn-roQJHTOQJOCHJT$1MH. Bnepa&Je rpy6tJaT&Ie crpyKTYPbi

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a:.n.~ TPRMepoQJRTOB&IX R JocTepoQJHJIOBbiX pacTeHHH R3 iJe;IXHero cHnypa EonrapHH noJBOJTHJOT npe.nnono~HTb, - 3TH cocy.nHCTble pacTeHH.II llO.IIBHJ!HCb Ha nepHQJepHH ~ROH roH.nBaHbl paH&Uie 'JeM B JlaapeHTHH H ABa­.lii:EHl'J-oaJITHKe.

Abstract. Assemblages of tubular structures and filaments from Upper Silurian (Pridoli) - Middle Devonian (Eife­lian) marine black shales of the subsurface of the Moesian Platform are reported. These tubes and filaments are be­lieved to derive from early land plants. Thirteen species of the Anteturma Trichomiformis Burgess and Edwards are described. Two new species are proposed: Porcatitubulus reticu/atus and Ornatifilum macedonensis. The tubes and filaments are associated in palynological preparations with acritarchs, chitinozoans, scolecodonts, spores and cuticle fragments, the chitinozoans being used for age determination. Two species of tubes and filaments are also documented from dark grey schists of Late Silurian -Early Devonian age from easternmost Macedonia. The material described herein comprises the first comprehen­sive report of dispersed tubes and filaments from Upper Silurian - Middle Devonian deposits of Northern Gond­wana. It is similar to contemporaneous tubular structures and filaments from Laurentia-Avalonia-Baltica suggest­ing that the vegetation producing this phytodebris was cosmopolitan. The newly documented occurrence of tubes and filaments in the Emsian - Eifelian deposits ex­tends their upper stratigraphical range. The finds of com­plex tubular structures resembling tracheids of trimero­phytes and zosterophylls from the uppermost Silurian of Bulgaria suggest that some groups of vascular plants pos­sibly emerged in Northern Gondwana earlier than in Lau­rentia and Avalonia-Baltica.

29

Lakova I. 2000. Dispersed tubular structures and filaments from Upper Silurian - Middle Devo­nian marine deposits of North Bulgaria and Macedonia.- Geologica Bale., 30, 3-4, 29-42 Key words: Upper Silurian- Middle Devonian, tubular structures, paleopalynology, Moesian Plat­form.

Introduction

In the last two decades, there has been a dra­matic increase in data on Late Ordovician -Early Devonian dispersed microfossils derived from early land plants, in the form of spores, cuticles, tubular and filamentous macerals. As for the tubular structures and filaments which are morphologically similar to the conducting tissue of modern terrestrial vascular vegetation, their study is essentially important for making both palaeoenvironmental and palaeobotanical suggestions. However, their biostratigraphical potential (these are longer-ranging forms) is obviously much lower than that of other wide­spread organic-walled microfossils, e.g. chiti­nozoans, acritarchs and spores.

Burgess, Edwards (1991) introduced an artifi­cial morphology-based classification of all known tubular and filamentous macerals en­globing them into the newly erected anteturma Trichomiformis. Before and after that, many authors mentioned, figured andfor described identical macerals deriving from continental or marine deposits and ranging from Silurian to Early Devonian in age. These are the records from Baltica and Laurentia - Ireland (Edwards et al., 1983), Scotland (Wellman, Richardson, 1993; Wellman, 1995), England (Eisenack, 1977, 1978), Norway (Smelror, 1987), Poland (Eisenack, 1972), Baltica Region ('Beyrichia Kalk', Eisenack, 1971), USA and Canada (McGregor and Narbonne, 1978; Pratt et al., 1978; Wood 1978; Strother, Traverse, 1979; Johnson, 1985; Gensel et al., 1991). The tubular and filamentous structures described by Bur­gess, Edwards (1991) derived from the Anglo­Welsh Basin of Great Britain.

Geological setting

The two main localities of tubular structures and filaments of the uppermost Silurian and Lower Devonian of Bulgaria are the subsurface sections of R-119 Kardam Well in Northeast­ern Bulgaria and R-1 Dalgodeltsi Well in Northwestern Bulgaria, both occurring in the southern part of the Moesian Platform (Fig. 1). The tubes and filaments were extracted from dark grey to black marine shales of the so-

30

called Kalarashi Formation (or, informally des­ignated as 'Calcareous-Terrigenous-Argilla­ceous Series'). The palynological preparations also contain other organic-walled microfossils of both marine (chitinozoans, acritarchs and scolecodonts) and terrestrial (trilete miospores and fragments of cuticles) origin. The co-oc­currence of chitinozoan faunas indicates a Pri­doli and Early Devonian age.

Recently, the present author reported her findings of several representatives of the an­teturma Trichomiformis Burgess and Edwards from Pridoli and Lower Devonian strata from the R-119 Kardam well (Lakova, 1995a). The chitinozoan species M argachitina elegans Taugourdeau and Jekhowsky and Fungochitina kosovensis Paris and Kriz proved the Pridoli Series between 3647 to 3704 m, whereas within the interval between 3393 to 3587 m the succes­sive first occurrences of the characteristic chit­inozoans Eisenackitina bohemica (Eisenack), Fungochitina lata (Taugourdeau & Jekhowsky) and Urochitina simplex Taugourdeau and Jekhowsky enabled the identification of Loch­kovian chitinozoan zones of global application (Lakova, 1999) (Fig. 2). The upper part of the Kalarashi Formation (3065-3393 m) yielded poor chitinozoan association. The presence of Bursachitina bursa (Taugourdeau and Jekhow­sky) indicates an Emsian age. The lowermost part of the Carbonate-Sulfate Series (CSS) in the R-119 Kardam Well (2800-3065 m) repre-

Fig. I. Location of the sections studied. - R-1 Da1godeltsi, Moesian Platform; 2 - R -119 Kardam, Moesian Platform; 3 - R -120 Ograzhden, Moesian Platform; 4 - Dolna Sasa section, eastern Macedonia

w -

Jl lu rhn - --Prldoll

w

8 w

§ w

8

Devonian Lower

Loebkovian I Pragian Calcm'eOUI-Terrigenous-Argillaceoua Series

§ w w 8

Fig. 2. Vertical distribution of tubular structures and filaments in R-119 Kardam well, NE Bulgaria

Middle

I Bm1ian Bifelian css

~-

i w

8

(1 I U[ill] J.fe r~ ~

SYSTEM

SERIES

STAGE

lORMAn ON

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ZONE

L CI'GUIU

L. laxu.r

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0 . gramdalum

0 . miiCedoMNti.J

EXPLANATION OF PLATE 1 All from the Kalarashi Formation, Moesian Platform; x 500 unless stated otherwise Figs 1, 3. Laevitubulus laxus Burgess and Edwards, 1991. l. R-1 Da1godeltsi, Prido\i, M. elegans chitinozoan Zone, depth 4999 m, sample 2164. 3. R-119 Kardam, Pridoli, M . elegans chitinozoan Zone, depth 3700 m, sample 3, slide 3/2. Figs 2, 4. Constrictitubulus cristatus Burgess and Edwards, 1991. R -119 Kardam, Pridoli, M. elegans chitinozoan Zone, depth 3698-3704 m, sample 31. 2- slide 31/l, 4- slide 31/2. Figs 5-6. Laevitubulus crassus Burgess and Edwards, 1991; R-119 Kardam, Pridoli, M . elegans chitinozoan Zone. 5. Depth 3698-3704 m, sample 31, slide 31/2, x 250. 6. Depth 3700 m, sample 3, slide 3/l, x 250. Fig. 7. Laevitubulus tenuis Burgess and Edwards, 1991. R-119 Kardam, Pridoli, depth 3647-3653 m, sample 32, slide 32/1. Figs 8-10. Laevitubulus plicatus Burgess and Edwards, 1991. 8. R -120 Ograzhden, Middle Devonian, depth 2412 m, sample 8, slide 8/2. 9, 10. R-119 Kardam, Pridoli, M. elegans chitinozoan Zone. 9. Depth 3698-3704 m, sample 31 , slide 31/2. 10. Depth 3700 m, sample 3, slide 3/l.

EXPLANATION OF PLATE 2 All from the Kalarashi Formation, Moesian Platform; x 500 Figs I, 2, 5, 8, II. Porcatitubulus annularus Burgess and Edwards, 1991. I, 2, 5. R-119 Kardam, Pridoli, M. elegans chitinozoan Zone, depth 3700 m, sample, 3, slide 3/2. 8. R -119 Kardam, Emsian, B. bursa chitinozoan Zone, depth 3160 m, sample 5, slide 5/3. II. R-1 Dalgodeltsi, Pridoli, M. elegans Zone, depth 5000 m, sample 217/2. Figs 3, 6, 12, 13. Porcatitubulus spiralis Burgess and Edwards, 1991. 3. R-119 Kardam, Lochkovian, U. simplex chitinozoan Zone, depth 3468-3474 m, sample 36; slide 36/2. 6. R-119 Kardam, Emsian, B. bursa chitinozoan Zone, depth 3160 m, sample 5, slide 5/3. 12. R-1 Dalgodeltsi, Pridoli, M .elegans chitinozoan Zone, depth 5000 m, sample 217/1. 13. R-119 Kardam, Pridoli, M . elegans Zone, depth 3700 m, sample 3, slide 3/2. Figs 4, I 0. Porcatitubulus microspiralis Wellman, 1995, R-119 Kardam. 4. Emsian, B. bursa chitinozoan Zone, depth 3160 m, sample 5, slide 5/2. I 0. Pridoli, M. elegans chitinozoan Zone, depth 3700 m, sample 3, slide 3/2. Figs 7, 9. Tubular structures similar to tracheids of Psilophyton charientos, R-119 Kardam. 7. Pridoli, M . elegans chitinozoan Zone, depth 3700 m, sample 3, slide 3/2. 9. Emsian,B. bursa chitinozoan Zone, depth 3160 m, sample 5, slide 5/3.

EXPLANATION OF PLATE 3 All from the Kalarashi Formation, Moesian Platform; x 500 unless stated otherwise Figs l -3, 7-9. Porcatitubulus reticulatus Lakova sp. nov. I. R-1 Dalgodeltsi, Lochkovian, F. lata chitinozoan Zone, depth 4879-4885 m, slide 2101, holotype. 2, 3. R-1 Dalgodeltsi, Lochkovian,£. bohemica chitinozoan Zone, paratypes; 2 - depth 4912 m, slide 2121 , 3- depth 4915 m, slide 18/2. 7. R-119 Kardam, Pridoli, M. elegans chitinozoan Zone, depth 3700 m, sample 3, slide 3/2, paratype. 8. R-1 Dalgodeltsi, Pridoli, M. elegans chitinozoan Zone, depth 4999 m, sample 2164, para type. 9. R -119 Kardam, Emsian,B. bursa chitinozoan Zone, depth 3160 m, sample 5, slide 5/6, x800, para type. Figs 4-5. Porcatitubulus microannulatus Wellman, 1995. R-1 Dalgodeltsi, Pridoli, M. elegans chitinozoan Zone, depth 4999 m, sample 2164. Fig. 6. Porcatitubulus strupus Wellman, 1995. R-119 Kardam, Pridoli, M. elegans chitinozoan Zone, depth 3700 m, sample 3, slide 3/2.

EXPLANATION OF PLATE 4 All figures x 500 Figs l-4, 7. Ornatifilum granularum Burgess and Edwards, 1991. 1-4. R-119 Kardam, Kalarashi Formation, Pridoli, M . elegans Zone, depth 3 700 m, sample 3, slide 3/2. 7. R -I Dalgodeltsi, Kalarashi Formation, Lochkovian, U. simplex - C. plusquelleci chitinozoan Zone, depth 4798 m, sample 17, slide 17/l. Figs 5, 6. Porcatitubulus spiralis Burgess and Edwards, 1991, R-119 Kardam, Kalarashi Formation. 5. Pridoli, M . elegans chitinozoan Zone, depth 3700 m, sample 3, slide 3/2. 6. Emsian, Bursachitina bursa chitinozoan Zone, depth 3160 m, sample 5. Figs 8- ll. Ornatifilum macedonensis Lakova, sp. nov. Sasa section, Rashcha Formation, ?Wenlock to Lower Devonian, thin-section 18 IZ. 9. Holotype. 8, l 0, II. Para types.

32

PLATE I

-'

~ ..

I. Lakova, Geologica Balcanica, 3-4/2000

..

~

4

9

10

PLATE II

1 2 3

10

• ·• · .. .... • .. '

. ·• •• ' -' o#" -. . ~ ,

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PLATE III

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PLATE IV

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9

R 1 D l d Its' - ago e 1 TUBES AND FILAMENTS

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tl.l ~ g ~ tl.l ~ ~ ....---

41100 4796.S 4800.0

..___ - 207, U. simplex-

""' 171Z C. plu.squelleci

f---

/ 2071,101.2 1---Cl (IS

Cl (IS >

4842.S 484S.S -~ 2081,209, U. simplex

""' 2091 M

Cl u 0

0 ~ ~ > 0

.d (i} u ~

u

~ 0 0 ~ -:a

4900

4879.0 488S.O

4910.0 4916.0

t=---2100,210, 2101,2102

1~ 21o3,2u F. lata

2104,212,

~ I~ 2121, 2123, E. bohemica

Cl ~ 4941.0 4947.0 '!!!!!!!!!!!!!!! -

18IZ, 213

1\ 2140,214, 2141,2142, M. elegans

1--(IS

0 2144, 21S M -o

=' M ~

Cfl ~ 5000 499S.O SOOl.O

-~ 216, 2161,

M. elegans 2163,2164, 217, 2181

G ~ -- core interval

reddish black ai1DtoDca abalca

Fig. 3. Vertical distribution of tubular structures and filaments in R-1 Dalgodeltsi well, NW Bulgaria

sents dark grey to black clayey limestones of Eifelian age proved by presence of the con-

onts Icriodus expansus Branson and Mehl arl Icriodus corniger Wittekind (Boncheva,

95) and by the chitinozoan Fungochitina pi­- a (Collinson and Scott) (unpublished data by -- e present author).

In the R-1 Dalgodeltsi Well (Fig. 3), the pres­- ce of the chitinozoans Margachitina elegans

d Fungochitina kosovensis indicates a Pridoli -~e between 4941 to 5001 m (Lakova, 1999). -pwards, between 4796.5 to 4916.0 m, the suc-

ive first occurrences of Eisenackitina bohe­:ica, Fungochitina lata and Urochitina simplex

nstrain a Lochkovian age. Tubular structures are also found in the Mid­"' Devonian of R-120 Ograzhden, Northeast

garia, at a depth of 2412 m, where a con-·ont association ofEifelian age was earlier re­.ded (Yanev, Boncheva, 1995). A palynological association of acritarchs and ere miospores found in dark grey schists of

-,. Rashcha Formation in the vicinity of Bul-

logica Balcanica, 3-4/2000

garian-Macedonian border (Osogovo Mts.) constrained a Wenlock to Early Devonian age (Lakova et al., 1995). Within the same forma­tion, at the locality of Dolna Sasa in the of Re­public of Macedonia (Fig.1 ), tubes of Laevitu­bulus laxus occur, as well as filaments of the newly described species Ornatifilum macedon­ensis.

Sampling, preparation and repository

Fifty nine core samples of black to dark grey shales have been collected and palynologica lly studied from the well sections R -119 Kardam and R-1 Dalgodeltsi in the Moesian Platform, as well as eleven samples of dark grey schists from outcoups of the Rashcha Formation in the Osogovo Mts (western Bulgaria and east­ernmost Macedonia). All samples of 50 g of rock were collected by the author and treated for palynological investigation using standard maceration techniques (HCl and HF acids) fol-

33

lowed by zinc bromide separation. Some sam­ple residues were oxidized in cold Schultz's so­lution. For light microscope observation, the residues were mounted with Elvacite mounting medium. Thin -sections have also been pre­pared from samples of dark-grey schists from Dolna Sasa, Republic of Macedonia. Observa­tions and microphotographs were made on JENA VAL transmitted light microscope. All samples are stored at the Department of Palae­ontology and Stratigraphy, Geological Institute at the Bulgarian Academy of Sciences, Sofia.

Stratigraphical and geographical range

Up to now fourteen species of tubular struc­tures and filaments have been reported from the Silurian and Lower Devonian of Europe, North America and North Africa. Most of them also occur in the Pridoli to Lower Devo­nian marine deposits of the Moesian Platform. In addition, two new species are erected in this study, Porcatitubulus reticulatus sp. nov. from the subsurface of the Moesian Platform, and Ornatifilum macedonensis sp. nov. from the easternmost part of the Republic of Mace­donia.

A summary of previous findings of species of the anteturma Trichomiformis Burgess and Ed­wards is presented in Figs. 4a, b, c. The Silurian and Lower Devonian of the Anglo-Welsh Basin (Burgess, Edwards, 1991) and of Scotland (Wellman, 1995) has yielded the most diversed associations of tubular structures and fila­ments. The greatest part of the localities of dis­persed tubes and filaments occur within the Old Red Sandstone Continent or Laurussia (British Islands, Norway, Poland, USA and Canada). The only records from North Gond­wana are those of Laevitubulus tenuis from Lib­ya (Al-Ameri, 1984) andPorcatitubulus annula­tus from Brittany, France (Moreau-Benoit, 1976). The assemblages of tubular structures and filaments of the Pridoli to Emsian-Eifelian from the southern part of Moesian Platform, North Bulgaria, exhibit similarities to those pre­viously described from coeval sedimentary suc­cessions and confirm Wellman's (1995) conclu­sion that these microphytofossils are geograph­ically widespread.

All previously recorded species of tubular structures and filaments, including the well documented assemblages from the Anglo­Welsh Basin and Scotland, are of Silurian to Lochkovian age. In R -119 Kardam Well from the subsurface of the Moesian Platform, sever­al species of tubes and filaments occurring in

34

TUBE/FILAMENT ~anscof~rcportc~

L. crassus : : : L. frondifcra I I I I ...._, I I

L.lanu I I I

L. plicatus I I

L. tcnuis I I

P. onnulatus I I I

P. spiralis I I

P. microannultus I I I

P. microspira/is I I

P. reticulotus I I I I I I I I

P. strvpus I : C. cri.stotus I I I

0 . ganulatum I I I I I I I I

0 . lorrrt!nsis I I I I r--"1 I I

0 . moccdoncnsis I I I I I I I I

0 . wcnlockium I I I I I I I I

> r ~ r "I: r "!:! w ('r1

!;. ~ c :I. x C! ~

~ Q. Q. oc ..

~ 0 g, ~ §' gl" §. 0 :e 0 < ,.,.. < n ~ -<

-SERIES I STAGE

Fig. 4a. Distribution of dispersed tubes and filaments in the late Ordovician - Middle Devonian of Laurentia. Data from: McGregor, Narbonne (1978); Prat et aL ( 1978); Stro­ther and Traverse (1979); Johnson (1985); Gensel et a/. (1991); Wellman (1993, 1995); Wellman, Richardson (1993)

TIJBEIFILAMENT Range of strata reported

L. crti.U1I.J I _1

L. frondtfua I I t......l I I I I

L. laxiU I I I

L. pllcallu I I

L. tenuil I 1......1 I I I I I

P. QNUI/atu.r I I I

P. qJiralir I I I

P.~ : I : P. mic7wptralts I I I

P.~ I I I I I I I I

P. #TIIpiU I I I c. crtstahu I I I

O. g1Z111114tum I I I

0. lonwn.sts I I ~ I I I I

0. llfiJCetlorrDuts I I I I I I I I

0.~ I ....... I I I I I

i J ~ t I i { r ttl I;;

~ j· t

SERIES I STAGE

Fig. 4b. Distribution of dispersed tubes and filaments in the Late Ordovician - Middle Devonian of Avalonia-Baltica. Data from: Eisenack (1971, 1972, 1977, 1978); Edwards et al. (1983); Smelror (1987); Burgess, Edwards (1991); Haqstrom 1997)

TUBE/FILAMENT Kqe Ol ltrala reported

£. CTCDSU.J : : : L.frondifera I I I I I I I I

L.la:au I I I ~

L. plicatu.r I I I I I I I r-L.tertuls I I '- I I I

P. tl1111ulatw I I I

P. spiralis I I I I I I ~ P. microannultw : : : H : ~ P. microsplralis I I I I I I ....... P. reticulatw I I I 1"""""'1

P. stnrpu.s I I I H c. crlstatus 1 1 1 l,j

O.ganuialrlm I I I ~

0./omensis I I I I I I I I

0. macedoMrtSis I I I H I 1...-1 0. we~lockium I I I I I I I I

i. I:"'

~ t ~ t. f tu tu

f I! g; It

= ~ = ;r f Ill

SERIES I STAGE

Fig. 4c. Distribution of dispersed tubes and filaments in the Late Ordovician - Middle Devonian of Gondwana and peri-Gondwanan Europe. Data from: this work, Moreau-Benoit (1976), AI-Ameri (1984)

the Pridoli and Lochkovian range up into the Emsian. These are: Laevitubulus crassus, L. laxus, L. tenuis, Porcatitubulus annulatus, P. spiralis, P. microspiralis, P. microannulatus, P. reticulatus, P. strupus, Constrictitubulus crista­Ius, Ornatifilum granulatum and 0. macedon­ensis. Single specimens of P. annulatus occur even at the base of the Eifelian stage (Fig. 2). Within the Eifelian of the R-120 Ograzhden well, P. annulatus, L. crassus, L. plicatus and L. tenuis occur (Fig. 4c, see pl. I, fig. 8).

The Pridoli and Emsian of the R -119 Kar­dam well yielded tubes with reticulate wall across the scalariform-bordered pits (Pl. II, figs 7, 9) resembling the dispersed tracheids of Psilophyton charientos documented by Gensel et al. (1991, figs 13C, 14D,E)

As for the palaeogeographical position of the recent Moesian Platform within the Avalonia­Baltica- North Gondwana interface during Sil­urian and early Devonian times, some recently obtained palaeobiogeographical results on chit­inozoans from the Moesian Platform suggest a close relation to contemporaneous North Gondwanan faunas (Lakova, 1995b ). Conse­quently, even the tubular structures and fila­ments from the southern part of Moesian Plat-

form seem cosmopolitan themselves, the palae­obiogeographical affinities of co-occurring Sil­urian and Lower Devonian chitinozoans docu­mented from the area suggest that the Lower Palaeozoic basement of the Moesian Platform is most probably of North Gondwanan origin. This is consistent with the conclusion on a Peri­Gondwanan origin of Paleozoic terrans from the Balkan Peninsula (including the Moesian Platform pre-variscan basement) which has been drawn by Yanev (1997) on palaeontologi­cal, lithological and palaeomagnetical data.

Systematic palaeontology

Anteturma TRICHOMIFORMIS Burgess & Edwards, 1991 Turma TUBIFORMIS Burgess & Edwards, 1991 Infraturma LAEVIMURALI Burgess & Ed­wards, 1991

Genus Laevitubulus Burgess & Edwards, 1991 Type species. Laevitubulus tenuis Burgess & Edwards, 1991.

Laevitubulus crassus Burgess & Edwards, 1991 Pl. I, figs 5-6 1977. Abb.l7. Schraubig gekrummtes Rohrchen, Eisenack,

p. 33, fig. 17. 1982. 'melanosclerits', Edwards, figs. 76-77. 1991. Laevitubulus crassus sp. nov., Burgess, Edwards, p.

48, figs 5-7. 1993. Laevitubulus crass us Burgess & Edwards, 1991, Well­

man, Richardson, pl. 5, fig. 3. 1995. Laevitubulus crassus Burgess & Edwards, 1991, Well-

man, p. 258, pl. 1, figs 6, 11.

Occurrence. R-1 Dalgodeltsi, Pridoli and Lochkovian, R -119 Kardam, Pridoli, · Lochk­ovian and Emsian, R-120 Ograzhden, Eifelian.

Dimensions. Diameter: 12-24 J.Lm; length: 420-500 J.Lm.

Description. Unbranched opaque straight and usually helically curved tubular structure.

Stratigraphical and geographicl range. From the late Wenlock to early Lochkovian in the Ang­lo-Welsh Basin (Burgess, Edwards, 1991 ), early Wenlock - Lochkovian of Scotland (Wellman, 1995), late Wenlock of Ireland (Edwards et a!., 1983), Wenlock of England (Eisenack, 1977).

Laevitubulus laxus Burgess & Edwards, 1991 Pl. I, figs 1, 3 1972. Gewirr von fadenartig dunnen Rohrchen, Eisenack,

pl. 20, fig. 5. 1982. 'narrow smooth tubes', Edwards, figs 17-21. 1983. 'small branched tubes', Edwards et a/., figs 36-39. 1991. Laevitubulus laxus sp. nov., Burgess, Edwards, p. 51,

figs 17-21.

35

1993. Laevitubulus laxus Burgess & Edwards, 1991, Well­man, Richardson, pl. 5, fig. 1.

1995. Laevitubulus laxus Burgess & Edwards, 1991, Well-man, pl. 1, fig. 13.

Occurrence. R-1 Dalgodeltsi, Pridoli and Lochkovian; R-119 Kardam, Pridoli and Em­sian; Osogovo Mts, E. Macedonia, ? Wenlock to Lower Devonian.

Dimensions. Diameter: 6 Jlm; length: 130 Jlm. Description. Light-brown, semi-transparent

tubular structure occurring usually in loosely aggregated wefts.

Stratigraphical and geographical range. Pri­doli of Poland (Eisenack, 1972), basal Wenlock to early Lochkovian of Anglo-Welsh Basin (Burgess, Edwards, 1991), late Wenlock of Ire­land (Edwards et al., 1983), early Wenlock -Lochkovian of Scotland (Wellman, 1995).

Laevitubulus plicatus Burgess & Edwards, 1991 Pl. I, figs 8-1 0 1978. tube-like structure, McGregor, Narbonne, p. 1299,

pl. 2, fig. 7. 1985. smooth-walled tube, Johnson, pl. 13, fig. 2. 1991 . Laevitubulus plicatus sp. nov., Burgess, Edwards, p.

49, figs 8-1 0. 1995. Laevitubulus plicatus Burgess & Edwards, 1991 ,

Wellman, pl. 1, figs 2-3. 1996.Laevitubulus plicatus Burgess & Edwards, 1991, Ed-

wards, Wellman, p. 384, pl.l, fig. 7.

Occurrence. R-1 Dalgodeltsi, Pridoli and Lochkovian; R-119 Kardam, Pridoli, R-120 Ograzhden, Eifelian.

Dimensions. Diameter: 8-l 0 Jlm; length: 80-96 Jlm.

Description. Thin-walled flattened transpar­ent unbranched tubular structure with smooth surface.

Stratigraphical and geographical range. Up­permost Ordovician (Ashgill) to Lowermost Devonian (Lochkovian) of the Anglo-Welsh Basin (Burgess, Edwards, 1991 ), early Lland­overy of Pennsylvania, USA (Johnson, 1985), late Ludlow of Arctic Canada (McGregor, Nar­bonne, 1978), early Wenlock to Lochkovian of Scotland (Wellman, 1995), Wenlock of Wales (Edwards, Wellman, 1996).

Laevitubulus tenuis Burgess & Edwards, 1991 Pl. I, fig. 7 1978. 'unbranched tubular elements', Pratt et a/., p. 131,

pl. 2, figs 5-8. 1982. 'black tube', Edwards, p. 242, fig. 78. 1983. ' larger smooth tubes', Edwards et al., p. 30. 1984. ' tube type 4', AI-Ameri, p. 384, pl. 2, fig. 7. 1991 . Laevitubulus tenuis sp. nov., Burgess, Edwards, p. 47,

figs 1-4. 1993. Laevitubulus tenuis Burgess & Edwards, 1991 , Well­

man, Richardson, pl. 4, fig. 8. 1995. Laevitubulus tenuis Burgess & Edwards, 1991, Well­

man, p. 258, pl. 1, fig. l.

36

Occurrence. R -1 Dalgodeltsi, Pridoli and Lochkovian; R-119 Kardam, Pridoli, Lochk­ovian and Emsian, R -120 Ograzhden, Eifelian.

Dimensions. Diameter: 22-26 Jlm; length: min 180 Jlm.

Description. Straight, unbranched black opaque flattened tubular structure.

Stratigraphical and geographical range. Late Wenlock of South Wales and Ireland (Burgess, Edwards, 1991), early Wenlock- Lochkovian of Scotland (Wellman, 1995), Llandovery of Vir­ginia, USA (Pratt et a/., 1978), Silurian to early Devonian of Libya (Al-Ameri, 1984).

Infraturma ENDOMURALI Burgess & Ed­wards, 1991

Genus Porcatitubulus Burgess & Edwards, 1991 Type species. Porcatitubulus annulatus Burgess & Edwards, 1991.

Porcatitubulus annulatus Burgess & Edwards, 1991 Pl. II, figs l, 2, 5, 8, 11 1971. Geringeltes Rohrchen mit Bewuchs, Eisenack, fig, 30. 1972. Gewirr von fadenartig dunnen Rohrcben, Eisenack,

pl. 20, fig. 4. 1976. Tracheide annelee, Moreau-Benoit, p. 42, pl. 9, fig. 7. 1979. tubular structures, Strother and Traverse, pl.3, fig. 15. 1982. tube showing annular thickening, Edwards, p. 241,

figs 75, 68. 1983. fragments of ornamented tubes, Edwards et a/., p.

26, figs 32, 33. 1991. Porcatitubulus annulatus sp. nov., Burgess, Ed­

wards, p. 55, figs 22-30. 1991. Anastomosing annular nematoclast, Gensel et at.,

fig. sc. 1993. Porcatitubulus annulatus Burgess & Edwards, 1991 ,

Wellman, Richardson, pl. 4, fig. 5. 1995. Porcatitubulus anuulatus Burgess & Edwards, 1991 ,

Wellman, p. 265, pl. I, figs 5, 12. 1996. Porcatitubulus annulatus Burgess & Edwards, 1991 ,

Edwards, Wellman, p. 384, pl. 1, figs. 8, 14. 1996. Porcatitubulus ? sp. Burgess & Edwards, 1991 , Par-

is, Grahn, pl. 2, figs 7-8. 1997. Porcatitubulus sp., Haqstrom, p. 310, fig. 8P.

Occurrence. R -1 Dalgodeltsi, Pridoli and Lochkovian; R-119 Kardam, Pridoli, Lower Devonian and Eifelian, R-120 Ograzhden, Eife­lian.

Dimensions. Diameter: 16-24 11m; length: min 190 Jlm.

Description. Straight, transparent unbranch­ed flattened tube with internal annular thicken­ing of the wall.

Stratigraphical and geographical range. Late Ludlow of South Wales (Edwards, 1982), Wen­lock of Wales (Edwards, Wellman, 1996), late Wenlock oflreland (Edwards et a/., 1983), bas­al Wenlock to Lochkovian of the Anglo-Welsh Basin (Burgess, Edwards, 1991), early Wenlock

to Lochkovian of Scotland (Wellman, 1995), Pridoli of Poland (Eisenack, 1972), Pridoli of 'Beyrichia-Kalk', erratic deposits of Baltica Re­gion (Eisenack, 1971 ), Pridoli and Lochkovian of Podolia, Ukraine (Paris, Grahn, 1996), Wen­lock of USA (Strother, Traverse, 1979; Gensel et a!., 1991 ), Lochkovian of the Armorican Massif, Brittany, France (Moreau-Benoit, 1976), Wenlock and Ludlow of Gotland, Swe­den (Haqstrom, 1997).

Porcatitubulus microannulatus Wellman, 1995 Pl. III, figs 4-5 1993. 'tube with annular internal microthickenings', Well­

man, Richardson, pl. 4, fig. 9. 1995. Porcatitubulus microannulatus sp. nov., Wellman,

p. 266, pl. 3, figs 1-3, 5. 1996, Porcatitubulus? sp. Burgess & Edwards, 1991 , Par­

is, Grahn, pl. 2, fig. 9.

Occurrence. R -1 Dalgodeltsi, Pridoli, and R-119 Kardam, Pridoli and Emsian.

Dimensions. Diameter: 38-46 J..Lm; length: 40-64 J..Lm.

Description. Straight, unbranched transpar­ent flattened tubes with numerous annular in­ternal microthickenings.

Stratigraphical and geographical range. Ear­ly Wenlock to Lochkovian of Scotland and Early Wenlock to Lochkovian of Southern Brit­ain (WeHman, 1995), Pridoli of Podolia, Ukraine (Paris, Grahn, 1996).

Porcatitubulus microspiralis WeHman, 1995 Pl. II, figs 4, 10

1978. 'unbranched tube with fibrilar constriction' , Prat et al., pl. 2, fig. 9.

1979. 'tubular structures', Strother, Traverse, pl. 3, fig. 14. 1991. Porcatitubulus spiralis Burgess & Edwards, sp. nov.,

p. 57, figs 48-50, 52-54. 1993. 'tube with spiral internal microthickenings' , Well­

man, Richardson, p. 178, pl. 4, fig. I 0. 1995. Porcatitubulus microspiralis sp. nov., Wellman, p.

266, pl. 3, figs 4, 7-8.

Occurrence. R-119 Kardam, Emsian. Dimensions. Diameter: 25-29 J..Lm; length: 90-

100 J..Lm. Description. Straight, transparent flattened

tubes with numerous parallel internal spiral microthickenings.

Stratigraphical and geographical range. Ear­ly Wenlock to Lochkovian of Scotland (WeH­man, 1995), Early Wenlock to Lockovian of Southern Britain (Wellman, 1995), Llandovery­Wenlock of Pennsylvania, USA (Strother, Traverse, 1979).

Porcatitubulus reticulatus sp. nov. Pl. III, figs 1-3, 7-9

Type. Holotype: Pl. 3, fig. I, sample 2101, slide 2101; paratypes: pl. 3, figs 2-3, 7-9.

Locality of holotype. R-1 Dalgodeltsi Well, Kalarashi Formarion, depth 4879-4885 m.

Horizon of holotype. Lochkovian, Fungo­chitina lata chitinozoan Zone.

Derivation of name. Reticulatus - reticulate, refers to wall structure pattern.

Occurrence. R-119 Kardam, Pridoli and Em­sian, R -1 Dalgodeltsi, Pridoli and Lochkovian.

Dimensions. Diameter: 26-50 J..Lm; length: 44-170 J..Lm; annular thickenings - 1-2 J..Lm wide, at distance of 4-8 J..Lm.

Diagnosis. Straight, semi-transparent dark­brown tubular structure, with solid, rarely spaced (4-8 J..Lm apart) annular internal thicken­ings and reticulate wall surface.

Description. Parallel sided, straight or slight­ly curved tubular structure, partly flattened. It is 26-50 J..Lm in diameter and 44-170 J..Lm long. The wall is reticulate, irregularly polygonal, dark-brown, semi-transparent. The internal thickenings are prominent, black, 1-2 J..Lm wide and relatively rarely spaced at distance of 4-8 J..Lm. No branching and terminations observed.

Comparisons. P. reticulatus sp. nov. differs from P. annulatus in having less numerous, rig­id, more rarely positioned annular internal thickenings and reticulate structure of the wall surface. P. reticulatus resembles very much in its microporate wall and annular thickenings the G-type conducting elements (Kenrick et al., 1991) of Gosslingia breconensis Heard, an Early Devonian (Siegenian) zosterophyll land plant. The earliest radiation of zosterophyll vascular plants was documented from the end of Loch­kovian at Brecon Beacons in Wales (Wellman et a!., 1998).

Stratigraphical and geographical range. Pri­doli, Lochkovian and Emsian of the Moesian Platform, Bulgaria.

Porcatitubulus spiralis Burgess & Edwards, 1991 Pl. II, figs 3, 6, 12, 13, pl. IV, figs 5, 6

1972 Spiraltracheide, Eisenack, pl. 20, fig. 22. I 977 Spiralgefass, Eisenack, p. 32, fig. 27. I 978 spirally thickened tube, McGregor and Narbonne,

pl. 2, fig. 6. 1978 banded tubes, Pratt et a!., pl. I, figs 5-6, pl. 2, fig. 9. 1979 tubular structures, Strother and Traverse, pl. 3, fig. 12. 1982 isolated ornamented tube, Edwards, p. 241, fig. 74.

37

1987 tracheid-like tube, Smelror, p. 147, fig. 41. 1991 Porcatitubulus spiralis sp. nov., Burgess, Edwards, p.

57, figs 31-54. 1991 Primary spiralled nematoclasts, Gensel et a/., fig.

5A, B. 1993 Porcatitubulus spiralis Burgess & Edwards, 1991 ,

Wellman, Richardson, pl. 4, fig. 4. 1995 Porcatitubulus spiralis Burgess & Edwards, 1991,

Wellman, p. 265, pl. 1 figs 4, 10. 1996 Porcatitubulus spiralis Burgess & Edwards, 1991,

Edwards, Wellman, p. 384, pl. 1, figs 9-12.

Occurrence. R -1 Dalgodeltsi, Pridoli and Lochkovian; R-119 Kardam, Pridoli, Lochk­ovian and Emsian.

Dimensions. Diameter: 12-28 J.J.m; length: 36-120 Jlm.

Description. Straight, transparent, rarely branching tubular structure showing internal spiral thickening of the wall.

Stratigraphical and geographical range. Bas­al Wenlock to early Lochkovian of the Anglo­Welsh Basin (Burgess, Edwards, 1991), Wen­lock of Dudley, England (Eisenack, 1977), Wenlock of Wales (Edwards, Wellman, 1996), early Wenlock to Lochkovian of Scotland (Wellman, 1995), Llandovery'? and Wenlock of Norway (Smelror, 1978), Pridoli of Poland (Eisenack, 1972), Silurian of USA and Canada (Pratt et al., 1978; McGregor, Narbonne, 1978; Strother, Traverse, 1979; Gensel et al., 1991 ).

Porcatitubulus strupus Wellman, 1995 Pl. III, fig. 6 1979. 'tubular structures' , Strother, Traverse, pl.3, fig. 13 1991. 'internal fibrilar nematoclast', Gensel et al., fig. 50. 1993. 'tube with wide 'strap-like' internal thickenings, Well-

man, Richardson, pl. 5, fig. 2. 1995. Porcatitubulus strupus sp. nov., Wellman, p. 267, pl.

4, figs l -2, 4, 6-9.

Occurrence. R -1 Dalgodeltsi, Pridoli and Lochkovian, and R -119 Kardam, Pridoli and Emsian.

Dimensions. Diameter: 28-36 J.J.m; length: 110 Jlm.

Description. Straight, transparent flattened tubes with internal strap-like thickenings.-

Stratigraphical and geographical range. Ear­ly Wenlock to Lochkovian of Scotland (Well­man, 1995), Early Wenlock to Lochkovian of Southern Britain (Wellman, 1995), Llandovery and Wenlock of Pennsylvania, USA (Strother, Traverse, 1979), Wenlock of Pennsylvania (Gensel et a!., 1991 ).

Infraturma EXTRAMURAL! Burgess & Ed­wards, 1991

Genus Constrictitubulus Burgess & Edwards, 1991

38

Type species. Constrictitubulus cristatus Bur­gess & Edwards, 1991.

Constrictitubulus cristatus Burgess & Ed­wards, 1991 Pl. I, figs 2, 4 1991. Constrictitubulus cristatus sp. nov.; Burgess, Ed­

wards, p. 59, figs 12-16. 1995. Constrictitubulus cristatus Burgess & Edwards, 1991,

Wellman, pl. l, figs. 7-9. 1996. Constrictitubulus cristatus Burgess & Wellman, 1991,

Edwards, Wellman, p. 384, pl. l , fig. 13. 1997. Constrictitubulus cristatus Burgess & Edwards, 1991,

Haqstrom, p . 310, fig. SQ.

Occurrence. R-1 Dalgodeltsi, Pridoli and Lochkovian; R -119 Kardam, Pridoli, Lochk­ovian and Emsian.

Dimensions. Diameter: 6 J.!m; length: 84-126 Jlm. .

Description. Tubular structures wtth external annular thikenings, black, opaque, straight or slightly sinous.

Stratigraphical and geographical range. Late Wenlock to early Lochkovian of the Anglo­Welsh Basin (Burgess, Edwards, 1991), early Wenlock to Lochkovian of Scotland (Wellman, 1995), Wenlock and Ludlow of Gotland, Swe­den (Haqstrom, 1997).

Turma FILIFORMIS Burgess & Edwards, 1991 Infraturma ORNATIMURALI Burgess & Ed­wards, 1991

Genus Ornatifilum Burgess & Edwards, 1991 Type species. Ornatifilum granulatum Burgess & Edwards, 1991 .

Ornatifilum granulatum Burgess & Edwards, 1991 Pl. IV, figs 1-4, 7 1991. Ornatifilum granulatum sp. nov., Burgess, Edwards,

p. 60, figs 55-60. 1996. Ornatifilum granulatum Burgess & Edwards, 1991,

Edwards, Wellman, p. 384, pl. I, fig. 15.

Occurrence. R-1 Dalgodeltsi, Pridoli and Lochkovian; R -119 Kardam, Pridoli, Lochk­ovian and Emsian.

Dimensions. Diameter: 4-6 J.J.m; length: 43-130 Jlm.

Description. Flattened, transparent, bran­ched septate filaments, mid-brown in colour. Septae occurring rarely at branchings but com­monly between them at points of constrictions; external wall covered by very fine grana.

Stratigraphical and geographical range. Bas­al Wenlock to Early Lochkovian of the Anglo­Welsh basin (Burgess, Edwards, 1991 ), Wen­lock of Wales (Edwards, Wellman, 1996).

Ornatifilum macedonensis sp. nov. Pl. IV, figs 8-11

TYJX!. Holotype: pl. 4, fig. 9, slide M 18; para types: pl. 4, figs. 8, 10-11.

Locality of holotype. Dolna Sasa, eastern­most part of the Republic of Macedonia, Rash­cha Formation.

Horizon of holotype. Exact age of the type horizon unknown. The stratigraphic range of Rashcha Formation is Silurian to Lower Devo­nian.

Derivation of name. After the type area, Macedonia.

Occurrence. Dolna Sasa, E Macedonia, Rashcha Formation; R-1 Dalgodeltsi Well, Pri­doli; R-119 Kardam Well, Pridoli and Emsian.

Dimensions. Diameter: 4-5 Jlm; length: 94-160 Jlm; distance between septae: 30-50 Jlm.

Diagnosis. Straight or branched flattened transparent filaments, 4-5 Jlm in diameter and at least 90-1 00 Jlm long, covered by micrograna less than I mm high; septae without constric­tions placed at distance of 30-50 Jlm.

Description. Elongate, straight or occasional­ly branching, transparent light-brown fila­ments, 4-5 Jlm in diameter, at least 100 Jlm long. The surface is externally covered by mi­croscopic grana of size less than 1 Jlm. Septae are parallel to each other and placed at dis­tance of 30-50 Jlm, without constrictions and not associated with branchings. The filaments often occur together in loose aggregates rather than as single specimens.

Comparison. The new species differs from 0. granulatum in lacking constrictions at places of septae and by hardly visible ornamentation on the wall surface. There are no flask-shaped pro­tuberances characteristic of 0. lornensis Well­man. Dudleyia wenlockia Eisenack, 1978 from the Lower Wenlock of Dudley, England, is a problematic microfossil representing thin, transparent septate filaments with fine grana on the wall. This species fits to the generic diagno­sis of Ornatifilum, being at the same time differ­ent from both 0. granulatum and 0. lornensis and very similar to 0. macedonensis sp. nov. The latter differs from Eisenack's species in that the diameter is twice smaller and the sep­tae are much closely positioned.

Stratigraphical and geographical range. Wenlock to Lower Devonian, Eastern Mace­donia, Pridoli and Lower Devonian in the sub­surface of the Moesian Platform.

Palaeobotanical and palaeoenvironmental applications

The emergence of plants on land is one of the most important events in the entire history of life on earth. Recent palynological and palae­obotanical data concerning the origin and de­velopment of pre-Devonian land plants indi­cate two main phases in the development of terrestrial floras: 1. Llanvirn to Aeronian. There are no land plant megafossils, trilete spores or tubular structures with internal thickenings until the late Aeronian. Palynofacies contain mainly cryptospores and in some Caradoc and Ashgill localities also cuticles. The only tubular struc­ture reported is Laevitubulus plicatus from the Ashgill of the British Isles (Burgess, Edwards, 1991 ). Taking into account the resemblance of cryptospores from nonmarine deposits to tet­rads of modern bryophytes, it is suggested that this stage of the land plant evolution represent­ed a bryophyte-like grade of organization (Gray, 1985; Richardson, 1996). 2. Late Aeronian to Early Devonian. Silurian land plant macrofossils are first reported from the Late Wenlock and occur rarely in near­shore marine Ludlow and Pridolian sediments. In contrast, there is an abundant and geograph­ically widespread record of spores (trilete spores and cryptospores) and tubular struc­tures with internal annular and helical thicken­ings since the late Llandovery (Fig. 5).

The palaeobotanical affinities and relation­ships of pre-Devonian tubular and filamentous macerals to the early evolution of vascular and non-vascular plants have been discussed by Gray, Boucot (1977), Pratt et a/. (1978), Gray (1985), Burgess, Edwards (1991), Wellman (1995) and Edwards, Wellman (1996). Internal­ly thickened annular and helical tubes inter­preted as water-conducting and supporting structures, together with smooth, externally or­namented tubes and septate filaments occur to­gether with completely preserved macrofossils of Nematophytales (land plants of uncertain origin) and are most likely related to them. Many of the Aeronian to Lower Devonian tu­bular assemblages are from nonmarine depos­its which suggests probable fresh-water or ter­restrial origin. It is not excluded that some tu­bular structures belong to algae or any other land plants of unknown affinities. The present

39

author's observations on Pridoli and Lower Devo­nian chitinozoans from the Moesian Platform did not confirm the suggestion that smooth tubes (Laevitubulus plicatus) are fragments of chitino­zoans. The septate filaments (genus Ornatifilum) are considered by Sherwood-Pike and Gray (1985), Wellman (1995) as related to fungi.

Certain complex tubular structures with re­ticulate wall pattern across the aperture of the scalariform bordered pits from the Pridoli and Emsian in the Moesian Platform resemble very much isolated trimerophyte remains such as the tracheids of Psilophyton charientos illustrat­ed by Gensel et al. (1991, figs 13C, 14D,E). Such tracheid types are known from the Lower Devonian (Siegenian) of the Northern Hemi­sphere (Canada). Further, Porcatitubulus retic­ulatus sp. nov., morphologically resembling the G-type conducting elements of the zostero­phyll Gosslingia breconensis from the Siegenian of Wales, is found in Bulgaria in older strata of Pridoli and Lochkovian age. This record of dis­persed tubular elements of probably trimero­phyte and zosterophyll affinities in the upper­most Silurian (Pridoli) of the northern periph­ery of North Gondwana (Figs 4c, 5) confirms Gensel et a!. 's (1991) suggestion that more complex terrestrial plants emerged in the Sou­thern Hemisphere earlier than in the Northern Hemisphere.

The tubular structures described in this work occur in organic-rich black shales deposited on the shelf on the northern margin of Gondwana under conditions of temperate climate, anoxia and high organic productivity. These strata be­long to a prominent Silurian-Lower Devonian

lithofacies belt compnsmg Northern Africa, parts of Southern Europe and the Middle East. Throughout the studied Pridoli and Lower D e­vonian black shale sequences of the R-1 Dal­godel tsi and R -119 Kardam wells, the ass em­blages of tubular structures and filaments are associated with abundant microplankton (acri­tarchs), commonly occurring chitinozoans and sporadic scolecodonts, as · well as macrofossils (brachiopods, bivalves) in some core intervals. This fossil content suggests an open marine shelf depositional environment. The occur­rence of tubular structures and filaments in all samples together with the abundant miospores and some cuticle fragments indicates a con­stant input of land plant microfossils possibly due to the close proximity at land.

Palaeogeographical and biostratigraphical applications

Most of the species of tubular structures and filaments have previously been reported from localities of Late Ordovician to Lochkovian age from Baltica-Avalonia and Laurentia. The di­verse associations of 13 species from Bulgaria documented in this study suggest that the taxa of anteturma Trichomiformis were distributed over a wider palaeogeographical area which in­eluded also the northern periphery of North Gondwana. Thus, the early land plants related to tubular structures and filaments occupied at least two palaeogeographic provinces during the Silurian and Early Devonian - Laurentia­Baltica and North Gondwana.

Chronostratigraph.., Thbular assemblag_e Species of tubular and filamentous structures

40

Eifelian Laevitubulus

' "' "' ' t;i

:I "'

= I I I I Bl I I ~ I 11·11 "' Em sian ' ·a "' ... 0 ' : ~ ' .,. . -3: U • ..... ..c '

Pragian ' ;!:l! ~ · ' "' .. : <> : > ' ' ·;;; "'' u P. reticulatus ' : :.o ., . .~ : l3 i _: ~ : § 5 E : !:! • c: : Cl 5 ~!" !3 . .

il :; : 0 •

Q,. g >, ! "' ~ "'

.. "' ·c - 3d E .D

Lochkovian .:: :.::l :I E .s ..c:: "' :I Q,. u !! u ..9 .., '3 "' "'

~ .~ c. : :::l "' ~ § 5 u '13 ., :I 0

~ ~

~ I ] !l .,

] Q,. ·s :I ; i3 ~ t; u Pridoli "' "'

i '"3 to ~

... ~ .. "' = ~ ~ ~

= ... :; !:1 ;:1 ;:1 .&J

u ;:1 ... '"3 '"3 '"3 '"3 -~ ~ § ;.:l '"3 '"3 '"3 ·~ "'

0 Q,. -a .&J .&J .&J E "' c Ludlow .&J .&J .&J j ;:1 .E B ti

~ '"0

"' ~ 2 2 B ·~ ·5 ·;:~ '5 ~ 0 ·o; ·c P. spiralis '"3 ·~ ·~ ·~ "' ~ "' u .,

"' ~I ..c: = u u u ... c e u

~ Wenlock s :3 :3 :3 ... ... ... i. 8 "' i. ~ ~ ~ 0 !!:: "> Llandovery ····-

., j

-d L. plicatus _Q_ Ashgill

Fig. S. Generalised stratigraphic range chart of the known tubular and filamentous species and definition of tubular assemblages

The independent stratigraphic control on chitinozoans and conodonts has proved that in the R -119 Kardam and R -120 Ograzhden wells all thirteen tubular structures and filaments oc­curring in the Pridoli and Lochkovian range up into the Emsian - Eifelian (Fig. 5). This stresses the need for further study of such phytodebris in post Lochkovian strata.

Previously, two stratigraphically distinct tu­bular assemblages were identified: an older, Ashgill to Llandovery, assemblage of smooth tubes, and a more diverse, Wenlock to Early Devonian, assemblage of internally and exter­nally ornamented tubes and septate filaments (Burgess, Edwards, 1991; Edwards, Wellman, 1996). This study suggests that since the latest Silurian (Pridoli), new elements appear in the tubular assemblages at least in North Gondwa­na. These are tracheid-like structures related to zosterophylls (P. reticulatus) and trimerophytes (tracheids of Psilophyton). A less diverse assem­blage of mainly smooth tubes of Laevitubulus is documented from the Eifelian (Fig. 5).

The existing data on the stratigraphic occur­rence of dispersed tubes and filaments allow identification of four successive tubular assem­blages: 1. L. plicatus assemblage. Smooth tubes, low diversity, Ashgill to Aeronian. 2. P. spiralis assemblage. Incoming of diverse internally and externally ornamented tubes and septate filaments, Aeronian to Ludlow. 3. P. reticulatus assemblage. Incoming of tra­cheids of vascular plants (P. reticulatus, G-type elements), high diversity, Pridoli to Emsian. 4 Laevitubulus assemblage. Low-diversity, mainly smooth tubes, Eifelian.

Acknowledgements. This work was undertaken at the De­partment of Palaeontology and Stratigraphy, Geological Institute, Sofia. It is funded by the Bulgarian National Research Fund (Project NZ-813/1998). I express my grat­itude to Prof. Dianne Edwards, University of Wales, Col­lege of Cardiff, and Dr Charles Wellman, University of Sheffield, for critical remarks on the manuscript. This paper is a contribution to IGCP Project 421 "North Gondwana Mid-Paleozoic Biodynamics".

References

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Boncheva, I. 1995. Conodont biostratigraphy of the Mid­dle Devonian in North Bulgaria. - Rev. Bulg. Geol. Soc., 56, 3, 35-46 (in Bulgarian with English summary).

Burgess, N.D., Edwards, D. 1991. Classification of upper­most Ordovician to Lower Devonian tubular and fila­mentous macerals from the Anglo-Welsh Basin. - Bo­tanical Journal of the Linnean Society, 106, 41-66.

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