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: [email protected] 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
a:BTbl 6&1J!H HaH.neHbl B oca.nKaX 3MCKOfO H 3HQJeJJbCKOB03pacTa, 'ITO npo.non~aeT HX crpaTHrpaQJHtJecKoe
;acnpocTpaHeHHe nocne JJOXKOBCKoro aeKa. Haxo.nKH XHbiX -rpy6qaT&IX CTPYKTYP. HanoMHHaJOmHe Tpaxe
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
I Deptl(m) I ~ --\0
~ CBITINOZOANI ~
ZONE
L CI'GUIU
L. laxu.r
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.P.~~
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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#" -. . ~ ,
t ~
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PLATE III
1 2
/ 7
9
PLATE IV
6
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9
R 1 D l d Its' - ago e 1 TUBES AND FILAMENTS
~ a .~
:u~ ~~ a ~ a ~ ~
~~ 1::
~ 1::
~~ i j a ·::::i ...5! .I 1 ~ I ~ i
~ ] ;:s ;:s ~ ·~ ~ i 1,) 1:1, ~ ~ E 2! ·~
~ ~ ~ ~ ~ ~ ~ ~ ~ u 0 0
z 0
~ .--
~
~ B
~ rill ....... t.-' ~
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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